I have a 1990 Yamaha YZ 250 WR, the bike is in really nice condition, but I'm have some problems with it. I'll start the bike up and ride it and it runs fine, but when I let off the throttle, the motor will sometimes rev up and seems like the idle is set too high, however the idle screw is not even touching the slide and the slide is completely seated to the bottom of the carb when the throttle is closed (that's another problem, if I use the idle screw, the bike idles way to high). I have all of the factory jets and the air screw set at 1 3/4 out (stock setting, this is where the bike is most responsive). The bike has Boyesen dual stage reeds, a FMF Fatty pipe, and a new Answer Racing silencer (is it possible to mismatch a silencer to a pipe). When the bike revs up, it reminds me of what a bike will do when the gas is shut off and the rest of the gas is being used up, the way it cycles up and down. I checked the carb and cleaned it, replaced the jets, and looked at the fuel inlet valve, which appears to be in good condition. The floats don't seem to stick or anything. I also checked the intake area and the base of the cylinder for air leaks, I did this with a propane torch that wasn't lit (is this a good way of checking). The bike runs really smooth and has a ton of power and only does this when I let off the throttle. If anyone can assist me in troubleshooting this issue I'd appreciate it.
