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Discussion Starter #1
guys, I am new to the forum and thought I would try to explain what was happening to my 08 sportsman 500 H.O. to see if anyone has had this happen or might know what is causing the problem. I bought the machine new and for the most part, it runs great. However, during the summer months when it is hot, after a long ride it will start to backfire, sputter or miss, and when you let off of the throttle it will go dead. It will not start again until it has completely cooled off. The fan is working fine, no warning lights or anything. Any help would be appreciated. Thanks!
 

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sounds like you may be getting vapor lock....you can try to insulate lines and the bottom of the tank some more...there is a thread here on that an what was done to fix it....try search for vapor lock....
 

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I would check a the vent lines and make sure you have no blockages. You can get some vapor lock issues. Kind of hard to try now but when it does it try taking the gas cap off to release any pressure.
 

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Discussion Starter #4
I will search that and check it out. Only does it in the summer when it is very humid outside. In the winter it runs great all day everyday. Thanks for the info. Maybe I can get the problem corrected so I am not gun shy about going on long rides in the summer. lol Thanks!
 

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if the vent lines were blocked it would happen in any weather....it sorta creates a vaccum so the gas wont flow..
 

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Discussion Starter #6
I have read some of the posts on vapor lock. Sounds simular to what I am experiencing except most people seem to get their machine to start after a few minutes of cooling. Mine wont start again until it has completely cooled off. (Block is cool to the touch) Which is several hours
 

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get some of the sticky sheets of insulation....and do the bottom of the tank also....I think napa sells it...or any speed shop....

this is the stuff....

try auto parts stores.....
 

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Discussion Starter #9
thanks guys for the advice. I will go to napa tomorrow and see if they have any and put it on the machine. I also have a problem with the digital fuel gauge which shows that it is almost empty when it is actually full. It also blinks alot. Any thoughts on what is causing that??
 

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I went through all this too ast summer with my 08 500 ho. New pump, lined tank, metal heat shield for the tank, still had issues.

Funny you mention humidity because my problem that I thought was heat, was really moisture. My spark plug boot had a hole in it and while dry it ran decent enough, but if I got any moisture on it it would ark out to the head and die. Some rotunda rubber tape and a layer of vinyl super 88 and it hasn't ran better! Just takes a pin hole to cause a short. Pull off the side cover while idling at night and look for some extra sparking.
 

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A friend of mine had a similar issue on his 08 500 Sportsman a couple years ago. He spent countless time and $$ chasing the issue. It ended up being his stator had some type of short in it, that the heat/humidity made worse.
 

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Discussion Starter #14
Yes, it is very frustrating not knowing what the problem is. It seems like it only does this in hot weather from june until september. When the weather is cool or cold, it runs great. I'll try the insulation and check the plug wire and see if it helps.
 
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