Does jetting change with a new piston and rings?

[Rcannon]

Bike is 1997 YZ 250. Piston is weisco pro-lite.

The old piston had quite a bit more wear than I believed I would find. It was ready!

I am at 4500ft of elevation . I was running a pilot one size smaller and a main two sizes smaller with the old top end.


I have not ridden the bike much. Just up and down the street to heat cycle the new piston. The plug now looks very dry and about the color of black coffee. Previoulsy the plug looked wet.

Thank You guys for all that you post. I searched top end rebuilds and had several hours of great reading. It is great how a post from a year ago can still help someone.

I am also shocked at how quiet this machine is. The old piston was shaking around a bit!

 

[Rcannon]

I should also mention I am using Yamalube R at 32:1. Conoco premium pump gas.

 

[125 rider]

This may be just in my head but i have always found my bikes run a bit richer after a new top end. Maybe because of the tight seal from the new piston & rings sucks in more gas? I usualy have to go down one step on the main and back out on the air screw a lot.

 

[Glitch]

I have had the same experience 125 rider. I bought my bike used and the cylinder was worn. So I had it bored and I had to go from a P2 piston to a P4. Anyway, I had to go down from a 160 to a 150 main. But for some reason I had to turn the air screw in. ::think