I need help in on my sons 2008 crf 450r it runs good when its running but what the problem is when he runs it hard you better get ready when you get it back to the pit area and put a new spark plug in it. The thing about it if you keep the spark plug in it and not put a new one in it it won't start,but as soon as you put a new spark plug in it the 1st or 2nd kick it will start right up.Sometimes the old spark plug will be wet and sometimes it will be dry don't under stand it. Valves are good and the motor on a complete rebuild has only 10hrs on it if someone could help me out you can call the shop at 903-581-1717 ask for Ricky or cell 903-707-6930 or jay 903-283-4105 thanks......

Sounds to me like the float is sticking. Or possibly the check valve in the AP is leaking and its drawing fuel from there too.

Id just give the carb a good douche, spend some time dialing in the fuel screw and verify the float isn't hanging up.

Probably wouldnt hurt to check the valve lash either. It may be hot enough to zero the intake lash and by the time you get a new plug in it, its cool enough to fire again.

When it didnt want to start, have you ever tried to bump start it? If it fires right up, its probably the intake valve lash at zero (or less!)

That bike shouldn't ever foul a plug if the jetting is correct. What is current jetting? Elev.? Fuel type? High comp. Piston? Is oil sucking into the carb through the crankcase vent tube?

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