igya
Full Member
Posts: 81
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Post by igya on Aug 16, 2011 14:44:10 GMT -5
I can't find a thread talking about my problem, so I'll try my own. My '80 Mikuni 34 carbs are slow to idle down when I come to a stop. It takes about 5 seconds to reach idle speed. When I unscrew the throttle stop to a decent idle, it will quit in about another 5 seconds. When I set the idle to where it will stay running, it goes back to the "slow to idle down" mode. I've been through both carbs with a fine tooth comb, and everything seems to be good (but obviously not). This has me worn out man! Help would be appreciated.
p.s. The engine was running perfectly until I put its carbs on another 650 and started using this set from a different bike that's scrapped out. I could put the original carbs back on but then I'd still be short a set.
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Post by headcase on Aug 16, 2011 17:51:30 GMT -5
Might want to check the ignition advance unit to see if it needs lube or the springs are too weak to return all the way. I fought with the same thing for an entire season. I know it's not carb related, but just thought I'd give it a shot. There is at least one post in here with detailed pics on the subject, just don't recall exactly which one.
Dan
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pamcopete
Full Member
'78/E, '81/H, '82 XJ550, '74 CB750, '81 CB750, '73 CB450
Posts: 167
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Post by pamcopete on Aug 16, 2011 18:46:31 GMT -5
Well, "idle hover" can be either a carb problem or an advance problem, or both.
Here is a video of the how the advance mechanism should snap back if the springs are OK:
If the springs are weak, then the advance does not return to its idle position and the engine revs will stay high until you apply a load, like just letting the clutch out.
If the carbs are not synced, then one of them will be working at idle and not the other, except that the non working carb will "wake up" when the throttle is opened, causing the high revs, and then stop working again if you somehow reduce the revs.
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igya
Full Member
Posts: 81
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Post by igya on Aug 17, 2011 7:41:23 GMT -5
I feel like the advance is okay because it was working perfectly before the "new" carbs were installed. However, I never thought of an advance causing that problem but it sure makes sense. I'll make sure it's still in good condition. Who knows, maybe one of the springs popped off. Thanks!
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