Re: 75 CB750 wont idle with rebuilt carbs & no airbox

Posted by shinyribs on Jul 21, 2012; 7:25pm
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/75-CB750-wont-idle-with-rebuilt-carbs-no-airbox-tp4025625p4025628.html

I dont want to second guess your mechanics skill level,but it could just be a plugged or dirty idle jet. There could be something off with the tune also. Increasing the main jet will allow a slight change in the idle mixture,but minimal. I have a similar bike with pods and open exhaust. I run 125 main jets and 42 pilot jets. The idle mixture screws are out 1 1/4 turn,whereas the factory setting is 1 turn +/- 1/8 turn. The pilot jets and the idle mixture are key when tuning for non-stock intake/exhaust. The pilot jet is the circuit used to take you from idle to part throttle/cruise where the main jet starts to take over. More than likely tuning the idle mixture will cure your idling problem,but if you still have stock pilot jets then the bike will be lean down low. This will cause the bike to crackle and pop on decel and even some at idle.

I'd check the idle mixture setting first. Set it 1 1/2 turns for starters. It might be too much,but it will tell you if it is making a change on the bike or not.

The pilot jets will eventually have to be checked and maybe changed. But they are easy to get to without having to pull the carbs. Just pop the bowls off.