My son rides a 04 2.9 Sherco. On hot days in the summer, at trials events, after riding an hour or more, sometimes (randomly), if he turns it off, it won't restart. It seems nothing will get it restarted other than waiting about 15-20 min.

Is this common? Is there a fix?

Thanks mates!

Fuel in carb getting to hot ?

How can I tell if fuel is getting to hot? Now that you say, the last ride we went on, we had rode 6km home after riding trials. High gear, half-three quarter throttle the whole way, and his plastic heat guard on mufffler was melting, and seat plastic has two bubbles from the heat. Why did the exhaust get so hot? We've made this same scenario/ride many times. Separate issues?

Have you tried using the choke ?

Yes, choke didn't do it.

If the bike is going to be ridden at sustained high throttle openings consider richening the jetting until the plug is a darkish chocholate brown. What oil ratio are you using?

It could be the rings / bore are a bit worn and low on compression with quite a bit of blowby when really hot. This would make it hard to start.

Occasionally a faulty source or HT coil can cause poor starting when they get hot.

Don't know where you are located, what fuel you run, but insure fuel line is not up against the muffler, you might fit some heat pad between carb and muff as well.

There is supposed to be heat reflective material on underside of rear fender as well.

Long story made short, under certain conditions, high heat from exhaust may cause fuel vaporization in the float bowl or vaporlock. This may worsten using winter blend fuel in hot conditions, certain race gas or avgas blended for best atomization in cooler temps.