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 | Sunday, July 12, 2026 |
Syncing Amal MK1 Concentric Carbs
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Many think of syncing Amal carbs as some sort of difficult dark art. It's not
actually hard if you do it my way! I never use vacuum gauges - if you want to,
then do it after following my procedure to the letter. It's easy to miss-adjust
things using gauges and make everything look correct. This is especially true if
not mechanically sync'ed first.
It is important that the floats (fuel level) are correct before starting this procedure!
I know this is non-standard, but it works 100% the time for me on every bike I build
or repair - I sync manually only. This is written for bikes with a junction box
for the throttle and adjuster on top of each carb. It works even easier for bikes
with separate cables to the twist grip and in-line adjusters.
Whenever reasonable, I do this on the bench with the carbs, cables, and twist grip
all connected normally - much easier, but it certainly can be done on the bike.
- Unscrew the throttle stops enough that they cannot touch the slides. Then while
holding a finger on a slide turn the throttle stop in until it just touches - you'll
be able to feel it. Then turn in 1 full turn. Do the same thing on the other carb.
- Adjust top adjusters or in-line adjusters until slides reach the top at the same
time when you twist the throttle (look in the carb and watch the slide edge reach
the top). On some bikes a mirror will help and on some it's best to have a
helper. This needs to be exact!
- With the throttle closed, while feeling both slides, slightly turn the twist grip
and see which slide moves first (if either). Whichever moves first needs its
throttle stop turned in slightly. Keep trying until the slides start moving off
the throttle stops at exactly the same time. This normally takes only a tiny tweak.
- Unscrew the carb adjusters until there is only a little play. This step is critical
when a junction box is used!
- Go back to 2 until no adjustments are made in 2-4
If done carefully, the carbs are 100% mechanically sync'ed and the cables are properly
adjusted.
Adjust the air screws to 1-1/2 turns out from seated. Start the bike and once warmed
set the idle to around 1100 making sure to turn the throttle stops exactly the same
amount. Blip the throttle. If it stumbles, turn the air screws in
slightly. Keep doing this until it doesn't stumble, or you are less
than 1-1/4 out. If you are less than 1-1/4 out, you probably have some other problem
like and air leak or worn slides.
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