Pilot Jet/Fuel Screw

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?

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

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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