It a air cool and it dies after it gets hot then crank back up. I done change the fuel lines cid box and the exciting coil and the coil.

 

Check compression..

 

I done put new rings in it and that has not help.

 

Rings alone on a worn out piston and cylinder usually doesn't help,at least not for long. You're talking about thousandths of an inch clearances and if the piston to cylinder clearance is already too much,just sticking in new stock rings wont help. Just do a compression check to see where you stand. If it's at least 115 psi,preferably more than that,then move on to carb,fuel problems,air leaks or a possible electrical breakdown.

 

I checked the compression and it's got 125. I blown all the vacuum lines out and and it die once.it cranked right back up and I rode it hard for about 20 minutes and had no problem with it. I had the side panels off of it when I was ridding it. Could it be its not getting enough of air to keep it cool with the side panels on?

 

Easy enough to check if the air box inlet is blocked. If you still have the foam collar,make sure that it isn't blocking the air inlet.Dirt Cheap Yamaha, Honda & Polaris OEM Parts & Accessories – Cycle Parts Warehouse Plus pull the fuel line off and check that you have good flow from the fuel valve plus make sure the carb vent line and tank vent are open. Remove the fuel cap if you wish and test it out. Running hot normally wasn't a problem on the 300. Basically an air cooled engine with a fan that rarely kicks on unless super hot because the sensor is mounted on the top motor mount bracket and not on the engine itself.