Amal Concentric Carburetor Overhaul

| 9/13/2012 3:37:18 PM

Amal Concentric Carburetor Overhaul 

There's an old saying that 99 percent of all carburetor problems are electrical. True as that may seem sometimes, the simple fact is, if your Amal carburetted British motorcycle isn't running as well as it should, a quick checkup and rebuild of the Amal Concentric carburetors might be just what the doctor ordered to get you back to running well.

Poor idling, uneven acceleration and misfiring can all be symptoms of a dirty carburetor or carburetors. Thankfully, Amal Concentrics — standard fitment on just about every classic British motorcycle built from 1966 to the late 1970s — are very simple devices. And that means cleaning them is easy if you use a little care. Depending on your bike, you'll have from one to three of them to clean, so the time involved can range from as little as a few hours to all day, with removal and installation often taking the longest part. That's particularly true with BSA and Triumph triples, where the gantry assembly used to synchronize all three carbs complicates the process.

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Once the carbs are off your bike you'll only need a few tools to do the job properly, including: a medium Phillips screwdriver for the screws on the top and the float bowl; a small flat-blade screwdriver for the throttle speed and idle mixture screws; and 8mm and 13mm wrenches to remove and replace the jets. You'll also want a gallon bucket of carburetor cleaner (with a parts basket to soak the metal parts), and a couple of parts tubs will come in handy to keep parts organized.

You'll also need replacement gasket kits equal to the number of carburetors you are cleaning, and it's usually a good idea to get new float needles, as well. As always, a good manual specific to your bike is indispensable, and if you don't have an Amal manual, Google “Amal Concentric Manual” to find one online — you'll want one for final tuning.

To get started, remove the air cleaner(s) then the carb(s) from your bike, using a 13mm wrench to unbolt the carb flange from the intake. On Nortons it's often easier to remove one carb complete with its intake stub, as the inner carb flange nuts are hard to reach with both carbs installed. Remove the carb top using a Phillips head screwdriver and withdraw the air slide and choke slide (if the choke is installed). If you want, you can leave the carb top with the slides connected and hanging from the cables and clean them with a rag and solvent, or you can remove them and dip them in the carburetor cleaner. It's often easier to just leave the cables connected, as disconnecting and reconnecting them can be a hassle.

12/14/2017 8:29:50 AM

When doing work on these British twins, Buy the proper Wentworth British standard tools. Your motorcycle will love you for doing so.

David Patterson
11/9/2012 11:45:20 PM

Be careful not to over tighten the mounting nuts when re-fitting these carbs. You only wish to squeeze the O ring enough to seal. Too tight and you can warp the body which can cause the slide to stick, usually at WOT.

David Patterson
11/9/2012 11:38:09 PM

They didn't. However,, it has been my experience that a 1/2" wrench is just a bit too tight on the banjo bolt and the jet holder. A 13 mm works fine.

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