‘07 CRF250R Hard starting after rebuild

[bubbaxr]

‘07 CRF250R Hard starting after rebuild

Complete head rebuild with new OEM components.
Shimmed to spec, spring heights look good, everything went together just fine.
The motor simply will not kick start.
So we get a tow strap and pull it down the road.
After some hesitation it fires up and seems good to go.
30 minutes break in and clearances are checked. OK
Next day (cold motor) again will not start so we tow it again. Another 30 minutes on the track.
Now it starts when hot. Check it after a wash (now cold) - starts again just fine.
I’m a little hesitant to pay a race fee until I understand what’s up.
Any thoughts???

 

[Ol'89r]

First, you should never tow your bike to start it. If is doesn't start within a few kicks after a rebuild start checking for something wrong. You probably only had it flooded but if you would have had a shim out of place or the cam timing off, you could have done damage by towing it.

Re-check your cam timing and disable the automatic decompression release and check your compression.

 

[_JOE_]

Take a look at the auto-decomp setup on the end of the cam. Quite a few folks are finding easier starting by grinding the hump shorter on the decomp rod. Have you tried richening the fuel screw?

 

[bwood]

My guess would be that the cam timing is a tooth off. On mine, when the arrows on the cam gear are parallel with the head, the dot on the crank gear is slightly above the arrow on the case. Also make sure the weight for the decomp system will swing freely when the rpms get up and springs back on its own sitting still. And double check the valve clearances one more time.

Exhaust .011" +/- .001" (.28mm +/- .03mm)
Intake .005" +/- .001" (.12mm +/- .03mm)