erratic idle

[650mark]

1980 xs1100sg, all stock and all original. starts/idles/runs extremely well, gets 40mpg. sometimes after a long ride the idle settles in at about 1500rpm, normally it's at about 1000. only does this after a couple of hours on the road.
I know that an intake leak can cause a high idle but wouldn't that happen all the time? also, could an intake leak at only one cylinder do this? thanks

[skids]

When you adjust idle, it should be at normal operating temperature.

[motoman]

1980 xs1100sg, all stock and all original. starts/idles/runs extremely well, gets 40mpg. sometimes after a long ride the idle settles in at about 1500rpm, normally it's at about 1000. only does this after a couple of hours on the road.
I know that an intake leak can cause a high idle but wouldn't that happen all the time? also, could an intake leak at only one cylinder do this? thanks

I know it may not seem related to you, but have you changed out the stock timing chain tensioner for one of the auto ones?

[650mark]

yes, I installed the acct several months ago

[motoman]

May wanna re-set the carb sync and idle mixtures.

[skids]

May wanna re-set the carb sync and idle mixtures.

Just to make clear, this has nothing to do with the ACC.

[650mark]

thanks. both were done after the acct was installed.

[DGXSER]

Just to make clear, this has nothing to do with the ACC.

I think Moto's point was that if the timing chain was not as tight before the swap in tensioners, then the timing would be ever so slightly changed and require synch and tune.

[motoman]

I think Moto's point was that if the timing chain was not as tight before the swap in tensioners, then the timing would be ever so slightly changed and require synch and tune.

+1................remember thirty plus yrs. ago that when my Venturer would get a bit of hang idle after riding some distance, the cam chain tensioner was due for a re-adjust. Of course that was prior to realizing it actually didn't really stay in place anyways.

[skids]

I think Moto's point was that if the timing chain was not as tight before the swap in tensioners, then the timing would be ever so slightly changed and require synch and tune.

I dunno, that seems like a stretch. (get it?)

[fredintoon]

1980 xs1100sg, all stock and all original. starts/idles/runs extremely well, gets 40mpg. sometimes after a long ride the idle settles in at about 1500rpm, normally it's at about 1000. only does this after a couple of hours on the road.
I know that an intake leak can cause a high idle but wouldn't that happen all the time? also, could an intake leak at only one cylinder do this? thanks

Hi Mark,
ah yes, the accursed "intermittent problem".
Try and demonstrate it to someone and it just won't happen until you are riding alone again.
Dontcha just hate that?
When the idle goes up to 1500 does it stay that way for the rest of the ride?
My best guess is it ain't the bike at all, it's the climate. Gets stinkin' hot down there, eh?

[650mark]

hi fred. you know, you could be right about the heat. this is like the toothache that disappears as soon as you get to the dentists office! and yes, the high idle speed stays that way through the entire ride. going for a 200 miler tomorrow with my local chapter of the VJMC and the temps are now back into the 60-85 degree range so i'll see if it happens again.

[KA1J]

Something I discovered when getting my Maxim-X synced and tuned was I would get a hang around 2K. It would stay there unless I put the bike in gear and let out the clutch slowly to drop the RPMs to 1K and then it would remain where it belonged till the next time the bike came to a stop and then the cycle would repeat. No amount of adjusting and playing with carb settings got rid of it. Even took the carbs apart to see if I missed something in my earlier rebuild but nothing changed after the 2nd time through.

What finally did fix it was when trying out ideas, I lowered the RPMs to around 800 & then loosened the linkage at the upper end by the grip till it was free of tension, then I adjusted the idle upwards to 1K but from the carb side. I don't know why having the upper adjustment loose would make a difference but ever since I've done that I haven't had a stuck throttle once and it always immediately goes back to idle.

Worth a try if nothing else.

Gary

[KA1J]

It would stay there unless I put the bike in gear and let out the clutch slowly to drop the RPMs to 1K and then it would remain where it belonged till the next time the bike came to a stop and then the cycle would repeat.

I see I didn't say something clearly. What I should have said was: It would stay there unless I put the bike in gear and let out the clutch slowly to drop the RPMs to 1K and then it would remain at 1K till the next time I would next rev the engine, then I'd have to do that again to get the engine to go back to 1K.

also

Sometimes if I waited long enough it would drop to 1K on its own but I rarely waited that long and if the bike was in neutral the RPMs were too high to shift nicely into 1st so I'd do that trick every time I came to a stop.

[skids]

It does seem like either it is not synched of it is running lean on one or more cylinders. A bad synch will make it rich/lean unbalanced between the cylinders. When you synched it, did you do it at normal idle with the bike warmed-up?