Linhai xl 260
 

Quad starts missing when hot. Any suggestions?

Try a new plug. Also take a look at the old one. If the nose is black and sooty either the choke is sticking or air filter blocked, or possibly an electrical fault. If the plug nose is white, including metal part, a weak mixture, probably due to a partly blocked jet.

black and wet
 

what if its black and wet ?

Same as black and sooty.

black and wet
 

https://cimg8.ibsrv.net/gimg/atvconn...c9b2c207fc.jpg
black and wet

Tip isn't black, so mixture is about right. Seems like the spark is disappearing when hot. Can be any of the electronics, plug, coil regulator, CDI or stator. With intermittent faults substitution of components, one at a time is about all you can do. Regulators can be checked, put a voltmeter across the battery with the engine running, rev up, if it goes over 14.5v the regulator is overcharging.