I have a 1999 Yamaha Grizzly 600. It starts right up but after about 10 minutes it just shuts off. Wait for a couple of minutes and it will start right up. Then about 5 minutes it shuts down again. The longer I let it cool down the longer it will run.

Thanks for your help

Bill Hudson

Bill,

This could be a combination of things ranging from electrical wiring, engine compression and stator or coil failures. The best way to figure out this kind of problem is to take one issue at a time. It’s a pain, but a necessary evil unless you just want to haul it off to the dealer. Start with the easiest and perform a compression test when the engine is cold and after running the Grizzly until it stalls test it immediately again. Compare the two results and if the second is significantly lower than the first you might have found your problem. Having a Yamaha Service manual to compare proper “In Spec” compression numbers is very important. If low or out of spec compression is found then you will need to service the top end of the engine.

The next step if Compression is good will be to look over all of the wiring harnesses that might come in contact with hot surfaces, such as exhaust or even the cylinder head. Make sure the wiring in these areas has not been melted or chaffed in any way.

The final test if all else proves to be in good working order would be to test the coil first and then the stator. Coils can become faulty due to extreme temperatures and age. As the engine heats up the coil looses its resistance and fails to deliver the charge needed to start the engine. Without bombarding you with technical numbers or making you buy testing equipment, I would simply run the ATV until it dies and pull the plug. Immediately before things have time to cool (yes, wear gloves), place the plug wire on the plug, hold the plug end, where the spark is, against the cylinder head and press the start button for a few seconds. If you get a nice blue spark then you have most likely eliminated or at least discounted the coil being faulty. This also lets you know that your stator is living.

The final suggestion that could be an issue is fuel. Is the machine getting the proper amount of fuel to the carb to run? If the fuel is just slowly running into the carb and is hindered by varnish or things unknown, then that would explain the run times and the fact that it runs longer after it cools down because the fuel has time to refill the float bowl. Fuel system cleaner such as Liquid Performances Ethanol Equalizer works wonders on shining up the interior of the carb.

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