Idle slow to return

My bike ('81 GPZ 550) is very slow to return to normal idle after being revved(in neutral or under load). It will stay at 4,000 rpms or so and will take 10-15 seconds to return to normal idle or won't return at all. I synched the carbs a couple months ago. Then about two weeks ago I ran some GUMOUT concetrated carb cleaner through. Now it is doing this strange idle thing. I checked the carb manifolds for leaks using the starter fluid method, and no dice there. So what do you think is the issue? I'm going to go back and sync them again.

Thanks,
Nate

I would spray it all around where the head and cylinders meet. We just got done rebuilding my friends kz700 and tried using the same head gasket and it did this exact same thing. We sprayed ether around the carbs and found nothing. We sprayed it all over where the head and cylinders meet and found a leak. We then replaced the head gasket and it's good to go now.

Starting fluid "ether" is pretty dangerous to use like that, you would be better off and safer using carb cleaner or wd40. One loose spark coming off a coil or plug wire could make your bike a historical item,,
Ride and wrench safe.

Post edited by: The Milkman, at: 2007/07/14 20:50

Not sure I like carb cleaner which is pretty flamable. Use the WD40. Any leak will result in white smoke coming out the exhaust or the bike will die if the WD40 gets sucked in.

The problem may not be an airleak... If the orings on the airscrews are old and don't seal, this can cause the problem as can cracked vacuum caps. It is far more likely that the throttle return spring is tired or the throttle cables are adjusted without sufficient slack. You should see visible slack in either cable.

You can narrow the source of the problem by disconnecting the throttle cables and starting the bike and see if the problem occurs with the cables off the bike. If the problem occurs with the cables off, push down on the bellcrank which is the butterfly thing that the the cables hook into. If this immediately lowers the rpms and they stay down, it could be a mechanical issue (not an air leak) which will now be likely due to a weak return spring. This DOES happen and replacing with a stronger spring will help cure the problem.

Well I know it has been a while. I have resynced the carbs and the problem was still there. I checked for air leaks and didn't find any. Then I started to turn the air mixture screws out, and the problem has gotten better. However my question is what is the correct way to determine the proper position of the air mixture screws? What is the honda idle drop method?

Thanks,
Nate

Post edited by: Shoey949, at: 2007/07/24 16:04

You have the mechanical Tekei carbs, right? If so, an air leak would explain the slow idle drop but if there is no air leak, you can adjust the air screws till the cows come home and the problem will still likely be there. I have no idea what the honda air drop stuff is..., btw... sorry.

If you continue to have problems, and can't find an air leak, and have removed the throttle cables and STILL have the problem, the problem may be a weak return spring. Replace it with a spring that is made of heavier gauge steel. The slow return issue is fairly common on VM29 smoothbores where I suspect Mikuni originally used VM24 springs on SOME assemblies. If I am out testing one of those sets and the idle is slow to return, that is the USUAL problem in about 95 percent of the cases for a slow idle return. I am convinced that Mik used the wrong springs on some of them as they are the smaller gauge VM24 spring rather than the more stout VM26/28 spring. I just swap springs and the problem is fixed. I seldom catch the wrong spring when cleaning as they look almost the same as the larger diameter spring until you hold both types side by side.

That's the thing is that I have the air mixture screws at about three turns out right now and the idle is returning more like it should(good but not perfect). I was just wondering what the correct way to adjust the mixture screws is?
BTW they are the tekei carbs.

I have a ttr-125e and it did the same think. The mechanic said it might be a air leak

kg4kdn68 wrote: I have a ttr-125e and it did the same think. The mechanic said it might be a air leak

Welcome to the site kg.

This thread is almost 7yrs old and he hasn't posted anything in almost 5. I'd say he either got it fixed or sold the bike by now.