yamaha 80 four wheeler
 

? have a 1985 yamaha moto 80 four wheeler ,runs great when cold after 10 minutes rideing engine starts to run ruff , deadspots when accelerating ,what has been checked already, ,engineing timing ,new carb, float and jet adjustments to manual ,air screw 1 1/2 turn out ,fresh fuel,new plug ,new coil ,cdi for resistance,compression (new piston ,rings ) new valves lapped in and set to gap ,new cam chain , any thoughts

Have you checked the stator?