'06 yz450f miss / backfire

Ok, help me out guys. I have a completely stock '06 yz450f that has a bad miss with backfire at about 1/4 throttle. I have cleaned the carb, thinking it had a dirty slow jet but still it's doing it. Is it possible that a burnt valve is the cause? Is the timing off?

Did it use to run well? What's changed?

Could be a bad TPS. Try it with the TPS unplugged once.

is it cold out?? could be lean

have you had the bike apart any??..if so it could be out one degree or half a degree.

The weather has been on the cool side but the spark plug doesn't indicate being lean. I did check the valve clearances but I've never had the motor apart.

I bought the bike 2 months ago and I've heard that it isn't odd to hear them pop and crack some. It didn't concern me until I was practicing starts and it was very noticeable missing with fire coming out of the silencer.

I'll try the unpluging of the TPS. Then I'll be back tommorrow with results and more questions. Thanks alot fellers!

unplugging the TPS didn't work. Is it possible that the hot start could cause this? A guy from work ask if I checked that. Thanks for the help guys.

The hot start could do that, yes.

unplugging the TPS didn't work. Is it possible that the hot start could cause this? A guy from work ask if I checked that. Thanks for the help guys.

Where do you have the fuel screw set?

Here are 3 things that are suspect:

Fuel Screw - buy a adjustable fuel screw to set this correctly -probably is not set correctly - ZipTy has these

Hot Start plunger - may be sticking in carb, moisture comes in from plastic nut on carb replace with Alum nut from ZipTy

Jetting is off - Also I suggest replacing the stock needle with newer NFLR you can get from any dealer.

I had a similiar problem and tried all the usual stuff. Cleaned the carb etc. I have another 06 so I started swapping parts. I would never have guessed it but the black box was the problem.

i was told by some guys at my local shop that the 06's had issues with backfiring/popping due to jetting. it was happening with mine on decel. i changed the slow speed jet and it went away.

My '06 did the same as well as all kinds of backfiring upon chopped throttle compression braking and starting issues when hot - right off the bat. Had to take it back and they rejetted. Smooth as a babys bottom end ever since..

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