I have a 2001 raptor 660 an can't figure out why it's backfiring when I go past 1/4 to 1/2 throttle I've read on the Internet an said it could be air to fuel mixture or needs bigger jets any info would help thanks

 

My son's Raptor was doing that. We found the wires under the shifter that go to the reverse switch had rubbed thru and shorted. The quad thought it was in reverse and kicked in the rev limiter.

 

The only reason I would change jets is for elevation changes and or engine mods. You shouldn't all of a sudden need a jet change if it was running fine.
Being 10+ years old I would take the carbs off and clean them, is your gas old? how does the spark plug look? should be light brown. I know the dual carbs can be a bit intimidating but you may need to dig into them to find the issue. Let us know.

 

Well over my weekend from work i took the carbs off a checked the jet cause i bought the bike of a guy an one jet size was 165 an the other was 155 so i replaced with stock cause sparkplug was black i got a new plug an the back firing is not as bad but still does it.. in first gear it spits an sputters after 1/2 throttle an second it wont hardly run.

 

I drained gasan put new in it

 

Is the needle clip in or near the middle slot? they both should have been the same, when you changed the jet did you check this?

 

If it still does not run right you can warm up the engine, turn up your idle a bit to a fast idle setting, adjust your fuel mixture down (clockwise turns at bottom of carb) so the engine speed starts to die down then back the screw out to get an optimum running engine speed...that point should be your setting to optimum mixture (just don't turn it fast)... then simply turn down your idle setting after that.

 

Yes both needle clips are in the middle slot an ok ill try that an get back to yall thanks..