need help, stiff valvetrain

I need help on a 2001 YZ 250F. Its a friends and Im trying to help make it easier to start. I usually work on red bikes...:smirk: The bike is really hard to start cold. I put a new piston (wiesco). The valves are in good shape and adjusted properely. I completely went through the carb. Fresh gas, timing perfect.It seems like the bike is hard to get kicked through the stroke. We have been finding compression, burping the relief and kicking....When I had the valve train out I checked for rstrictions in the bore and its free but when I torque down the cam holders the cam become slightly stiff to rotation. I am feeling that this is being amplified by the gearing of the cam chain and making it hard to kick over. Any other ideas?

a new piston and rings should be harder to kickover than wornout.

especially if you put in a higher compression piston (but you did not say you did nor didnt).

the 01s were not easy to kick. i had 1 for 5 years.

the hard to start issue is probably because of jetting. what is yours?

Thanks for the reply. I know its really hard to kick....The piston is a regular weisco. Jetting is 175 main and 42 pilot. The needle clip is in the 3rd ring. The needle may be stock. Air screw was and is 2 full turns out. Kinda weird is I found 2 o rings on the air screw... It went o ring, o ring flat washer then spring. When I put the carb back together I only put one in. The other weird thing I noticed is the choke and hot start are reversed from my Honda...


there is no air screw on a 4strk.

set the fuel screw at 1.75 turns from lightly seated.

i would suggest you go 1 size lower on the PJ to a 40 and 2 sizes smaller on the MJ to a 170. this is good for all temps above freezing.

Fuel screw, air screw, same thing, only different!:smirk: No really thanks for the input. I'll try it.


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