I had an 87 that I restored and just had major issues with the carb. My bike ran fat on fuel at the 1/4-3/3 range area. I was able to find main jets and pilots but never could find the needle jet which in the VM38 Mikuni cab is the nozzle that the jet needle moves in and out with the slide. My bike ran very strong but you could tell it was fat in the middle. I ran 14/49 gearing and it was perfect for trails and fire roads. To help jet the bike right I would locate a newer kx500 carb/cable/throttle assembly off of ebay. That way you can buy the jets that are needed to tune the bike.