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Jethrro

Stupid jetting question

3 posts in this topic

I think I got the problem figured out but I wanted to make sure. 04 Wr 450 all the free mods and yz cam. When I crack the throttle (1/8 to 1/4) and hold it steady there is a lot of rpm fluxuation acompanied with some backfiring. Now when it comes to carbs I am mentally handicapped. But my best guess is that it is running lean and to fix the problem would be to go up in size on the pilot air jet or could I just turn the screw out. Do they both do the same thing but in a different way. Or am I way lost. I'm trying to save up enough corn to get the JD jet kit but I'm not quite there. Thanks

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The pilot screw adjusts the amount of fuel that goes through the pilot jet.

Think of it like this, a garden hose with an adjustable sprayer nozzle compared to a fire hose with an adjustable nozzle.

You can adjust the spray from the fire hose down to pretty close to that of the garden hose, but you can't get the same flow from the garden hose that you can from the bigger fire hose. Get it?

When you have adjusted the pilot screw out more than say 2-2.5 turns, it's recommended to go up one size on the jet, and then back the fuel screw in a few turns and start again coming back out to get the proper flow.

It sounds to me like you're lean as well. If you've never adjusted the fuel screw at all, it's probably about .5 turns out. Screw it back in until it seats (lightly) then back it out about 2 turns and see how it runs. Then fine tune it from there. :thumbsup:

Btw, you may want to look into a Zipty fuel screw. You can easily adjust the fuel screw when you have one. I adjust mine everytime I ride.

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