04 Yz450f Carb Help Please

i recently rode my dirt bike for the first time after the winter and had no problems. i accidently put bad gas in it and it started sputtering and stalling so i soon realized the problem and drained the gas and then the plug fouled. i replaced the spark plug and it ran fine. i bought an aftermarket exhaust system and the power now system. so today i changed the motor oil cause it needed it and put the after market mods on. if you're not familiar with the power now system, its a carburator mod that streamlines the air for increased air flow through the carb. so putting those two mods on in one day i was somewhat expecting to rejet the carb to make it richer, but after putting them on i only adjusted the "idle nob" i think its called, its under the fuel on/off switch, anyway the bike seems to run fine to me but when the bike backfires it has a tiny burst of flame out the tailpipe. also when i shut the bike down and only when i do that the tailpipe smokes. does anyone think i need to adust the carb needle or is the idle nob good enough.

I wouldn't worry about changing the jetting the Power Now device shouldn't require any changes to my knowledge...The smoke from the pipe is most likely the bad fuel residue left in the muffler and will go away...The fuel needle on these bikes is pretty sensitive and can make a big difference when adjusted correctly...read your manual

well i swapped out the fuel and then put the aftermarket exhaust on so the new exhaust didn't have any bad fuel in it

If you only ran the bike for a short period could it just be the "new" burning off the inside of the pipe?? There may be some sort of storage oil or what ever in there that needs some time to burn out first. I think I read on here that some back firing is normal for a well tuned YZf.

ya thats what i thought too, i guess thats all it is. i'll check the spark plug and see if its running clean

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