300ex running like sh*t

[etondaddy]

OK two weeks ago I put a new sleeve and knocked the hole to 76mm and put a stage one hot can in my boys stock motor and the the thing flew he had a blast. This past week practice and first moto was the same. Then it wouldn't start for the second moto......pulled it with a quad and got it to start but it ran like sh*t. He finished the moto. Checked comp. and only had 30psi....... OK it's blowed up right....?? got it home checked it with two more gauges and got the same thing. Took it apart last night and found nothing.....valves all look good and seated.... cyl. looks like the day I put it in ring gap is .004 and.009 bigger that the Wiesco spec....no big deal. When I took it apart the cam chain was right were I put it. No clue........ now when I took apart the intake valves were tight with the cam loops down...... that gave me a hard start before but after I got it started it ran ok....this time it's running bad.



Mike Kozura

[born2ride14]

my guess is valve adjustments, timing, good chance its the timing.

[shaungray89]

probable timing or you bent a valve when puting the head back on

[racer28]

id mess with the timing. when i had shears 250x i rode it a few teeth out of time and sold it just to find it was a raped ape when it was actually in time.

[sm00th026]

Did you retorque the head bolts and nuts after you ran it for awhile maybe you are losing compression through the head gasket or the compression oring on the bottom of your jug

[etondaddy]

I think I found it......the intake valves are dished out the surface that seats is gone. I got new valves coming this week. And you dcan see were they weren't seating. I guess that's why I kept getting tight.



Mike Kozura

[Tommy Warren]

was it blowing black smoke when it was running like crap? mine is doing the same thing but its all stock. it was totally lacking power and the intake valves were about .002 so I adjusted them to .004 which is the stock lash. now it won't run at all.

[etondaddy]

Originally posted by Tommy Warren
was it blowing black smoke when it was running like crap? mine is doing the same thing but its all stock. it was totally lacking power and the intake valves were about .002 so I adjusted them to .004 which is the stock lash. now it won't run at all.

I didn't see any black smoke....but he was out on the track. The plug was nasty black. The motor is basically stock and I always had a problem with the intake valve lash going to zero....I guess they were wearing into the head. Try the valve lash at 6 and 8 and see if it starts...if not pull the head off and remove the intake valves and check them. I'll post a pic of the bad valves tomorrow. If the valves come in tomorrow I hope to have it done this weekend. Take comp. and see what you got. I only had 30psi.


Mike Kozura

[Tommy Warren]

K thanks but the only thing is.....the bike ran at.000 lash now it ran for three minutes bogging like crazy and blowing black smoke. then it died and won't restart. do you think my timing chain slip a tooth?