Motorcycle Repair: cb350 k4 carburation, air leaks, advancer

Question
I have a 1972 cb350 k4 which is sluggish below 3000 rpm then takes off like a rocket at 3k. Why is this and how can I cure it? I have keihnin 722A's with new jets, float needle valves, 'O' rings, float bowl gaskets and have had the carb bodies sonic cleaned. the only jet not replaced was the slow jets as these were clear and the correct size .
Any ideas please.

Thanks
Alan

Answer
Alan,

Your bike should have a 26.0 mm float level, #68 primary mains and #105 secondary main jets, according to Honda Carb specs. If all of that is correct, check your carb diaphragams for any signs of pinholes or tears.

Beyond that, assuming you have about 175 psi in each cylinder, is that you may have a sticking spark advancer. Remove the point plate and check the feel/function of the advancer's point cam as it twists back and forth on the advancer base.

I would check the intake manifolds for cracks/air leaks, too. Ensure that both carbs are syncronized properly.

Proper valve clearances are .002" intake and .004" exhaust.

Bill Silver