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Idle Help

donmiller212

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Hello, I'm the new owner of a 72 CB750. The bike seems to be in good shape, with a lot of fairly recent work done, per seller, with receipts of items installed on the bike.
The bike will start with the choke lever up, a little bit of throttle, and will stay running with the throttle slightly opened, keeping the RPMs around 1200. If I let off the throttle the bike stalls. Where do I go from here? Someone recommended checking for seal leaks, but am I able to do this effectively if the bike won't idle? Other suggestions?

Thanks in advance. Recent work below.


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dirtdigger

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These bikes are not fuel injected, its old school, no automatic idle control to compensate for difference between cold and hot engine. You have to turn the idle up with the idle screw and adjust it to normal as it warms up. Also warm engine speed is 1000 +/- 100.
 

amc49

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X2, the engine is NOT supposed to idle cold while you have fully hands off. It should stay running to idle properly only when warmed up. Cold engine management is a rider developed skill.

An old school cruise control like a Vista-Cruise can be very helpful there to lock the throttle partly on and avoids having to mess with the warm idle speed at all.
 

donmiller212

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X2, the engine is NOT supposed to idle cold while you have fully hands off. It should stay running to idle properly only when warmed up. Cold engine management is a rider developed skill.

An old school cruise control like a Vista-Cruise can be very helpful there to lock the throttle partly on and avoids having to mess with the warm idle speed at all.

So I am completely new. How exactly DO i adjust the idle screw?
 

donmiller212

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So I figured out the idle screw. It still took about 4 minutes of light throttle to get it to idle. Once idling, I stopped using the choke and it held pretty steady at 1k. Outside temp is about 50 degrees f. All of this is pretty normal then?
 
Last edited:

amc49

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Yep, you should only mess with the idle speed screw once the engine is warmed up. People do it cold and then have to finetune it for warm all over and 10X too much work.

Why the cruise control helps, it preserves your warm idle setting to not have to mess with it at all. With cold engine you start it, set the cruise, then as soon as the engine gets slightly warmer the idle suddenly goes up more, you quickly readjust cruise again, you may have to do it 2-3 times but much easier than getting down around the motor to mess with it.
 
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