jetting my bike

[howard113]

now, I know no one can really confirm if this will be a good set up,jettting is more trial and error. but does this sound lean? bike is an 03 yz250f. i currently live in upper NY and in 2 months im moving back to southern-california. During the summer out there,it gets hot! dry heat,everyday during summer its about 75+ degrees so i figured i would swap out the stock 40 pilot jet for a 35 and then swap out the stock 178 main jet for a 165. Or does this sound like it would be too lean? If this setup doesnt sound right,what do you suggest? I plan on buying new jets within a week or so and doing the carb up asap.

i know bikes run richer in the summer which means run smaller jets and this is why i plan to do this. If this changes anything,only mod to the bike is a full Dr.d pipe but the DRD website calls for stock jetting with the pipe.

thanks guys:thumbsup:

[William1]

Makes no sense. You are going to swap out jets based on a pure guess?

Chances are, your pilot will not change at all, just a little change with the fuel screw

Might have to move the needle a clip, might have to change a size in main.

But this all MIGHT HAVE, not have to. Wait till you get therre, ride and test.

Jetting is about air density. That is a factor or Temp, Air pressure and Humidity. You have these three values, you can plug that and your current (I assume) perfect jetting in to a formula and it will spit out close to perfect jetting at the new air density.

Jetting for Altitude and Weather

But wait till you get there and test ride.

Stock YZ pipe is open, you put on an open aftermarket, no surprize the jetting did not change.