High idle, black plugs after carb cleaning

[chefjosh]

I have a 1981 GS450 with about 11k miles on it. When I first got it this summer it ran well but had a fuel leak in the rubberized "T" fitting between the two carbs. I created a temporary fix to patch the leak since the fitting was over $20 and ran the bike for a couple months that way without any problems.

Well, the leak returned, as I knew it would one day, so I ordered the right part. Took the carbs off, replaced it, cleaned them up, put them back in, no more leak. However, now the bike doesn't idle right. It starts alright, idles alright, but then when I hit the throttle the bike shoots up to 3k and holds there. If I back off on the idle screw just a tiny hair, the idle returns back to normal.

If I have the bike set to idle low, around 900 to 1k, I don't seem to have the problem with it holding at 3k on throttle use. If I put the idle up to about 1200, I have the problem again.

I did some searching and it appears my problem may be an intake leak. I replaced the intake "O" rings with new ones. The intake boots seemed to be in good shape with no cracks, so I didn't replace those. There is plenty of slack on the throttle line and when the bike is holding at 3k the linkage that holds the butterfly valve open does not appear to be stuck, pushing it down with my finger does nothing.

Today I couldn't get the bike to start, pulled the plugs, and they were black. They were new last month. Got a new pair, put them in, rode around the block to verify my "holding at 3k" problem was still there. It was, and when I got back to the garage I couldn't start the bike again. Pulled the plugs, they were black after riding it under 2 miles.

Any ideas or things I should try? It is odd that this happened after I removed the carbs and put them back in again. Perhaps a weak ignition or some sort of adjustment screw in the carbs? Stuck float? These are things I've read about but do not really know enough about to speak well on.

[GS850_Coug]

You say pushing on the throttle linkages does nothing. I'm assuming you mean that the throttle butterflies don't move. Because adjusting the idle control changes the behavior of the problem, I believe there is a problem in the linkages between the carbs. Check that all the synchro screws are resting on the plate that fits from the next carb. That is where I believe your problem is.

[chefjosh]

Thanks for your reply.

What I mean was that I took a screwdriver and pushed down on the part where the throttle cable connects to the carbs, to ensure that the butterfly valve was not stuck in an 'open' position even though the throttle cable was slack.

I just pulled the carbs off the bike and did a bench sync by using two thin pieces of wire and adjusting the screw you are speaking of so that the wires have equal (to the best of my hands ability) resistance when pulled from under the butterfly valve. Both sides open and close at the same time and "click" in unison. Everything appears to move smoothly with no binding. Should that be all set?

Also I notice that it is only the "drivers side" plug that is covered in dry soot, which is easy to wipe off. The other plug appears to be much cleaner.

[chefjosh]

A friend came over this weekend that apparently grew up working on these bikes and knew a lot about CV carbs and various systems on my bike. He said my intake boots looked great and probably had been replaced before. He took the carb apart, used some fine wire to clean out some holes and did some general maintenance. Said the carbs looked good. The vac line between the carb and the petcock was a little loose at the carb end but we used some teflon tape to seal that up. He put everything back together, bike still had the same problem with it keeping idle at 3k once it's warmed up. Took it around the block and said it ran great otherwise.

While the bike is idling high we shifted the carbs around and pinched and prodded here and there to see if anything changed... nothing.

He took the timing system apart and noted that the springs on the mechanical advance were stretched a bit, perhaps making the weights not pull back in properly. He said he thinks that is the problem most likely. However, I cannot find the springs seperately, its part of a $120+ govenor subassembly.

Any more thoughts or ideas? I'm at the end of my knowledge rope here and really don't want to take a $400 bike to a mechanic if I don't have to.

[MGS450]

Try talking to some of your local bike mechanics they might have one laying around or maybe from another bike that uses something similar. Good luck

[rustybronco]

Thanks for your reply.


Also I notice that it is only the "drivers side" plug that is covered in dry soot, which is easy to wipe off. The other plug appears to be much cleaner.

problem appears to be with one carb.

He took the carb apart, used some fine wire to clean out some holes and did some general maintenance. Said the carbs looked good.

did he check the passages to see if they were plugged and check/set the float levels?