idle up

[ScottsXS]

my new sf runs great, starts great, idles great.......except it idles where it is supposed to 1100 rpm +/- until it gets warm/hot after about 15-20 minutes the idle slowly raises up to 2100+/- what could be causing this by the way the bike has 6300 mi

[Ken Talbot]

When was the last time you sync'd the carbs?

[Mississippi]

Scott, Your engine has an air leak. (Sucking air between the carbs and the cylinder head) It sounds like it does not leak until it warms up and things expand from the temp rise. A good way to check for this is to run the bike until it heats up (I suggest using a fan in front of the engine to keep it from overheating) and starts ideling faster and then use some carb cleaner in a spray can (Berryman B-12 Chemtool is good) and spray small amounts around the vacume lines that go to the fuel petcocks and the ignition vacume advance vacume supply hoses and then spray each intake carb rubber holder. When you spray the area where it is sucking air the engine RPM will rise. Hopefully it will be a vacume hose leak instead of a bad carb holder. Good luck, Harold

[Dragon Tamer]

Hiya Scott,

I will go with Ken on this one, out of sync carbs will cause very erratic idle on these engines. A vacuum leak usually will cause a low idle or a miss below 2500 rpm.
This may be as simple as not getting the cold start mixture control (choke) all the way in after the engine has started and warmed up. There are three locations for the lever, all the way out for cold starts, center position for warm up, and all the way in for running. If you did not get it all the way in your engine will want to idle at around 2000 or more after it is warmed up!
Incidentally, do NOT spray a flammable liquid on a running motorcycle (or any other) engine!!! If it should catch fire it will be about impossible to put it out in time to save the bike. DAHIK!!!
To locate a vacuum leak, use an unlit propane torch and let the propane flow around the carb boots and vacuum lines and listen for an rpm increase, if something should set off the propane just pull the torch away and turn it off, the average small utility torch does not put out enough gas to cause more than a small "puff" of flame should the vapors ignite and that will be gone in a millisecond before it can do any damage.
A couple of years ago we got to watch a young man check for leaks on a very nice looking Harley, he was spraying WD-40 around his carb and it caught fire, within seconds it had melted a gas line and it was all over for the bike, and the pickup truck the bike was in.

[ScottsXS]

its actually like the butterflies are swelling when they get warm, as you can stick a finger between the carbs and push the butterflies closed, and the idles comes down as they close more. but it only does it @ operating temp thats the only prob it has checked for vac leaks...none. and fully synced

[psycoreefer]

Sounds like a linkage problem maybe. When was the last time the throttle cable was lubed? Are you sure the throttle is returning all the way? Maybe a weak spring on the return or something? If you can close the throttle with your fingers and fix the problem then I think you should start looking for something that is sticky. Not sure why it would only happen hot.

[DiverRay]

This may sound rude, but try your sync, starting from "0"! Un-adjust all the sync screws on the carbs , and then go back and start over. The carbs I just rebuilt had that problem when I first put the bodies back together. Once I went through and had the bench sync close, it seemed to help a LOT.
Just my $0.02

[81xsproject]

I had this problem from leaky float valves. The bike had no intake leak and was properly synced. It is just like the high idle the choke gives you after it is warmed up. I replaced the valves and reset the float heights. Problem solved.

[ScottsXS]

diverray, input is never considered rude and no offense taken i will try resyncing from "0" and 81xs iwll also check and and replace float valve and re adj float height thanx for the help