mind of its own idle

[pugh]

thanks for your time! i have a 1980 Suzuki GS450L , the idle has a mind of its own. the problem is that the bike will be warmed up and idle fine for awhile. i can even start to ride but then suddenly at a stop light or just sitting in the driveway the idle shoots up and the tach runs up to 3000 RPM or more. yes the choke is shut off and i have relaxed the tention on the throttle cable to be sure throttle is closing all the way, as suggested i have let the bike warm up for 10 minutes and used the idle adjustment knob to get the idle where it should be...like i said , it will be just fine then out of no-where its shoots up ..i can rev the engine (even higher RPMS) a few times and bring the idle back down but it will shoot up again. when this excessive idle happens, even turning the idle adjustment to lower it has no effect.
also i have turned the front end back and forth to see if the movement of the throttle cable was causing it and that had no effect. ..just picture you're letting your ride warm up as you throw on your helmet and sunglasses as you walk towards your bike the engine just starts racing as if the ghost of a fallen rider is twisting his wrist on your cycle!

thank you everyone @ total motorcycle

[kar_the_terrible]

i had a similar problem while working on my yam xs400. i didnt touch the bike and it revved up on its own. At thetime i had my choke on, and it looked like it was running out of fuel, Buzz at the time suggested that this is due to a lean mixture. i have read in manuals that lean mixtures cause the engine to run at a higher temperature, which could be a cause for that to happen.
In some cases advanced timing could lead to the same effect (refer to http://www.dansmc.com).

[sparky]

I had the same problem on my bike, and found that the float levels were too high. Problem went away after they were adjusted to the proper levels. Don't know if this was the problem, but it hasn't happened since.