2003 sportsman 500 HO not starting-backfires - ATVConnection.com ATV Enthusiast Community



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Old 06-14-2018, 08:10 PM
Weekend Warrior
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Default 2003 sportsman 500 HO not starting-backfires

The sportsman will not start for me. It turns over no problem using the starter. Iíll crank it for a while then eventually make a loud pop noise. The air seems to come through the carb.

i got it to run briefly yesterday using starter fluid. That was short lived. I could not get it to start after that using starter fluid.

one weird thing i noticed. After trying to start it for a while using the start button the engine just wouldnít move. I forgives this was due to me drawing on the battery. So i went to use the pull start. It was solid, would not move. After a decent amount of time passes i use the cord and it moves again.

-I checked compression,80 psi.
-it has a spark, replaced the spark plug
-i checked fuel flow. Itís not a heavy flow but itís moving the gas. I cleaned the fuel pump. Just dusty no mud.
-i removed and cleaned the carb.
-I removed and cleaned the starter. One of the brushes was stuck.
-battery is good. About a year old.
-Air-filter is nice and clean
-new gas
-i pulled the valve cover off. Everything moves, no metal or grinding noise
-i checked the fly wheel and itís proper mounted (no sheared key)
Iím about to remove the engine and start looking inside. Any help would be greatly appreciated!!
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Old 06-15-2018, 11:22 AM
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Sounds like lobes worn down on the camshaft. Throwing it out of time.
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Old 06-15-2018, 11:31 AM
Weekend Warrior
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I was starting to look into the timing. With worn lobrs would mean cam replacement?
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Old 06-15-2018, 11:42 AM
Powerranger262's Avatar
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Yes. Happened to my boss's 04 700. Same symptoms, backfiring through the carb and all. Was told that the metal that the cam was made out of was a softer metal, and wore down easily.
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Old 06-15-2018, 11:44 AM
Weekend Warrior
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Thank you for the info. Iím gonna get the motor out today and peel it apart.
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Old 06-15-2018, 01:29 PM
Weekend Warrior
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Any recommendations for a good engine kit ?? Other than Polaris !
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Old 06-15-2018, 03:26 PM
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The soft cams were mainly an issue on the 1996-2000 Sportsman 500s, before they made the 500 H.O.s with a different cam. It's rare to hear of anything outside of that range having have soft cams.
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Old 06-16-2018, 09:38 PM
Weekend Warrior
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Ok, I took it apart and measured the lobes. They are all with in spec.
I noticed heavy carbon on the piston head and cylinder head. Iím assuming itís normal but figured i would mention it.

Should i check anything else prior to putting it back together.

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