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Erratic idle

malolo

CB750 New member
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Venezuela
Hi guys, after long years I ve finally got me a CB750 ohc, pretty beaten bike, I ll have to spend long time and effort to bring it up to shape. I finally made it run but the first problem I want to solve is that idle goes up and down. If I leave her alone it will keep it, but if I hit the accelerator briefly then it revs up and it s kind of hard to get it down again, sometimes pushing down the acc bar works, sometimes it doesn t, and sometimes it goes up and down by itself. Feels like an air leak issue but don t see where from. Can You guys help me in this one?
 
I would first spray the boots between the carbs and engine with WD-40 while it is running. If it runs better for a few moments then you may have cracked boots. Otherwise I would start going through the carbs (floats, float height, clean jets and idle circuit, pilot screw/idle adjustment, carb sync, etc.) to make sure they are all in spec.
 
Carb sync and make sure the ignition advancer is working properly and not sticking or weak advance springs.
 
Right on the money You guys. Thanks a lot. boots were leaking alright and some sinc was required after fixing. Had to make the boots out of radiator hoses and was hell to fit them in. Now the bike bike stalls strong when I gas her up but I think is just fine tunning. Thanks again
 
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