what could the problem be?

[YFZ450Ridr]

i just had my motor rebuilt with a new crank, piston, and cylinder. i rode it twice and now it doesnt run. the second time i rode it, right at the beginning of the day it just all at once bogged down and died.

im pretty sure that since everything from the cylinder and below is new that its nothing down there. that leaves me with the valves, carb, and plug for problems. i checked the carb and the floats were not stuck, jets not clogged and fuel comes into the bowl fine. i put a new plug in to be safe and it works just fine. i checked the valves and the exhaust are a tiny bit tight along with the middle intake valve.

can the valves just tighten up like that all at once and cause it to not run? it acts like its not getting fuel into the motor when you try to start it. im going to adjust the valves back to spec anyhow, but i just didnt think valves could get so tight all at once, after 10 hours of break in riding. any ideas guys.

[honda300EXtreme]

i think its the valves, especialy since one of the intake valves is tight, and on a recently rebuilt engine the valves can tighten up pretty quick,


and you are getting spark correct?

[YFZ450Ridr]

yep its got plenty of spark, i know this forsure because while testing for spark i shocked myself a good one

[250X_project]

Adjusting the valves is always good, but I would lean more towards the fuel. I'd make sure that the carb is taken apart, cleaned, and rebuilt.

Run a compression test to tell you if it is the valves or part of the new rebuild.

If they did a valve job on it, than the valves can tighten pretty quick when they seat themselves.

Check the plug to make sure you have fuel coming in. If you have fuel, test good on compression, and are still able to shock yourself :D Than you need to check your timing.

Good luck.;)