hello new to the forum had to join because I have a 1977 cb750 that has been very inconsistent I just recently synchronized all the carbs and cleaned them because the bike would lose throttle and die out but after doin that the bike ran good for a few days and now when I start it the rpm’s jump up to 4k with the bike in neutral should try to sync the carbs again? Or maybe float level is off I’m not to sure what would cause this even with the bike in gear it will go like I’m givin it gas. Anyone had issues like this before? Anything helps thank you.
What idle speed are you trying to get it to idle at? If the ignition advancer springs are getting weak and you have the idle too high, the rpm could rise as the ignition advances.
raising rpm is vacuum leak, lean mixture, advance timing issue.
raising rpm is vacuum leak, lean mixture, advance timing issue.
I would like to be at 1000 to 1500 rpm’s for idle I also just got done running through the carbs and cleaning them again to see if a float got stuck and noticed there was quite a bit of fuel left left inside where the carb boots bolt up. After cleaning them and putting them back on it hasn’t ramped up that high again. But I imagine it’s worth a look to check the timing again I just recently went through this motor completely about 6 months ago. I just have never had that problem before.
I will give the springs a look as well thank you for the response.
1100 rpm is max for idle. anything more than 1100 and you are getting into the timing advance. At 1500 rpm you are well into the advance curve as timing is all the way advanced around 2500rpm. If you try to make it idle anything over 1100 it isnt going to work, timing is going to be all over the place making the idle creep up as timing advances.
