WR450 back fire

I have a 2006 WR450, with an AIS kit and the Power Now kit, which includes the power bomb header, FMF Q2 series pipe and the Power Now insert on intake side of carb.

I change the pilot jet to a 48 and the main jet to 170. The AIS kit came with adjustable needle set at 3 notches from the top. It seems to back fires when I backed out of the throttle. (I was riding in the Mojave dessert, California.)

The Power Now's instructions talk about "a fuel adjustment screw," I have the stock carb, but I cannot see, nor find, the fuel adjustment screw. :crazy:

Any suggestion on where to look for the adjustment screw? Or why it back fires?


Fuel screw is covered with a washer that you should take out anyway.

You need to take float bowl off and then just push it out with punch.

Fuel screw can be found on the cylinder side from the middle (sideway) from the float bowl.

Timo Mc

Have a read through this tutorial by one of the TT members - comes from the jetting forum.


Jetting the Flat FCR carb, DIY picture tutorial.

About half way down is a good pic of the under side of the carb with a red Zip-Ty fuel screw in the place where the original is sealed under an alloy plug.

After you get a replacement screw, punch or pull the alloy plug out (i suggest you remove the float bowl or take the carb off to do this) and be VERY careful not to lose the spring, small washer and O-ring from the original brass screw. Put these on the replacement fuel screw- spring,washer then O-ring and carefully insert and wind in. Count the threads first so you know how far to wind it in until it LIGHTLY seats, then back it out around 1.5 turns...and then visit the "how to tune your pilot circuit sticky", by BURNED.

Have fun :crazy:

BTW, this is just the start of your jetting!!

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