Idle increases intermittently when standing still.....

[interceptor44]

When I stop at a light or stopping and going in bumper to bumper traffic, my idle increases from 800-1K TO 1800-2K!
Not always but a lot of times. Playing with the choke sometimes calms it down but not always. Also, sometimes when I take off
it will idle down...thinking maybe throttle cable? '91 ST1100 18.5 K miles.....

 

[dwalby]

I don't have any first hand experience with this, but an intermittent vacuum leak is one possibility. Try spraying carb cleaner around the carb boots and see if the idle speed increases. It could also be a vacuum leak elsewhere, there's a fair amount of vacuum hoses in the system, but around the carb boots is the first thing to try. Another easy check is the vacuum line from the #3 cylinder (right rear) that goes to the fuel shutoff valve located next to the "gas tank" on the right side of the bike.

I'd only suspect the throttle cable if it happens when you turn the bars one way or the other, and you didn't mention that.

 

[interceptor44]

I don't have any first hand experience with this, but an intermittent vacuum leak is one possibility. Try spraying carb cleaner around the carb boots and see if the idle speed increases. It could also be a vacuum leak elsewhere, there's a fair amount of vacuum hoses in the system, but around the carb boots is the first thing to try. Another easy check is the vacuum line from the #3 cylinder (right rear) that goes to the fuel shutoff valve located next to the "gas tank" on the right side of the bike.

I'd only suspect the throttle cable if it happens when you turn the bars one way or the other, and you didn't mention that.

Ok, Thank You.

 

[Chris09]

I would guess [and it's an un qualified guess since I have never owned a thirty year old ST, in fact, I've only taken mine apart the other day, and...] that you've been driving around on this old bike [for like, a long ______ time,} thinking a couple of things; first, it's pretty good, just being me and the second is hey, it's a Honda, [how am I doin so far]

 

[Chris09]

... it's probably the idle jets and that garbage some people call gasoline, with the ethanol in it...
met up with my suzuki friend; can you imagine my suzuki friend; '75 I think it is, can't remember the year, anyways, it's in my - great japanese motorcyles - book [written in Europe] this guy is, I don't even want to ask him, lives in Richmond, pushes this heavy 750 out, fires it up, and off he goes; I never see him again until the next time I wonder if he's dead... or... will sell me that bike

 

[afrymoyer]

First place I would look is at the choke cable clamp/mounting point at the left front of the plenum. Remove the entire air box assembly and you’ll see the Phillips screw and pinch clamp. It is very common for the screw to loosen and have the choke cable pop out, keeping the enriching circuit partially open.

Have a real good look at the air filter AND the secondary air filter while your in there….

 

[TMF]

When I stop at a light or stopping and going in bumper to bumper traffic, my idle increases from 800-1K TO 1800-2K!
Not always but a lot of times. Playing with the choke sometimes calms it down but not always. Also, sometimes when I take off
it will idle down...thinking maybe throttle cable? '91 ST1100 18.5 K miles.....

If you are blipping the throttle at a light the throttle cable could be involved but that should be easily detected. My ST will idle up 1000 RPM or so when the fan cuts on going from 1200 to 1300 but returns to 1200 when the fan cycles off. There's a known symptom of lean running where an engine is very slow to return to idle. That problem is more likely to manifest when the engine is colder and running even leaner and would moderate as the engine warms. Lean running is often caused by degraded intake manifold rubber or poor fitting leading to an intake air leak. You could remove the faux gas tank cover and spray starting fluid at the manifolds (starting fluid because it won't leave a mess). If the idle changes you've found the problem.