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Discussion Starter #1
hey all, this is a long story
i am helping out a buddy with his quad.
its a 97 sportsman 500.
he overheated it multiple times and could not determine what was causing it to overheat so he gave up and he put it away to sit for 4 months.
he asked me for some help and now i have a mess on my hands.
I was able to get it running with the fuel that was in it. problem was, once you gave it some gas it would sputter and backfire out the exhaust. I was able to get it to run long enough to get the temp light to come on. i determined the fan was not working (stuck) i freed it up and it seems to work fine now.
I rebuilt/cleaned the carb. drained the old fuel and filled with fresh fuel.
started it up and it started nice and easy seemed to idle pretty good. it ran for a few minutes and seemed good and strong. drove it around the yard 2 times. i pulled back into the shed to check out the water temp and the fan. As the machine got hotter it seemed to run worse untill eventually i could not keep it running and it died. i tried to start it hot and it would not start.
I pulled the plug and it was clean (no aluminum) with a nice light brown color to it. i grabbed my compression tester and checked the compression. i had like 25-30 lbs i knew something was wrong. Then then i saw the decompression hole in the cylinder and realised i was not going to be able to do a compression test.
the next day i was able to start the quad with no issues. i ran it for 30 seconds and shut it.
I am afraid he damaged the motor when he overheated it multiple times. Does any one have any experience with something like this? i have ordered a leak down tester to do some further testing but it wont be here for a week or so.
just hoping to pick a few brains and see what people thing might be wrong.
Any help is appreciated
thanks, Steven
 

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you probably won't be able to use the leak down tester for the same reason you can't use the compression gauge, I think there is a way to dis-able the compression release but I'm not sure how, also, there was a post on here somewhere about the fuel getting hot as the machine did and causing "vapor lock", it may be the same issue your having.
 

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Discussion Starter #3
i was under the assumption that when you use the leakdown tester you have the engine in top dead center so the decompression hole is actually below the rings. as i said just an assumption.
regardless i wanted one for a while now so this was the excuse to buy one.

you know i actually thought about vapor lock because i had very little gas in the tank (about 1/2 gallon) maybe i should put some sort of insulation between the engine and the tank and try it again.
the issue im having is IF there is damage i don't want to do more damage.
 

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usually one of the signs of damage is metal on the spark plug, with roller bearings in the wrist pin and crank shaft the affects of heat are less on those parts, usually the parts that get the punishment are the piston and cylinder, without metal on the plug it may not have bad enough to hurt it much. I'm not sure about the compression release, the trick to a leak down test it too hold the crank at TDC when you put the air in the cylinder. don't get your hands in the way of the clutch or flywheel.
 

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Discussion Starter #5
I dont think this is motor related. i am thinking it is fuel or carb related.
i started the quad tonight and ran it till it was hot.
It idles great while the engine is cold. i was bliping the throttle the whole time trying to warm it up quick.
once it was good and warmed up it would not idle. when it dropped down to idle range the motor would bog something awful when i was trying to give it gas to keep it running. once it was above idle range say 2000 rpm it ran strong and would keep running as long as i gave it gas. let it drop down to idle and it would die out. it could not be restatred while hot. wait 20 -30 mins and it would restart
anyone got any ideas
 

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the decompressioner is built into the camshaft and keeps the exhaust valve open just a bit .
getting it hot several times has most likely warped or egg-shaped the piston or cylinder wall
 

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Discussion Starter #7
I figured out my problem.
i did a leakdown test and everything with the motor looked good so i went back and tore down the carb for the third time.
i found that during the rebuild i placed the upper ring (on the jet needle) below the lower ring so when the spring was installed in the throttle valve diaphram it was not actually holding the jet needle down. i swapped the parts back to where they actually belong and it is running fantastic.
thanks for any/all help
 
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