Sportsman 500 HELP!

[Yamahopper]

I Just picked up a 1999 500 Sportsman. It runs great until it gets to full warm and then it bogs down when you hit the gas over about 20 miles a hour. It has 95 HRS. 600 Miles, 4 stroke, Liguid cooled, Oil cooler with fan. Slight knock when hot. Where do i start looking on this machine? Help me Please!

[Neiko]

Just for the record I am not a gear head but I have had a 95 Explorer with 3800 miles and a 98 with 3700 miles on it so far and I do most of the maintainence myself on them.

The question I have for you is when the machine is cold does it go past 25 MPH? If it does I would take a look at replacing the air cleaner and spark plug with new ones.

If it never goes past 25 MPH from the start but the engine revs fine take a look at your primary clutch. You will have to take it apart and look at the 3 plastic mushrooms that have screws holding them in place. I had one break off in the clutch and the wheeler struggled to get to 30 MPH. They are cheap to replace and I think they must go out alot because I went to the dealer for 3 new ones and they only had 2 left but were getting 24 more the next day. It cost me less then $9 to fix were as if I had taken it in I am sure it would have been $300+.

Good Luck and let me know what was the culprit.

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Neiko

[Yamahopper]

It runs smooth and goes up past 45 no problem when cold. The guy said it has a new plug but i will look and make sure it is the right one. Air cleaner looks perfect with a blue sock over it, clean also. I am going to pull some plastic and check some hoses and wires.

[bae501]

I would start with the wires. Had problems with my 98 xplorer, when I put on the high beams it would bog down. There were 2 wires that had come disconnected.

[sledhead]

Check your valve clearance. Should be .006 thou on both the intake and exhaust valve. Sound like they could be tight. engines will lack in power as the motor gets hot with tight valve. It's a simple procedure. all you need is a 8mm wrench to remove the valve cover bolts a 10mm wrench to loosen the tappet adjuster and a very short flat tip screw driver to adjust them. a .006 thou feeler guage to measure the clearance. set the motot to top dead center. there should be to punch marks on the cam gear that indicated top dead. with play in the tappets. if no play rotate the motor 360 degrees with the pull rope and check for play again. adjust from there.

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ride safe, wear a helmut, stupid hurts

If you get'em serviced, wash'em first.

[Yamahopper]

A big thanks to all so far! Here is what a have found so far. The foam under the gas tank has broken up and some was pulled into the air box,may have been restricting the air flow. Two wires off, one for low beam lights up front and one for the high temp light on panel. Plug looks carband up for being new. Seems to rev-up beter with air cleaner off carb when hot now. I have a Hanyes manual coming and will look at valves next. Keep the tips comings hunting is here. Thank You All!