I have a 96 Arctic Cat Panther with a fan cooled 440 Suzuki. Good compression, good blue spark, went thru carbs, new plugs. One cylinder coughs/backfires through carb. Switched carbs around and it stays with the cylinder. Sprayed carb cleaner all around and doesn’t rev up. No reeds it’s port injection. Bore scoped and piston skirt looks good on intake and exhaust side. Can figure this one out fellers.

Sounds electrical in nature. I’d first look at plug wire. And then change the plugs, they sometimes will look okay when checked for spark but then not keep up with the engine running. Always start with the most simple! Good luck

Ohhh, you have new plugs…

Yeah it does sound electrical. Maybe a bad coil or plug wire or bad black box

Sorry should have mentioned tried new coil and wires and Cdi box, nice blue spark, jumps over a 1/4”

Just figured it out, crank is out of phase, way out. Puzzles me because never blew a belt, something must have ran through the combustion chamber. Thanks for the replys.

Now that you have it running good, wanna sell me the motor lol.

Steven, I don’t have it running yet, just tearing it down. Don't want to sink too much in the old girl.