I have an 02 500 4X4 auto which sputters and runs rough after about 20-30 minutes of continuous use. The fan and radiator are working okay and it doesn't appear to be overheating. After shutting off for about five minutes, it will run okay for about another 10 or so and the same thing happens. When first started, it runs great up though I still need to adjust the air screw to smooth it out at higher speeds (30+). I put a new thermostat in it with no effect. I have replaced the coil, spark plug and CDI unit about 50 miles ago and have rebuilt the carb as well. Any suggestions are greatly appreciated.

Also, I read on another post about a master cylinder rebuild kit. Are these available at dealers or do they need to be ordered from an online store?

Thanks for any help.

 

that kind of sounds like you are getting a vapor lock, maybe check your routing of the fuel line

 

Make sure the tank vent and vent hose are clear. To check if you want. Run with the gas cap loose and se if it happens. If good, it's the vent in the tank or the hose plugged.

 

You could have some trash in your tank, or some water in there it only takes a few grain's of dirt, sand or drop of water to cause this problem. It's worth a look your fuel at the gas station pump's can get dirt and water in the tank. Also the fuel line from the quad's gas tank to carb could be breaking down from the inside if it's the old rubber line. When you start it cold and warm's up it might run fine untill you start moving the fuel sloshing around stir's up any dirt,water in the tank. And put a inline fuel filter between the tank and carb when you put on new fuel line, you can get the new tygon fuel line and clear inline fuel filter from any small engine repair shop for less than your quad dealer ! Sorry to make long reply, just want to give you my thought's, i've had this kind of fuel issue's in my small engine shop on lawnmower's and my ATV's.................williebee

 

Thanks for the suggestions. I replaced the rubber fuel supply line with the tygon type and added a fuel filter a couple of months ago. I didn't change the routing at all but did notice where the feed is on the carb is close to the exhaust pipe routing to the rear. The line and filter definitely helped the idle and performance overall. I cleared the vent line and vent nipple on the fuel tank. They did not seem to be clogged but they aren't now for sure. My son says I over-tighten everything and the gas cap was no exception. I loosened it and just snugged it down resisting every last thought it my mind telling me to turn it tighter. I rode about 20 or so minutes last night and it did good though it was only about 75 degrees when I was riding it (compared to about 95 degrees when it had the problem). It felt like the engine was just starting to heat up good as I began to feel the heat on my leg. I will be riding this weekend a lot longer for a better test.

 

I forgot to note the fuel select valve on the gas tank does not work in the run (down) position. I have it set at the reserve (up) position. I am thinking the reserve position is to ensure you have at least a little gas left in the tank to get back to where you came from without having to push.

 

Other way around. In the "on" position there is gas left in the tank when the motor stops that the "reserve" position accesses. If you are plugged in the on position, you need to pull the tank and and clean it and that valve before you try anything else. You didn't mention checking and clearing the fuel vent. FYI the air screw is an idle adjustment and has very little to do with high speed running of the engine. Generally if the air screw is wrong idle will be very bad and high speed will still be fine.