engine backfiring - Polaris ATV Forum
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post #1 of 11 (permalink) Old 12-09-2009, 04:01 PM Thread Starter
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Post engine backfiring

1994 400l two stroke. I just had the piston and rings replaced because i lost compression. After the parts were replaced it started to backfire and wont stay running. Any idea what the problem could be. Thanks for your help.
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post #2 of 11 (permalink) Old 12-09-2009, 04:54 PM
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sounds like you are either getting too much fuel or too little fuel.

how long has it been since anything has been done with the carbs?
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post #3 of 11 (permalink) Old 12-09-2009, 05:41 PM Thread Starter
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when the piston was replaced, earlier this this week. the carb was cleaned and jet was cleaned.
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post #4 of 11 (permalink) Old 12-09-2009, 06:37 PM
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and im guessing whoever jetted it did so according to relevant temperature and elevation for where the quad is?

was the carb pressure checked before it was installed again?
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post #5 of 11 (permalink) Old 12-17-2009, 04:26 PM
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Check the carb boot where it mounts to the cylinder. After pulling the carb, I had one that the rubber cracked and was pulling air around it. They get brittle with heat and age.

95 Magnum 425 4x4 , 518HO carb & air box, 12inch rear wheel conversion.

02 Magnum 500 RMK

If it ain't broke, I can't afford it!
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post #6 of 11 (permalink) Old 12-19-2009, 04:47 AM Thread Starter
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would the boot cracked also prevent from firing at all?
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post #7 of 11 (permalink) Old 12-19-2009, 09:09 AM
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If it is bad enough then yes. I would tear down the carb and inspect for trash or gumming, 2 stroke carb are bad about that after they sit the oil from the gas being mixed will gum up the carb. If its not starting first put a new spark plug(bad about fouling), if still nothing take off your air box and spray a shot of starting fluid into the back of the carb, if it tries starting you then know you need to go through the carb. Do not use a lot of starting fluid to try and keep it running, it has no oil and could cause engine damage.

95 Magnum 425 4x4 , 518HO carb & air box, 12inch rear wheel conversion.

02 Magnum 500 RMK

If it ain't broke, I can't afford it!
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post #8 of 11 (permalink) Old 12-24-2009, 08:01 AM
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Sounds like piston in backwards to me!!
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post #9 of 11 (permalink) Old 12-24-2009, 08:14 AM
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or reed valve damaged/broke
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post #10 of 11 (permalink) Old 01-01-2010, 08:39 AM
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The piston can be installed either way. I've seen it put in backwards-the engine won't run.
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