Topic: Won't return to idle RPM's

[vailjo]

1976 CB550

Hey whats up,

I've been experiencing a problem for a while and I'm not sure where to look next. My bike will idle fine at 1,200 but when I give it some gas, the RPM's will come down but stop at 3,000 and stay there indefinitely.

I recently changed my points, cleaned my carbs and synced them and checked my valve clearances and timing and still the problem persists. I'm just wondering if there's something I've overlooked/not looked at.

I'll admit that I'm a rookie to most of this and after reading some other posts I'm not sure how thorough I was when cleaning my carbs. I made sure all of the jets were clear, bowls were clean and air screws were adjusted properly but that was about all. Part of me suspects a vacuum leak but I've not done much to investigate it and I also think it may have to do with the vacuum and or emulsion tubes inside of the carbs.

Let me know if I'm on the right track or if there's something else it could possibly be.

Thanks

[70CB750]

I had similar issue and it was binding cable. But of course I have 1-4 cables.

[harisuluv]

have you tried adjusting your air screws?  was it like that before or only after you cleaned the carbs?

also, people are going to ask about your setup so you might as well fill us in on the details

[70CB750]

When it happens, shut her down and look in the carb from the airbox side. Chances are slides are hanging high - assuming your crabs have slides.

[vailjo]

This issue was present before changing all of these things and is still here

76 CB550
replaced airbox with pods
upgraded 4-2 exhaust (came with the bike, I think they were purchased from Honda)
Pilot = 38
Main = 100
Keihin 087A carbs
air screw at 1 3/4 turns

[vailjo]

In addition to all of this, I'm able to get the RPM's back down by letting the clutch out slightly then pulling it back. After i do that, the RPM's will go back to normal range and stay there.

[Retro Rocket]

replaced airbox with pods

Put the airbox back on and your troubles will disappear... Hanging idle is a classic symptom of pods and the cheaper the pods, the worse the problem. Honda's carbs hate pods for a number of very good reasons...

[phil71]

Poor carb sync can also hang the idle
.

[Rigid]

Induction rubbers leaking? Try spraying around carbs and boots wit starting fluid or any combustible spray.  Rpm goes up, or down, leak is found. I am betting on misaligned or binding linkage though as stated above.  Try pushing down on the lift arms, they will hang up if not aligned properly

[mono]

Mine does that too, although not that high rpms.  I just blip the throttle and she drops back down to 1100.   But i know i could use some new cables.

Sent from my SPH-L710 using Tapatalk 2

[dave500]

vacuum leak and or idle circuit too lean,like dirt somewhere,the advancer isnt sticking is it?

[70CB750]

If the advance springs are tired and stretched, you can shorten them half a turn.

[Lars]

+1 on vacum leak. Replace inlet rubbers from carbs to engine and tighten properly. Had same problem on a CB 750 to a friend of mine.

Original airbox and filter is best in my experience.