Engine wont start. Could it be the Decomp system?

1 reply to this topic
  • mxer829

Posted June 04, 2009 - 12:29 PM


Ok, so I have a 2004 YFZ450 (I know, its a quad and this is a mx fourm but its for the girlfriend and I need help badly).

I cant get the engine to run with just the stock battery power, I need to jump start it with a car. I've bought a new battery and it been charged and tested. I also bought a new starter but I'm not sure how to test that... The quad does run very well once I get it started also, it just needs to be pull started or jumped from a car.

How will I know if the auto decomp is working properly and could it be bad? Whenever there is pressure on the pin (in the cam), the "arm" (that moves outwards as the RPM's go up) is hard to move at first. Once I put enough pressure to move it, there is a "click", like pin was stuck, but this is only when there is pressure on the pin as it would be when holding the valve open. When there isn’t any pressure on the pin everything moves freely. Is this normal?

When I press the starter button, there is a large draw on the battery. It moves from 12.8 volts to the high 9's or low 10's. After the initial crank the volts level back out at about 11.

I just checked the valves and they are in spec (intake clearance is .125-.150 and exhaust is .203 on both sides).

Any ideas?

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  • KevB

Posted June 05, 2009 - 01:51 PM


Check there is spark... if there is it should start, if there is not, then try a new plug... after that start looking at the electrics. I once had a problem of mud/water in my kill switch which prevented the bike from running...


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