04 yz450f starting problems....

4 replies to this topic
  • floatingk

Posted March 25, 2010 - 01:26 PM


so Im trying to get this beast to start to no avail. heres the history and work Ive done so far:

Two winters ago I put in some new piston rings and slapped the top back on and everything was super in spec. Not having the time I never started it or broke it in. Now moving from NM to Cali I brought the bike and cleaned out the gross carb that was lacquered up from old gas, changed the oil and filter, re-jetted for the 3000 elev from the leaner 7000+ jetting and rechecked the timing and valves. New plug. The only thing it does is a random backfire once in a while. It feels like it has some compression but with the auto decompress it seems hard to tell. I dont get it. could it be a stuck decompressor weight? It has spark and I disconnected the stop button just in case (happened before with corrosion).

Roll starting doesnt do a thing. Anybody have an idea? Im about ready to drink more beer than is wise at this point. That or part it out.:thumbsup:


  • JandJ07

Posted March 25, 2010 - 03:31 PM


It sounds like it is too rich, with the explosion in the exhaust. If its flooded from being too rich it can wash the cylinder walls with fuel...decreasing compression. Although since it never ran from the last time you had it apart it would be a good idea to check the compression as well.

A problem with your pilot circuit could cause a rich starting condition.

If your exhaust cam is out of time this could cause the decreased compression.

Probably just gonna need to start digging.
Spark plug condition(Fouled from excessive fuel)
Cam Timing

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  • floatingk

Posted March 25, 2010 - 03:56 PM


well I found 1 exhaust and 1 intake valve pretty far out of spec once I got the right gauge. thanks for the input.

  • JandJ07

Posted March 25, 2010 - 04:09 PM


well I found 1 exhaust and 1 intake valve pretty far out of spec once I got the right gauge. thanks for the input.

Your valve clearance does need to be set properly, but is probably not causing your starting problem...unless they are way out.

  • floatingk

Posted March 25, 2010 - 05:01 PM


holy jeebus! I had no idea that valve clearance worked like that. I put the cover back on and was working the kickstart slowly to ease in the cams and first thing I noticed was how much more resistance there was. Second it started! with a quarter motion. Wow!

Thanks for the help guys!

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