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Amal Catalog page12

Vincent Carburators

The subject of rich discussion: Click for Blow-up of Standard Amal Carb for Vincent
Tuning 276/289/229 Amal Standard carbies:     5/1/2010

If you do use an 'ultrasonic cleaner' watch the process very closely... ultrasonic cleaners dissolve aluminum... after the crud is gone... you Have to know when to take the componant out or you will have surface degradation.  Many modern firearms have numerous aluminum componants.  We have had problems with this issue in our shop...we no longer use ultrasonic cleaning if all of the componants do not jump to the magnet... Dave R.  3/10/10  read next post
Not if you use the right cleaning solution.    John Mead  3/10/10
Sticking slides seem to occur in about fifty to sixty percent of the
Concentrics coming through the shop. In paired carbs it may be one or both. In general sticking occurs toward the top of the slides travel range but it can also occur at other points in the travel. It invariably occurs in or close to the plane of the carb bore.

 First, having removed float bowl, cables, choke etc it's necessary to thoroughly clean the slide and bore with carb cleaner and if required a worn kitchen scouring pad to remove any clinging grit or debris. Blow everything out with air.  Unless there is other work to do on the head or flange the carb body(s) is left undisturbed attached to the head. Now test the slide by passing it down the slide bore. It should drop freely. If it hangs at any point then grasp the top of the carb slide bore between thumb and forefinger starting at right angles to the carb bore and press firmly. Surprisingly often the slide will now drop freely on it's way. The slide bore can easily be slightly deformed just by such hand pressure. By varying the pressure point around the slide bore to see where it best frees up the slide the plane of the deformation can often be determined quite accurately by this method. Upon release of the thumb and finger pressure the bore will spring back to it's deformed shape so this is only useful for determining where and in what plane the bore is deformed. If this method fails to free slide then there has generally been sufficient deformation to produce noticeable wear on the bore and/or slide. Make a visual inspection down the bore and on the slide. Most times you will see a highlight polished or scuffed area running vertically in the bore or on the slide which will tell you the plane in which it is sticking. It is nearly always along or close to the plane of the carb bore.

Now comes the tricky bit which requires some practice and "feel". Having determined where applied pressure on the bore frees the slide wrap the top of the bore with cloth or cardboard and using a suitably sized pair of  channel locks squeeze the bore at that point to permanently "reshape" it. It does not need a lot of pressure to do this so it should only be done very judiciously. Try the slide again. You will soon tell whether it moves more freely or not. Repeat this process very carefully and at different points as needed until the slide drops freely. Usually this takes about fifteen to twenty minutes to achieve. Once the slide drops freely it will continue to do so without problem. Now I know to some of you high tech purists this may all sound rather uncouth, brutish and haphazard but after just a little practice one can become very exacting and accurate in the technique both from the perspective of where to apply pressure and how much to apply. Only in the rarest of circumstances, and sadly often where the owner has tried to "fix" things and really buggered things up, is it ever necessary to remove metal from either the slide or the bore. Doing so is very undesirable and merely accentuates any wear characteristics in the performance of the carb on reassembly.

Other points regarding concentrics. Eighty percent of the time the float bowl leaks because it has been overtightened on the gasket and, as described by Max, the bowl flange becomes distorted with the screw hole tabs being raised upward. Easily cured with judicious use of a plastic mallet and flat file. Sometimes the float will stick because either the new gasket tends to trap it (trim accordingly) or the ends of plastic pivot holes on the float (particularly new ones) foul the casting of the bowl. File a couple of mms of each side of the float pivot taking care afterward to make sure the holes remain fully open and the float spindle turns freely in them.

 Invariably when customers complain that they can't get the bike to idle properly (all else being correct) it is due to the pilot jet being blocked in one or both carbs. The pilot jets on concentrics for some reason seem to block up very easily with gum, particularly if the bike is not used for any length of time. Cleaning them needs care. Blowing with air or squirting carb cleaner into the pilot air screw hole generally does not unblock them. Cleaning the jet properly can only be done by the careful use of the correct size micro drill bit fed and twisted carefully by hand through the pilot air screw hole and on through the jet orifice. Again this takes practice and care.   timothy holcroft 3/10/10

Sticking Amals : Bolting a flat steel plate onto the carburetor flange prior to honing the carburetor bore isn't recommended.  If one were to do so, when the crushed flange is released from the carburetor flange, the high spot areas which were honed away now become low spots.  If you were to use a flange in the process, you would first have to flatten and true the carburetor flange prior to honing the carburetor slide bore.  It's not necessary, in fact it's a waste of time, to prebolt a flange prior to honing.    I've done this probably 30 or 40 times, so I know from personal 'hand's on' experience what works and what doesn't.

A further explanation as to why the ears of the flange bend and distort with a thick paper gasket:  The surface area of the paper gasket around the carburetor opening has more area than the paper gasket material around the manifold's studs.  When the pressure is applied, pulling the flange surfaces together with the nuts, the paper gasket around the stud area, which is less, crushes more easily, thereby bending the ears during the tightening process, and distorting the carburetor body bore.  Using a very thin gasket and two flat surfaces, distortion is virtually eliminated, even when over torqued.

New or recently rebuilt Amal carburetors that have been cleaned properly, do not stick.  Carburetors that have many hours on them, and are ridden by individuals who don't necessarily hit the throttle stop from stoplight to stoplight, form a resin buildup above the top of the carburetor slide around the carburetor slide bore.  When the carburetors are open to full bore, and find their way into the top of the slide bore where they're not normally run, the resin buildup causes them to stick sometimes.  I've never heard of a new set of Amal carburetors sticking when properly installed, i.e., flat flanges and free running cables.  Problems only arise after many hours of use, or after an inexperienced fettler has been at it.   Max Lambky  3/10/10

Amal carburetors have a tendency to bend the flange ears and sometimes distort the slide bore.  The fix should be to make the slide fit the bore by truing the slide bore with a brake cylinder hone.  Don't sand or polish the carburetor sleeve, as this will cause an improper clearance between carburetor bore and cylinder sleeve.  With a large flat file, dress the flange face flat.  You'll notice that high spots will appear on the outer convex portion of the ears.  This is due not so much to over tightening, but to the use of a too thick gasket.  It's also a good idea to check the manifold flange as well, for flatness.  Correct as necessary.  For best results make your gasket as thin as possible.  I use the glossy cover of motorcycle magazines, and a bit of Permatex.   Max Lambky  3/10/12

The classical method for setting remote floats (e.g. on GP carbs) is to make up a bottom nut with a piece of capillary tubing attached, and see where the fuel level actually is. On a GP it should be 1/8" below the centreline of the pilot jet, and I have always assumed it will be the same for a 289 (which is what I use) and for any other Amal carb.  I did not do this for my twin since it would have meant making two different bottom nuts, but following a hint from Big Sid, realised that my front plug was consistently sooty (not oily) and since the jetting etc was identical front and rear, this was probably because the float level was too high on the front pot. So I rotated it downwards first 1/16" - smoother running - then another 1/16" - as near as damn perfect. It completely transformed the bike, particularly in traffic and at low speeds.  Moral of story: however much faffing about is involved, it is well worth while. A Vincent with two identical pots is a FAR nicer machine than one without, and provides a positively liquid power delivery.   Tom - Sunbeam  3/10/10
I use 930's on my '49 shadow and get good starting and running. I did some of the mods described in your URL but not the one about boring out the low speed jet. I didn't want to get that invasive. I reset the fuel level and I did cut away half the fuel feed nozzle. I figure the fuel level setting  is what concerns the engine and carb for proper operation and measuring that is more accurate than measuring
the float position. If one float weighs a little more than another or has some fuel in it or dirt on it , it may measure in the right place but the fuel level won't necessarily be right. I gently clamped just the
float bowl with float and needle installed level in a vise and fed gas in the inlet via a tube and funnel until the float stopped the gas feed. The fuel level should be close to .2 inches below the rim of the bowl
sans gasket and is easily measured unlike a monoblock . You may need to  hold the float hinge down the way it would be when installed clamped under the gasket by the body. Adjust the fuel level as described by heating the bowl (after you  empty it!) and using a drift to move the brass insert that houses the needle valve and recheck the level. This was wrong on both my new carbs. One was so far off the  tickler pin wouldn't reach the float so I couldn't prime that side. Once the fuel depth was raised the float came up higher and I could prime it properly.  I run the needle in the lowest setting  and it starts easily even at 32 degrees F.  Mike Hebb  3/10/10

 Here is what I have been using in my 30mm Mikuni round slide Carbies:
1. Main Jet  #190
2. Pilot Jet  #45
3.  Needle Jet  159 Q-2
4.  Jet Needle  6DH4
5.  VM34/110 2.5
6.  Air Jet  BS30/97 2.0
7.  Fuel Needle VM34/39 3.3
8.  I use two  No. 002-351 Cable Type Starter Systems connected to the standard Amal choke and splitter.

 I think 32mm Mikuni's are a little large unless you are going for real high speed performance and have the correct camshaft and gearing. Even my 30mm may be a little larger than necessary. Even 28mm are larger than the Shadow carbs and Mikuni's certainly have better flow, size per size, than the old remote float Amals.  All and all, they have been very reliable and run sweet when tuned in.  Ken Smith 12/7/09

Throttle Slide Clearance: The seal is made by "sucking" the slide against the body at the back. What is important is 1) that the slide will slide easily, particularly when closing and 2) that the front and back faces of the slide are not worn, particularly the back (engine) face, because then it won't seal against the body in the mid-range.  Better safe than sorry, but I seem to have about 2 to 4 thou on such slides I have that are new. The upside of larger diametral clearance is safety. The downside is that there is more rattling room and wear is faster. It is fastest on plain brass slides, slower on chromed ones, for obvious reasons.   Sunbeam  11/12/09

389 Monoblocs were used on the "D" with the float bowl on the left and 689 Monoblocs have the float bowl on the right. John Mead  7/27/09
With modern fuel the only way to set your carburation up properly is either use a rolling road or buy a real time air fuel ratio meter.   I have bought a Luminition kit that runs off of a 12volt supply.  All you have to do is poke the sensor up the exhaust pipe and go for a ride, the display is easy to read and is real time via the wide band sensor (remember you only get use full data when the engine is under load).  The results are very intrusting and on all the Vins I have tried so far, I have found them all to be running very rich on the main jet.   My bike is running  8.5/1 compression ratio with a good set of 276 carbs and I am down to a 140 main jet and have done 1500 miles like that, and that included a good thrashing around the TT course last year.  You can buy the kit for around 250 so if a few of you get together and split the cost it would work out cheaper than a couple of hours on the dyno.    Andy  7/8/09

Amal parts:

Milnar Amal GP2 parts:    Bruce Metcalf

I do recommend the fabrication of a float fuel level gauge comprising a bottom nut drilled and tapped to take a needle jet, over which a length of transparent fuel line of the kind used on model aircraft motors can be slipped. When this is held vertically against the carb and the fuel turned on, the level will correspond to that within the float chamber, which is invisible, and can be checked against where it should be in relation to the bottom of the pilot adjuster screw and its threaded hole. An invaluable little tool, no matter what method you use to rectify the fuel level.  Prosper Keating  5/21/09
K&N Air Filter for a Comet:    (K&N - K33RU0160, RU0160)

The Amal spec sheet for 1955-1961 says for D Prince and Shadows that main jet should be 280, slide should be a 4 (Not 3), pilot jet 30, needle jet 389/063 in the middle position (3), needle jet 106, no letter at all for the needle itself.  David Stein  4/20/09

Sealing Inlet manifolds: If using the stub-mount carbs, I use a bit of plumbers teflon tape. Fuel resistant and very thin and you can apply as many layers for a nice snug fit before clamping. Prior to switching back, I had flange mount and would just use some wet/dry paper on a piece of glass and true the surface by sanding the face.  John Romano  3/26/09

Amal 930's for Vincent Twins:  Here is the setup for 930's (30mm). >This gives 1st kick starts and perfect throttle response, with text book plug readings (Champion #120).  These are the late model concentric w/#25 pilot jets built in. Starting from the top: #622-122 throttle needle in lowest position; #3 throttle valve (slide); #106 needle jet (use the one with the cross hole in it; #180 main jet. set the pilot air screw around 1 turn open, then adjust to your bike's requirement. Set the throttle stop so there is a 1/16" gap at the bottom of the slide and adjust to your bike when warm.   John Ulver  12/16/08
Period Feridax Throttle Lock:  From memory I think it uses a Wilmot Breedon (or similar) car lock and the key could come from a classic car specialist.
I think the number is stamped on one of the castings - something with a two letter prefix eg FP256. I have seen  traders at Autojumbles with racks of the keys.
Chris Chant  7/23/08
Carburator Finish: Rear carbs, die castings in zinc alloy, were silver painted. Front carbs, sand castings in brass, were cadmium plated. Later die cast carbs weren't even painted.  Sunbeam 6/9/08
One option is to paint your carbs with Eastwood's "Carb Renew," item # 10187Z (silver).
Bev Bowen  6/9/08
Slide Sleeving:  Alverstoke Restorations in UK bore the body and resleeve the slide in brass to suit, about $80 and 7 day turnround. Plus Atlantic crossing presumably.  I've never heard of anyone using steel. But a common misapprehension is that the hard parts wears the soft. It's the reverse. The soft part holds particles of grit still while they wear the hard part away. A wooden brake block would last longer than the farm cart did. Replacing the iron tyres on which it bore kept blacksmiths in regular employment. It's the same mechanism on which the grinding wheel is based.  Sunbeam (?) 5/27/07

Comet 1949 - 1954
Carburetter type: 229F/1DV
Mix Chamber Body No.:229/112R
Internal Bore: 1-1/8"
Center line of body to face of flange: 1-1/4" dia.
Flange centers: Clip
Jet block part number:  220/069R
Jet block size no.: 58
Jet size no.  200
Throttle Valve: 29/3
Needle position:  3
Needle Jet: Std
Float Chamber type number: 64/154B
Spare parts list no.:  440          Doug Wood  10/4/07

 "Early" Shadow carbs, with the adjusters on the right side were 289M/1DO.

Carburetion and mixture adjustment at idle:  Correct  setting of  the  idle / low end air screw and throttle stop eludes many and is quite easy.  All  touring  British carburetors have their air screws built  identically,  i.e. where the mixture is rich one backs out the screw, and when it is lean one enrichens the mixture by  screwing it further in.  The general starting off  position is approx . one and a quarter turns out from lightly seated.  One starts and warms up after setting  it  so,  running the motor for a period of  but a few minutes - or rides around the block to normalize temperature and cylinder function,  and then returns,  and working  rather quickly with the bike on it's center or rear stand you begin by lowering the throttle stop screws until  you acheve a reasonable idle speed,  and then screw in the air screw slowly from it's general setting of 1 & 1/4  turns out - going in slowly.  Note the sound of  the exhaust beat, it will begin to slow and weaken as the  screw is turned inwards towards bottoming out.  Noting that,  you begin to screw it out listening to the beat speed up, - at a certain point it will be heard to reach a peak - the quickest point before once again beginning to slow and  falter.   Stop there and turn it back inwards and hear it pick up speed as the screw is turned inwards.  Find the peak position where it  runs the fastest / hitting the hardest .   Stop.   Now turn it a little further In { about 1/16th. to an eight turn inwards and  Stop.  That's  " slightly Rich  from peak ",  the position and  mixture condition  sought for smooth  running  and easy starting.   At the finish of  this entire  procedure you will  find it fairly close to this position,  but  most  motors will vary a bit  here to acheve  sweetest running.  Stop the motor and let  her cool down.   Never prolong the idling period as the results of  this work will be poorer,  and  motor damage can result.  A  Warm -  Not  really Hot engine gives the best  results. Use of a  fan blowing across the motor and pipes is a good idea to lessen chances of  blueing or overheating .    After a quarter hour of  cooldown,  restart and you  find the idle speed is higher than desired.   Back off the throttle stop until  it allows a more normal  idle.  Then repeat the earlier procedure once again seeking  the  air screw position which suits the new slide position.   This will go quickly,  and then try  easing off  the throttle screw just a bit more to see if  it will accept a bit less  and still give a nice reliable and steady idle.  Whenever the slide height is altered downwards seeking a slower idle beat  it's normal that the mixture screw can  be   adjusted a tiny amount to better the results.  Once set  it will seldom need but the slightest  tweak,  usually a little inward for Winter conditions and outwards for Summer.    All this describes the proceidure on a British  single like a  Vincent Comet,  and naturally working with a  Twin  will require some thought and  consideration  for the second cylinder,  but the technique is identical.   After both carbs are set to acheve equal beats, one only needs to sync. the slide lift off   between the two.    With some practice you will develop a  keener ear and  touch, and it will  help identify which cylinder is  leading {firing  harder} by  momentarily lifting off one plug lead after the other -  listening  to only a  few  beats{ 2 or 3  is enough } to gauge which  is lagging behind thus needing a tiny  bit  more throttle,  and which neads a little backing off.  Thus you will balance the two.   Re-sync the liftoff  after this balancing  act.  Another trick is to stand at the rear behind the  bike and listen to the idle beat from the muffler -- as with a long  slim screwdriver you slip in beneath each slides cutaway - and gently lift the slide a few thou whilst  noting the change in the beat.   First one and then the other.  This will reveal which cylinder is hitting harder and which is being dragged along doing  little work.   Seeing what is needed to balance the effort you ease off on the stronger cylinder and bring up the weaker.  Very little tweaking will be needed to acheve what is desired.   Mind you - don't  let the old girl get too hot,  she won't  like it,  and might punish you for doing so.  All of this is really an art if  you get good at  it,  not  wrenching .  And is near to being a lost one.   Sid Biberman  3/15/08
Amal jets are sized by flow rate. As an example, a 180 jet flows 180cc per minute with a set head of fuel. I don't know what that head is ( a tank of kerosene 1ft (12") above the jet normalised to 21 Deg C) a nd the flow rate is measured in cc per minute as it was all done at the factory. No doubt it could be back checked by setting up a marked jet and increasing the head until it flows the marked amount.   Phelps  12/20/07

Tuning and Jetting Guide For Amal Mk.1 Concentric Carbs on Vincent Twins, and Singles.

There are (3) major components to the proper setup of Amal Mk.1 Concentric carbs when used on Vincents. These are: 1) Carb Modifications, 2) Carb Jetting, and 3) Ignition Timing. Each will be covered here in great detail.

Amal Mk.1 Concentric Carb Modifications.

New Amal Concentrics can be purchased today from several sources, and sometimes, they can be bought equipped with the jetting that you will specify. Regardless, these carbs whether new, or old/used need to be "blue-printed" for use on a Vincent. I learned the hard way that they CAN NOT be just mounted, and used. I found data on the proper setup of the float level. I discovered that a restrictor low speed orfice must be drilled out, and I discovered that the brass fuel feed nozzle in the bore needs to be modified (like a Norton 850' 932 carbs). Perform all (3) of these mods!

1) Float Setting: Normally the float in NOT adjustable. The float's needle seat that is in the float bowl can be moved slightly up or down to the precise location by first running very hot tap water over the seat for a few minutes, and then gently tapping the seat in either direction to move it. Use different sized rods, or drill bits in a manner that won't hurt the delicate needle's seating surface. The proper float height is .080" measured from the top of the float to the top edge of the float bowl. It is important that the stock bowl gasket be used because of it's specific thickness. To measure for the .080", assemble the float, float pin, and needle into the bowl, and carefully hold the float pin fully down as if it was installed to correctly position the float, hold the float level, and upright as if it was on the bike. I use a .080" drill bit, and I lay it on the top edge of the bowl near the float (opposite end of the float from the needle), and I "eyeball" the thickness of the .080" drill bit, and compare how far down the float edge is from the bowl edge. The float drop should equal the thickness of the .080" drill bit. The seat will need to be heated, and moved several times to get this adjustment just right. If the float level is too low, the carb will always act lean, and if the level is too high, the carb will always act too rich!
2) Low-Speed (Pilot) Jet Restrictor: The Low-Speed jet size for a Vincent is very important, and on the later Concentric carbs, a restrictor jet of about a #15 jet size is installed that limits the available low-speed jetting size. This size is only applicable to 500's! On the side of the carb is an angled screw for setting the slide height, and a horizontally mounted adjusting mixture screw. Remove the mixture adjusting screw, and spring, and look into the hole it came out of. You will see a restrictor jet with a very small hole (.015"). This will need to be drilled out with a .040" tiny drill bit. Great care must be used while doing this to not wreck the carb, or to break off the end of the drill bit! Now this restrictor is equivelant to a #40 low-speed jet (larger than you will ever need). Now, the normal low-speed (pilot) jets can be screwed into the carb body's pre-drilled orfice above the float bowl. A #30 Low-speed jet is correct for most Vincent applications. A general rule for selecting the correct low-speed jet is that the fastest idle speed found by adjusting the mixture needle while idleing should be found with the needle out between 1 to 1 1/2 turns out (prefferably 1 1/4 turns out).
3) Brass Fuel Feed Nozzle Modification: The brass fuel feed nozzle visible inside the throttle bore (the needle goes into it also) has a round cylindrical design where it stands about 1/4" above the bores lower edge. This is appropriate for small displacement motors, but for larger applications (like a Norton 850, and Vincents) this feed nozzle needs to be modified. When you look into the carb's bore you can see this feed nozzle. The complete back half (downstream) needs to be cut away. To do this, carefully scribe a mark along the lower rear edge of the feed nozzle along the body's bore surface. Mark a small dot with a "Sharpie" pen to orient the exact midpoint of the rear of the feed nozzle. Disassemble the carb to remove this feed nozzle. Carefully mark the sides of the feed nozzle with vertical lines for cutting away material. You want to use a Dremmel tool with a cut-off disc, and be very careful to remove exactly 1/2 of the feed nozzles exposed material (the rear half!!). Re-assemble the carb. The need for this is because at low engine speeds with only slight throttle (slide) opening, the in-rushing air will pick up fuel from the needle while air is rushing around the feed nozzle, rather than the air having to rush over the top of the feed nozzle. Untill I discovered this mod, I was suffering poor low end running, as well as alot of detonation, and heat build-up.

Jetting Guide For Amal Mk.1 Concentric Carbs For Vincents.

As you know, not any (2) motors, and their operating enviroments are going to be identical. These jetting guidelines should either be correct for your bike, or at least be within one jetting change from correct. Careful observations, and adjustments must be made after an initial impression has been realized. I have discovered some things that may influence other bikes. One is the size , and flow rate of your pet-cocks. These are bigger carbs, and under hard riding, they may need more fuel than your pet-cocks were flowing before. I have had great success from the late Norton style pet-cocks with the "paddle-type" lever. Don't get the cheaper Taiwan units. Spend the extra money, and get the much better British made units! Pet-cocks can definitely affect your main jet size!.

Jetting Specs:

1) Slide: I like the 3.0 slide for quicker throttle response than the standard Amal 3.5 slide. Use "hard-chromed" slides if you can find them. The last ones I found were at (Clubman Racing). The "Pot-Metal" standard style slides just won't last as long, but they work great.
2) Needle: I use the standard Amal needle with (3) needle clips. I've found the middle notch to be best for higher elevation, and in some cases, the lower (richer) notch might be best. This is a very subjective setting, where you will need to drive test each setting to find which feels the best. This setting affects the feel of normal "inner-city" type acceleration (not high, or low speed running).
3) Needle Jet: The standard size needle jet is a #106. I have had better success with a richer #107 needle jet. This adds a tiny bit of richness to the mixture at idle, just after idle, and everywhere along the needles taper. This increase was very beneficial to my Vincent as well as my Norton 850. I have found that it is easier for me to remove my bowls, and upsize a needle jet instead of removing the carbs to change a needle clip position when going from my home at 7,000" elevation to sea level. Often people are changing low-speed, and sometimes main jets to cure a mid-range jetting problem, where a change in the needle jet was the only cure. I've found that bikes that ran fine decades ago on older style fuel usually need an upsize of at least one size for the needle jet to react to today's newer fuels. I've found this to also be true for my Mikunis! What people don't tend to realize is that the relationship of the needle jet orfice to the needle's shank diameter is actually another jet size! This relationship affects the jetting from idle to just under full throttle.
4) Main Jet: I have found for a basic Rapide, or Shadow motor that a #220 jet for higher elevation, and a #230 jet for sea level works best. This size may need to be adjusted if you are running straight through muffler, velocity stacks, hotter cams, etc.. I use #250 jets in my 1,164 cc "Big Bore" motor with Mk.2 cams, 10:1 compression, and a straight through muffler.
5) Low-Speed (Pilot) Jet: I found the #30 Low-Speed jet to be correct for a basic Rapide or Shadow motor. I am using a #35 jet in my "Big Bore" 1,164cc motor.
6) Float Level: The float level at the top edge of the float measured at the dge away from the needle and seat should be .080" below the top edge of the float bowl. This has been covered above!  Jim Mosher  11/29/07  (Jim designed and sells Concentric manifols for Vincents at ....seems like an OK guy.  He also posted an excellent complimentary article in the Vincent Tech Section on Magnetos.) 

I'm running 32mm Concentrics on F10AB/1/399; #3 slides , Needle clips in center groove, needle jets #106, main jets 230, pilot jets #30. With 2500 miles on a fresh engine, it starts easy, idle is great, will go over 100 mph (once, according to chronometric speedo, impulsively, with suspension and brakes not fully set up) @ 35-37 degrees advanced timing with a BTH magneto. 50mpg average. Plugs read  rich which is a project currently underway to correct.  Jack  9/15/07
Mixture: 1) mark the throttle at fully closed and at fully open. Then you'll know whether the trouble is slide (0 - 1/4 open), needle (1/4 to 3/4), or main jet. Main jet affects both, but sounds as though you have a flat spot.    2) I'm running 190 rear 180 front with no filters. The rear is pretty good, the front masked by oil but there are no holes in the piston, so I think they're both good. Unless the K & N filters have no impact on airflow, you ought to be weaker than that.   3) If you can hold the throttle at the flat spot and lower the air lever s-l-o-w-l-y, if the problem goes away before it gets much worse you were too lean, if it gets worse before it gets much worse you were too rich..  Roy Cross  6/19/07

If the mixture needs a little leaning out there are two easy ways.   Place a tiny washer UNDER  the needle jet -  lifting  it higher up the needle. Fit an extra fiber  washer {thus two}on top of  the float arm , one below .  This will lower the float level.   Also you can slightly rotate the spigot carb. on the manifold stub to lower  the float level .   Sid Biberman

Idle Mixture Adjustment: While its easier to  hear and feel on a single  like a Comet --  the  air screw is slowly backed out from snugged in by about  1 and one quarter  turns .  As it leaves its seat  the motor speed will begin to tick over faster and reach a peak at that no. of turns  approximately,  each motor a little different .  Somewhere between  one full rotation  and  a bit past another quarter  it will begin to drop off again ,  at that  point  stop ,  and go  back in  a bit .  Ease off the slide screw  to bring down the idle revs to a nice even  beat ,  then repeat  the  air screw  dance  to see if it has changed its needs  and re-adjust slightly  the same  way .  The rule is  this  , the highest  peak you reached is  slightly too   lean to start easily --  so go back in slightly  richer  , ie .  "   just a bit rich off the lean peak "  .    OUT  is leaning it out ,  IN is  going richer .           This is an art , not a science  and more difficult  on a twin due to the other cy.  firing  .  Takes practice  and a good ear .   Do it  on a warm motor , NOT  on a really  hot one as the  rising heat  gets the  liquid fuel to perculate  and  messes up the process .   Dont  let her idle too  long  and get too hot .  Get it done    in  as short a period as  practical for you  and  not being  harmful to the motor .  Prolonged idling can cook the rings  and piston .    On a twin  you can lever up on each slide in turn with a spoke and tell from the beat which is hitting harder ,  then back off a tiny bit on that one  and raise the other slide  till they  sound the same  at the  tail pipe .   Good Luck .  Sid .
If the
float is not  distorted / crushed or full of fluid,  and if the needle is correct  pattern and not  had its slot altered  then the level should be correct  or nearly so .   That  is if the bowl itself  is the correct one.   If there is a reason to suspect  the mixture  is rich or  lean then  this  can be acertained  by  raising or lowering the float bowl by placing an extra washer on top /or below  to effect a height change.   For a fast check just rotate the entire  carburetor around its stub fitting to lift or lower the contents within.   Sid  (8/8/06)
There is a quick way to check
float levels check to do this without removing the float bowls. Check and adjust the level as normal; then modify a spare drain plug to accept a clear flexi hose - something along the lines of the windscreen washer tubing, only gasoline resistant. Then it's just a question of fitting the modified plug and raising the tube to above the fuel level in the bowl. The fuel should find a certain level. You can either scribe a mark on the bowl or measure accurately down from the gasket face and record in your service book. Granted the centre carb isn't the easiest to check but with a touch of trial and error... If you modify three plugs and fit simultaneously, you can use longer hoses and compare both levels. Next time you think the levels are out you can at least check both without disturbing the carb settings.  marc  8/8/06
Yes, theAmal 276/289
jet blocks are handed, there are two things different, one is the smallest hole on the edge adjacent to a larger air hole, the other difference is more obvious: there is a scallop out of the top to allow the idle screw to pass through. I reckon if you got the idle screws in you got the jet blocks in the right bodies. I have just tried swapping some handed jet blocks in a pair of 289's and can confirm you will not get the screw in if they are the wrong hand!  The 276's are handed, I think the early twins had nearly identical 276's so that the pilot air bleed screws were on the same side.  But the later ones had them on the opposite sides.    Roger Sparks  4/25/06
Amal Repair Work

AKA Lund Machine Compamy has gone out of business (retired) and sold to:
Andy Harden of AMAL SLEEVE Co.
800   295-2915
21502  99th Avenue S.E.
Snohomish, Washington  98296   USA

Concentrics: If any one is using or wants to use these carbs, here is the setup for 930's (30mm). This gives 1st kick starts and perfect throttle response, with text book plug readings (Champion #120).  These are the late model Concentric w/#25 pilot jets built in. Starting from the top: #622-122 throttle needle in lowest position; #3 throttle valve (slide); #106 needle jet (use the one with the cross hole in it; #180 main jet. set the pilot air screw around 1 turn open, then adjust to your bike's requirement. Set the throttle stop so there is a 1/16" gap at the bottom of the slide and adjust to your bike when warm. John Ulver  4/4/05

Mikuni heaven:

Mikuni:  For VM 34's on a standard Vincent
3 1/2 slide
159Q5 needle jet
6FJ6 needle
210 main jet
30 pilot jet
#2 air jet
Needle in middle position
float arms measure 22-24 mm from casting ridge      Robert Watson
Slides: A couple of weeks ago at the Urshel emporium Mike showed me an original 289 slide that he had sleeved several years ago in England to fit a bored out body. It was superbly done. Does anyone know who might have done or is doing this work? The reason I ask is that the slides that I have had made for bored out bodies become sloppy after a few thousand miles. We suspect that this is due to them being machined out of a single stainless blank and there is a tendency for the lower ends to contract towards each other facilitated by the two wide slits up the sides.

We did a little experiment. We measured the diameter at the top and bottom of an original slide (virtually unworn),  the sleeved slide in question and my stainless machined slide with three thousand miles on it. In the case of the original and the sleeved slide the diameter at the lower point, just above the cutaway, was actually slightly larger than at the top by about 2-3 thou. In the case of the stainless slide it was smaller by 4 thou.

Both the original and sleeved slide were of brass, (in the latter case we don't know what the sleeve material was). Could it be that Amal deliberately built into the design a slight differential in diameter so that the lower slide edges were always under slight tension against the body ensuring a good seal?

Experience has also showed us that when you mechanically widen the diameter, by carefully prizing the lower edges of a slide apart a little, the brass will retain this new attitude allowing you to get several thousand more miles out of it . However a stainless slide will return within a short while (days) to its original attitude as if it has a "memory", this in spite of the fact that the stainless slide is at least 10 thou wider in wall diameter. Tim Baldric  4/3/03

CV Carburators: Everybody  who experiments has concentrated on high efficiency carbs, like the TT/GP's, flatslide Keihins or Mikuni's, or round slide Mikuni's--or even Dellorto's.  The bad rap on CV carbs is the flow is less than optimum because of the butterfly valve in the airstream.  The benefit is that since the slide opening is responsive to vacuum from the intake, the mixture should always be perfect.  It's a "demand" system.  Even with shelves full of high-performance carbs, I've thought seriously of trying CV carbs on a Vincent engine.   Despite appellations like "the Beast," your post-war engine is in a relatively mild state of tune, and requires neither the lightning  response nor the enhanced flow characteristics of the best of the competition carburetors.  If your Vin is in a relatively standard state of tune and displacement, I wouldn't recommend a bit over 34mm bore, even with a CV carb--and maybe not even that large.

For example, if you have done any cleanup in the ports and have 9-9.5:1 CR and MkII cams, up to 34mm could be OK (given the poor top-end airflow characteristics).  But the lovely thing about the CV delivery is that you will find a smooth operation no matter the speed range or demand you place on the carbs.  John Caraway  12/14/01

Synchronizing Carbs: The one thing to remember is that with the one cylinder inoperative , with the removal of the plug, and maybe the plug hole open. Is that the back pressures will not be functioning as normal, and you will NOT get the setting correct.  If you want to find out more, try setting the carbs up with vacuum gauges, and you will find that when you adjust the throttle stop on one carb, the gauge on the other cylinder moves. I would say it`s almost impossible to get the carbs synchronised , by any other means than with gauges.   Trevor  04/24/01

Regarding where to sleeve carbs in the USA:     Mike Gaylord does Mk l Concentrics at 360 456-1425;  Walt Lund machine does Type 6's and Monoblocs at 520 790-9875.   Carl Hungness  04/19/01

Many leaky float problems on the 27's & 29's are caused by  poor fuel shutoffs and short side stands. Remove the fuel lines from the shutoffs and there should be no, I repeat no fuel dripping.  The standard sidestands lean the Vincent over too far, on the left stand the rear carb. will drip until the the fuel level drains off from the float chamber  through the bleed hole in the jet block, because the level in the float just got raised above the hole, and then out on to the back of the engine. On the right stand it's the same for the front carb., except that it drips on to the primary case.

If the fuel taps aren't dripping , then dip each needle in Brasso and give each seat a rub. Then extend each side stand 3" so that your bike will stand up straighter.To prove if it's the stand's fault, the carbs.shouldn't drip when the machine is on the rear stand.
To go the extra mile I machined an "O" ring groove in the needle of the front carb. right where it seats, after installing the "O"ring I then ground it flush with the tapered needle.

The rear needle, I shortened, and drilled it so that a Mikuni float needle could be snapped on to the end of it. This then required boring the old seat out and making and pressing in a seat that matches the new needle. They still drip! So! One minute before you plan on stopping, turn off the fuel, this will lower the fuel level enough to stop the dripping. Thats what I do.   Dan Smith  03/09/01

I bought a K&N "high flow" air filter, was told by my friend, Dynojet and K&N that the reason for my performance accelerating was because of the weather. Thanks to my wife for having the same bike, just stock and running better, they were wrong and many of you on this forum were right.  I broke down this week and moved the needle to 3.5, which did little and finally the 4th notch on the Dynojet needle. The bike not only is responsive but very smooth, no on/off rocking, no lag in thinking about accelerating, etc.

Many of us bought the K&N a month or two ago and I'm sure someone, other than just me, will have the same problem. The forum discussed how a "higher flowing" filter would require adjusting the carb. Take note The K&N may require a needle adjustment, but the adjustment may make your bike the best it's ever been. I still can't believe they market this air filter as "high flow" but insist carb changes are not necessary.  Pascal  02/15/01

Float needles as originally fitted to Amal Monoblocks and Concentrics were solid one piece nylon needles.  In response to reports of dripping and seepage past the needle, newer up-graded needles( the Viton  rubber tipped version) were later offered as an extra cost option. About the same time Amal described a  modification to both tapered needle and needle jet holder which quite transformed the running of the Concentric. The long needle now had 3 circles about its upper end and the jet carrier was longer in its lower portion.  A  reminder was made concerning the little brass hood situated in the base of the choke - that the 4 stroke part was cut off straight across its top while the 2 stroke version was cut off across its top at a steep angle.  Many complaints of mixed assembly between body type components resulting in poor tunning have been received at Amal. The motorcycles ran  poorly and were a beast to start !   I found this mix-up on a BSA 441 that  was a pig to start. After correcting the mismatched pieces, starting became far easier,  low speed running far improved, and roll-on power increased. If your motorcycle runs like a pig have a look inside its carburetor !  S.M. Biberman

Beware of Vitron tipped carburator needles if you are running on unleaded petrol.  I bought a new Monobloc carb for my Comet and couldn't understand why the needle stuck in the closed position after every ride.  A friend then advised me that unleaded petrol reacts on the vitron.  Since changing back to an old type standard needle I have had no more trouble. D.J. Peters 01/18/01
I think what you are referring to is actually Viton without the r. I also suspect that the problem with the carburator needle sticking is more likely that it is a mechanical wedge into seat than the rubber sticking.  Dan Smith cut o-ring grooves in his type 29 remote float needles and put o-rings in them and then ground them to the taper leaving them just a 1/2 thou proud and they stuck shut every time.  In frustration he ground them flush and ta-da, they worked perfectly.  One of the only rapides running original carbs that
don't leak when you leave the taps on and put it on the side stand!!  Robert Watson  01/18/01
I made a pair of flange-to-flange adapters for MK I's.  Here's how I did it.

First I polished the necked-down portion of a pair of standard adapters.  Then I made a pair of flanges that were a few thousands undersize.  With the adapters temporarily mounted to the engine, I put some alignment marks on the adapters and the flanges so I could install the flanges in the proper orientation.

Next step...put the adapters in the refrigerator's freezer compartment and the flanges in the oven at about 350-400 degrees F.  Place the hot flange on a flat surface (such as a smooth block of wood) and plunge the cold adapter into it.  If it won't fit (which mine didn't on the first two attempts) polish the necked-down
portion of the adapters a little more.

Repeat the heating, freezing, and plunging steps until you can get the adapter to bottom out in the flange.

Mine work perfectly--a complete seal was accomplished.  Someone with a milling machine can make the holes for you to the kind of precision required.  Just have them drill the two mounting holes and bore the center intake passageway.  You could also get them to mill a good flat surface on one side.  Afterwards you can cut them out with a hacksaw and file the edges to match the flanges on your MK I's.  A few VERY careful strokes with a flat file will assure a good mating surface if the adapter went slightly past the milled surface.

Without going out to the shop to measure the thickness, I would guess mine are about 1/2" thick--it was just
a scrap of aluminum I had on hand.       "Jay"  9/14/00

Mikuni Modification by Bill Easter  6/28/00    A number of people, Glenn Shriver and others, are using Mikuni VM carburettors on their Vincents and some would like to use cable start (choke) on the smaller 28 mm instead of the lever mounted on the carb. Here is a suggested modification to the cable start parts which I have not tried yet.  The problem is that the vertical space for the piston and spring in the 28 mm and smaller carb. is about 0.225" less than in the 30 mm and larger carbs.  The diameters and thread sizes of the parts are the same.  I suggest boring the bottom (threaded end) of the threaded cable start fitting 0.225" deeper so that the spring can go into it this much further and shorten the cable adjuster by 0.225".  Turn the full length of the top of the piston (slight smaller diameter of the piston and portion with slot and hole for cable nipple) down to 0.260" from 0.293" so that it will go into the threaded fitting.  This will also require that the cable end nipple be reduced in length and possibly shaped/radiused at the ends.

 Hylomar for leaking carb washers.  As I happened to have some of this already, and the data sheet states it's completely gasoline-proof, I decided to try it.  I soaked new fiber washers in Hylomar, coating them completely, and also applied it to the threads of the various fuel fittings.  On reinstalling everything, it seems to have done the trick - no visible leakage!  I haven't given the system an acid test yet by going for a long ride, but it's way more gasoline-tight than it was before.  Also, Hylomar is neat stuff - it's non-setting, so you can smear it about pretty freely and then wipe it off anywhere visible when you're done.
5/22/00  VOC-Jtan

Time for a few comments from the Western Canadian contingent about carbs, piston holes and the interconnections in life!!

I have run original Shadow carbs on the Woolly and when I went up to 9.4:1 I also went to 34 mm flat slide Mikunis.  The carbs were new and jetted very rich, like 25 MPG rich.  After many tries and 3 seized pistons I got the jetting really close and no more holes. I am now running HD electronic ignition and with no suitable timing device installed have set my timing by ear- like advance till you detonate and the just back a bit.  Good enough to run mid 7's at Ramsey and also give a real good thrash around the Island.   Many times I hear people with pistons holed who immediately blame the pistons but I feel the holed pistons are the result of the problem and not the cause.  I must agree with Sid, for who am I to disagree, that you need to look at  mixture, ignition advance, and fuel supply problems long before you blame a piston.

I know of one such piston being blamed and yet running over 40 degrees advance!  My experience says if you are getting more that 55-60 MPG on a nice 65 MPH cruise for a full tank then you are probably too lean.  Don't assume when something breaks that it is a problem all by itself, life doesn't work that way.

By the way I recall some suggestions about Mk 2 concentrics and jetting some time ago.  If any one has them could they send them to me. It seems a Twin recently arrived here is running rather rich and has a brand new set of Spanish Mk 2s.

And a note for Nick Cleary.  I'm not promoting and I know some may disagree but, making reference to the above, Danny Smith ran Kemp's pistons on his 30,000 miles plus travels to the tip of South America and then up to the
Yukon and they sre still just fine. Shadow type 29's, Mag ignition, and the addition of chrome top rings.  If you have the confidence that you are going to keep your motor together and not need to disturb them, put in good chrome rings, and hone the bores to the clearance recommended by the piston guys to the finish recommended by the ring guys.  With a good seal, no blow by, no oil leaks, no fancy breather (another of those blame the breather
when your leaky rings are pressurising the cases causing the leaks) and you should get a sweet running motor.   Robert 4/04/00

Holed Pistons:  Usually it is a mixture setting and/or restricted  fuel flow promoting a severely leathal condition . Also high on the list of causes would be excess ignition advance .  The flow fault is often as simple as a clogged  filler cap vent hole or fouled filter screens on the  fuel taps, or even not always opening both taps at sustained and  elevated speeds..

The early original cork taps are always suspect at providing sufficient flow for speeds above  60 -70  MPH  and  never for top speed runs .  Larger bore lever taps and opening out larger that cap vent is tops on the list for serious Vincent riders as would be closely setting ones ignition timing .  Incorrect  jet sizes, sticky floats, and inlet manifold air leakage at the male to female joint ( particularly that last one) are very common on older Vincents.    S.M. Biberman


 That reminds me of a time I was riding home on my Vin, one afternoon, in fast traffic, on a single lane in each direction road. I was running on the left side tap and using the right side tap as reserve. As luck would have it, she started to run dry going over a fairly long bridge. So I pulled out the right tap for reserve. And I mean, I pulled it out! It seems that the stop screw had backed out on me and was no longer doing its job.

 So here I was, going up a grade, on a bridge, with no place to pull over, with my petcock in my throttle hand, as I watched my reserve fuel poring out on my right boot and exhaust pipe, to the sound of my carburettors backfiring from lack of fuel.  To prove the old bromide about God looking out for fools, I was able to put the the cork carrier back in the petcock on just the second try, (I was wearing winter weight gloves at the time), and still had enough
fuel to make it over the bridge and to pull over and empty my boot of the excess fuel it was now holding.

 So to my fellow Vincent owners, don't try to top this. Please check those petcocks and think about an upgrade. ( I did, and I also put a little extra $ in the plate, the next Sunday).    Ken Smith   ( Phil. Pa. USA )

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