Motorcycle Repair: 76 cb 750 popping at idle, air screws, air screw

Question
hi i have my 1976 cb750 4 it lately has been popping at idle and im wondering if my air screw is lean or too rich? above idle it runs just ducky and is tuned in just fine ( timed and needle set ) i also have a kerker 4 in 1 exhaust on it if that makes a huge difference. i am at 0 feet above sea level, 55 degrees , and i have the old style kehin carbs. thanks. -mike

Answer
Mike,

with the kerker on it I would suspect
it is running a bit lean due to less
backpressure.

If it runs okay at mid-speed, you can
just adjust the air screws or increase the
idle jet size a bit to smooth out the idle.

Carb boots can leak which also
leans out the fuel mixture.

Has the valve clearance been checked?

Also popping can be due to leaking exhaust
header gaskets or pipe joints.
The air sucked in causes unburnt exhaust gases
to burn and pop.