Hoping someone out there may be able to provide a little guidance. 86 xr250. Starts first kick, runs strong. Absolutely perfect intil engine get thoroughly warmed up. then the engine is VERY slow to return to idle speed. Cables have been lubed Throttle snaps back to stop, engine speed doesn't. Any ideas would be welcomed. It my sons bike, he's pretty much a newbie. Don't think I want him having to deal with a slow or stuck throttle. Thanks for teh help.