xr500 missfire

[lb99]

I have an 81 xr500 that is missfiring badly at anything over 1/4 throttle, it starts and idles fine and has plenty of torque, but just misses when you try to open it up, any suggestions?

I might add that the motor is in a klr600 frame, and while the engine mounts seem to be properly made, heaps of other stuff is bodged up, including the wiring

[tri boy]

An Xr engine in a KLR frame.
Oh the humanity.

Next they will be breeding tigers with garden snails.
Can't help you with the fault. Just methodically work your way through it.

[lb99]

lol, it did seem to be an odd choice for a conversion, but you know how it goes when you have an old frame laying about...... the dude who owns it is in love with it though, and has spent many thousands on it, but it still doesn't go properly.

[kiwi cowboy]

I have an 81 xr500 that is missfiring badly at anything over 1/4 throttle, it starts and idles fine and has plenty of torque, but just misses when you try to open it up, any suggestions?

I might add that the motor is in a klr600 frame, and while the engine mounts seem to be properly made, heaps of other stuff is bodged up, including the wiring

Is it missing or more of a crackel missfire?.

Possible its running lean when running on anything but the idle jet.

Is the airbox standard or modified and what size main jets are you running?.

Check for leaks between the airbox and carbs.