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roylo

Pilot Jet/Fuel Screw

3 posts in this topic

I have an after market muffler fitted to an otherwise standard 08 YZ450F. The bike seems to run very good. The jetting has been richened to a 168 main jet and needle 1 clip position richer from standard. Pilot jet is standard. Ive found the optimum setting of the fuel screw to be 2 1/2 turns out. Does this mean I should go 1 size bigger on the pilot jet and re-tune the fuel screw?

My main question is if I have the 45 size (standard) pilot jet fitted and tune the fuel screw to where it runs best as explained above, then fit a bigger (48) size pilot jet and re-tune the fuel screw will there be any difference to the overall tune of the engine?

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I'd leave it. If it has to be readjusted more than 2.5 turns then swap for the richer main

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I have an after market muffler fitted to an otherwise standard 08 YZ450F. The bike seems to run very good. The jetting has been richened to a 168 main jet and needle 1 clip position richer from standard. Pilot jet is standard. Ive found the optimum setting of the fuel screw to be 2 1/2 turns out. Does this mean I should go 1 size bigger on the pilot jet and re-tune the fuel screw?

My main question is if I have the 45 size (standard) pilot jet fitted and tune the fuel screw to where it runs best as explained above, then fit a bigger (48) size pilot jet and re-tune the fuel screw will there be any difference to the overall tune of the engine?

It depends on temperature for me and my bike. I run a 168 main, 45 pilot and the clip one richer. I had a 48 pilot in the bike and found that it ran fine but starting the bike when hot was much more difficult. Also, if you turn the fuel screw in with a 48 I found that you could screw it all the way in and the bike would not die, thus the jet was too big/rich. I'm not getting any popping with the 45, so it stays in for now.

I plan to run the 45 for the summer and this winter put the 48 back in when the air is bit more dense.

good luck

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