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1978 KM100 starting problem

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Hey guys, I have this little km100 bike that was running strong the other day... Then it randomly just stopped and shut off, and now wont start. I had some issue with the kickstarter after feeling like it was getting jammed then would work again. I thought i might have shattered a piston or something (happened to me before) so i took apart the top end and everything is perfect. I bought this bike rebuilt and everything looks new. I reassembled it, put in another new plug try to kick it and it wont start, after about 5-6 kicks it makes a quick loud pressure noise, almost the sound of when you unhook your compressor line. then it smells a little bit like fuel and exhaust..cant get this thing to start anyone have an idea? 

 

Notes:

 

1978 KM100

Full engine rebuilt was working perfectly fine 

oil injected 2-stroke

I do use a little pre-mix to make sure it gets oil,im weary of the oil injection 

 

Help me please! would love to get this bike out to the cottage next weekend and have some fun 

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The timing may be way off.  Sounds like its backfiring.  Double check that for starters.

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The timing may be way off.  Sounds like its backfiring.  Double check that for starters.

Thanks Dan, ill get looking and see. Is the timing something that could just randomly screw up?

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Anything is possible.  Something may have worked loose and moved.  That thing should have points which can get out of whack pretty easy.

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Anything is possible.  Something may have worked loose and moved.  That thing should have points which can get out of whack pretty easy.

 

To be honest I have never worked on a stator or points before, my dad always was my "mechanic" haha anything I should be looking for, or any pointers before I get in there? and before I start watching youtube videos haha!

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I think you're going to have to pull the flywheel off to even get a look at them.  You might be able to check timing without taking it apart.  What I would try would be to pull the spark plug out and leave it connected to the plug wire and rest it on the cylinder head.  Then you can insert a wooden dowel or pencil into the plug hole to give you an idea of where the piston is at in the stroke.  Then you can slowly turn the engine over with the ignition on and observe when the spark fires relative to the travel of the piston.  The spark should fire when the piston is pretty much at the top of the stroke.  I think the spec for ignition advance is 24 degrees before top dead center.  The piston should be just shy of top dead center at that point, very near the top of the stroke.  If the spark is firing before the piston is at the top of the stroke it is likely to kick back or backfire. 

 

Its also possible its firing 180 degrees out and lighting off the fuel/air mix while the transfer ports are still open.  That would cause the high pressure sound you're describing.  Points are mechanical, they can do strange things.

Edited by turbo dan
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