05 wr 450 backfiring on deceleration?

Hey guys, whats up with this thing backfiring on deceleration?

I have done all of the "free mods"

gray wire

throttle stop


Is this normal, or how can I fix it.


Remove the AIS. That will help to get rid of the lean condition in the exhaust that is causing the backfire. TT store has a good plug kit for sealing up the holes once the parts are removed.

thanks moto jason

what does the ais actually do?

and does it rob power ?

AIS Air Injection System aka smog pump. Yamaha added it for 05 450 to get it green stickered.

does not rob power. once i removed mine, no more popping. i think the ais removal kit is a must have!!

Removing the AIS alone may not be enough. You will probably want to rejet to get it just right.

For an '05, backfiring on deceleration is usually caused by one or a combination of the following:

  • AIS
  • Lean needle position
  • Lean fuel screw adjustment
  • Lean pilot circuit
  • Loose connections in the exhaust system

Check and adjust each of these individually and you'll figure it out...SC

Is that just for the California bikes purchased in that state? I bought mine in Oregon. Do you have a photo odf the AIS procedure?

I'm at 5280' and mine still popped after AIS removal till I rejetted. I'm running a 50 pilot which is a bit rich (waiting for a 48) I raised the needle by inserting a .020" washer under the needle clip. You have to pop the aluminum plug outa the float bowl side to get access to the fuel screw which I'm running at 2-2 1/2 turns out.

what about the yz 450? ( 05 ) mine too has a little popping on decel. dealer told me normal... but id sure like to get rid of it

I'm not so sure I'd blame it on the AIS.. I would say there's a 90% chance your Pilot jet is too lean... All these "Free mods" will do very little without proper jetting specs... Go to the Jetting Database and see what we're all runnin... :)

Dan is right about it not being all related to the AIS. I meant do the AIS removal and then re-jet. I've got a JD kit and am using the settings recommended in the Jetting Database. Now my bike runs great!

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