Amal Concentric MK1

AMAL Concentric MK1 Carburetor  Re- builds.       By Tom Hesom

This is intended for those whose interest is in the restoration of British motorcycles fitted with Amal carbs, and directed more to machines built up from basket cases than to runners.  Much has been written about these often maligned instruments by more knowledgeable “wrenchers” than I, so I don’t profess to be an expert, but I have “fiddled” with the confounded things for long enough to have learned a few things, and continue to learn more.


For instance my freshly restored Triumph Bonnie would only run on one side until John T found that one carb had no in-body pilot jet! More recently more trouble with my BSA Lightning only to find that one spray tube was missing from one carb. The spray tube is the brass tube visible through the bore and like the in-body pilot jet is not normally removed as it is a friction fit and has to be tapped into place.


Most troubles by far however are caused by wear between the carb body and the slide.  Because Amals were built to a price dictated by the  always-cash-strapped British motorcycle industry, they used the same soft alloy material for both body and slide which they knew as well as anybody was conducive to fast wear. This wear causes all sorts of problems but mainly the inability to get the machine to idle because of excess air being drawn past the slide.


Only solution is to buy new carburetors,  but if  it is a twin carb bike this can be expensive.  New Amal MK1 carbs are available from Walridge Motors, Lucan, Ontario  @ $200 each plus shipping and handling. If you have a Monobloc or an even earlier Amal, they are also available at about double this price.  email;       Web


In my view a better option is to have your old carbs re-sleeved.  The bore is honed out to true and the slide is sleeved with brass.  This then obviates the same- metal problem and you have a BETTER than new instrument! (With the proviso of course that you also re-new any worn jets or needles at the same time)  I sent my carb bodies and slides to Bruce Chessell in Ontario by ordinary Canada Post. Bruce did a magnificent job in under a week and returned them promptly without asking for advance payment!  Said he would email me the price and return postage and I could send my cheque!  Rare trust these days!

Cost  $75-00 per carb = $150-00 plus postage $14-50 each way = $29-00    Total $179-00

Plus two Carb Kits (gasket sets)  # CGS900     @  $3-00 ea                 6-00

Plus two Tickler Conversion Kits  (no more gas on finger!)  @  $6-65 ea                13-30

Postage and Insurance                                                             7-70

Overall cost                  $206-00                             Bruce Chessell’s address;  314 Knightsbridge Rd,

Woodstock, ON

N4S 7C4                  Email;


PS   This price was even further reduced.  The Right-hand carb body had other problems besides wear in the bore and slide and could not be used for re-sleeving.  I put an ad in our newsletter and before it even came out Dave Pritchard said “How many do you want!?!”   and for no charge!   Thanks Dave!  One of the many advantages of belonging to a super motorcycle club!


Another Tip for Twin Amal Carbs


If you have difficulty getting the slides to rise simultaneously by a feeling finger in each carb intake and have no-one to operate the twist-grip,

– – Here is the answer;- – –

Put two 1/8″ drill bits shank first into the carb mouths just under the slide cut-aways. (with air filters off of course.) Two thirds of the bits should stick out and hang down slightly. Adjust the cable adjusters until both bits drop simultaneously when you crack the throttle.

This way you can get both slides to rise evenly on your own.  Then proceed in the usual way with both air filters back on, to set one carb idle  at a time by removing one plug on fast idle and adjusting on the opposite side until they run smoothly, then reduce the revs to a nice idle with both plugs in and both sides firing.


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