hey i have a '00 zx9r....in neutral it revs up good but backfires when you let of the gas....in gear it runs eratic with no power ....changed feul pump same thing....it ran pro and i parked it for about 2 weeks then it started this issue when i started it after it being parked...Thanks

 

Mine is running rough, but not quite as bad as yours sounds...

Did you get itt sorted out? sounds like it electrical to me, but I'm not that clever on bike faults, thats why I joined here lol!

Mine idles slightly uneven and it magnifies when I'm riding esspecially on over-run it jerks the bike back and forward like an knackered old chain slaps when rear wheel is off the ground and engine is driving the wheel......any ideas?
Could just carb balance be the problem, or wrong jets for the Can, ignition timing, fuel/air mix ????? Help!!!

 

VERY often on (at least) the early 9's, rough running (that bucking bronco thing) can be traced back to bad gas. I've said this before; 9's were really well vented, which means the gas loses fizz over a few weeks, especially in warmer climes. Start simple and cheap when troubleshooting and go progressively more involved. See what your plugs tell you; what does deposit look like? Clean, replace fuel filter. Get an inline one if you don't have one; they're cheap insurance. Drain the carb bowls and get fresh juice in there. Then, look at the jets. The smallest crud can block flow. Check the primaries or secondaries (mains) depending on where in the revs you get bucking. If the fuel is bad, the gas and exhaust may smell peculiar. Check for spark. Pull each plug and fire with the cable on, and electrode grounded to the engine. Good spark on all 4? Check for shorts and a good ground through the bike. By doing these relatively simple checks, you've eliminated variables which can be hidden when you begin to replace parts. If you replace the exhaust can, you (9/10 times) will need to re-jet. However, THAT is a different engine response than bucking (like bad gas) and your plug deposit will tell you all you need to know.
If I can help, let me know. I have an old 9, too.