I had my Amal concentric carbs sleeved by Bruce Chessel of Woodstock ON – it was the best thing I’ve done for the bike. Sleeving the carb is actually a bit of a misnomer as it is the slide that gets sleeved, the body is just bored out and the slide is sleeved in brass to prevent galling from like metals.
I stumbled upon this service bulletin in a forum the other day and thought it worthy of reposting. My 750 commando is so thirsty at WOT that i need to open both fuel taps to keep the engine from stumbling – perhaps this will give a bit more top end?
Here’s a note from Dave Comeau (Atlantic Green Technical Services) when I was running 32mm carbs before I got the original 30mm Amals re-sleeved:
The ’70 model you show on your website, assuming it is the one with carb problem would not have originally been a 32mm. However that is not a big deal that they are not 30mm.
Your symptom of rough running at just off idle/light cruise is indeed….. cutaway.
Raising the needle will have more affect at bigger throttle settings.
If you have combat carbs with 3 cutaway, you will do better if you mod them to 3-1/2 or try them at 3-1/4 before you go all the way to the full 1/2.
IIRC each cutaway # is 1/16″ ,,,,,so a 3 cutaway is 3/16″
1/2 is 1/32″ custom 1/4 is 1/64″