Have a 90 sportsman for my son. Runs great, but lately after 15 minutes or so & heat builds up it will stall. Seems starved for fuel. If I remove the fuel line from the top of the carb and let a little gas run out, it will start right back up and run 10-15 minutes and do it again. I drained the fuel bowl and cleaned the carb. Run new gas through it several times. Plug runs clean. Thought maybe a vapor lock but there seems to be no pressure build up in the tank when I remove the gas cap. Any ideas? Vent line clogged?

Thanks.

 

Couple of things you might check.

1. The safety teather on the rear of the atv. remove it and plug the wires together.
2. Leave the gas cap slightly open and give it a try.
3. There are two models of that engine. One uses a standard fuel shut off valve and the other uses a vac pulse shut off valve. If you have the vac, make sure the small vac hose is properly connected to the front of the Mikuni carb.
4. If you are running the stock NGK B7HPS plug, change to a B8HVX or B9HVX regardless of plug color. The B7HPS plug is a protruding electrode that was intended to help keep the plug clean on long service applications. It is a major cause of problems on the little atv's.
5. When you experience (it will happen) hard starting, unplug remove and clean the electric choke. Then reinstall it without connecting the electric wires. The electric choke is known to have problems.
6. If all of the above has not produced the desired results, note if the engine has lost power recently. If so, there is a 90% chance the head gasket is leaking. This problem will also cause the stall.
7. If you wash it down, water may get into the left hand controls. You may get a problem here. Open and inspect. Add di-electric grease for good measure.
8. If you still have problems, your CDI box (that little black box mounted up under the front fender) probably has an open circuit when it gets hot.