I have a 2001 Zr600 EFI APV with about 4000 miles on the clock. Lately it has been acting up some. It works fine at most engines speeds, but if I am operating at a steady speed with the engine right around 7000rpm the engine starts to hunt (for lack of a better term) or surge slightly. She doesn't seem like its miss-firing but surging, almost like you were slightly modulating the accelerator. It starts great and pulls hard right up to about 8300-8400 rpm, and the plugs look good. I have noticed a slight stumble on acceleration sometimes, almost like it loses its gas for for a split second, otherwise it has always worked great. I was wondering if anyone has run across this problem before, or has an idea what might be causing it? Thanks in advance.