Topic: idle reving

[carl550k]

 as my cb550k warms up the rpms dont want to seem to come down at stop signs and red lights. just seems to hang at around 3000.the only way top get it down is the main idle screw, then it will barly idle .only does this when warmed up. any sugestions?

[TwoTired]

The CB550K was made from 74 to 78, and the later models have different carbs.  Knowing what year bike you have would help with a proper diagnosis.

But, in general, a cold engine requires more fuel to operate than a hot engine.  If your bike doen't have a knob choke then it also has no fast idle cam to hold the throttle open during the warm up.  You have to provide this with your wrist.  The main idle knob should be set while the engine is thoroughly warmed up.  And, until it reaches normal operating temp, you must have a choke setting and hold the throttle to a speed that maintains a run condition.

Fuel doesn't atomize as readily when cold as when hot.  These carburetors don't have any engine temp sensors like more modern, computer equiped vehicles.

You may have to just get used to it.  Unless there is more to the problem description than what you've posted so far.

Cheers,

[carl550k]

 sorry about the lack of detail. the 550k is 1976. it has kein hin carbs set at 1 1/4 turns out.it does need to be syncronized, has never been done to my knowledge.the bike has always had this prob, been in the family for 25 years.have been thru everything, carbs, valves, timing points,engine has new top end gaskets.also has anew uni air filter.

[migopod]

I'd synch the carbs first.  Mine used to idle at 3K or not at all until I gave it a good, solid synching.

[TwoTired]

Unsynched carbs can make idle speeds unpredictable.  But, I don't normally associate that with a warm up issue.  If you know your carbs aren't synched properly, then clearly that needs to be done.  But, note that synching carbs is nearly last to do.  All tune up items should be done first; plugs, points, timing, tappets, cam chain adjust, air fliter...  The pilot screws (and, perhaps, other mixture settings) are set as the very last item interactive with the idle speed knob.
FYI, the book values for pilot screw settings are only applicable for bikes with stock exhaust and induction components.