Question about 2004 KTM SX 450 racing

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Bike wont start

My 450 sx just quit running last winter.Noticed a loss of compression.After looking at the bike I noticed that when I kick it over the bike is sucking air through the exhaust and pushing air out of the carb.I am mechanically inclined but i dont really know what to do fix it.Any reply would help thanx. First badass dirtbike i have ever owned looking to get it fixed.

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  • bandit9882 Dec 30, 2008

    thanx for the reply clute735 i am looking foward to giving it a shot



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Hi , This sounds suspiciously like a valv problem. Maybe a valve got bent and is stuck open. If you are mechanicly inclined , are you up to the job of removing the rocker cover for a look?? If you are do this and with the spark plug removed turn the engine over and see what the valves etc are doing. Also worth checking is , your cam chain is ok, valve timing.
Is there any binding when the piston reaches TDC. Is it maybe hitting a valve?
If you are not sure about this stuff tho. Take it to a shop.
Hope this helps.

Posted on Dec 29, 2008


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An easy DIY compression test is to remove the spark plug, place a finger over the plug hole and press down on the kick start lever. The air should be forced past your finger at a high rate and you should hear the air escapeing. You must not be able to prevent any air from escaping.

Good luck


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