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rmz250 wont start


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Hey guys sorry if I could of found this elsewhere but I couldn't seem to find anything . so I've got a 2006 rmz250 that won't go since it was rebuilt it has fuel it has spark but it didn't have compression(even without auto decomp) and valve clearances were all right. I'm guessing it isn't piston or rings as their brand new but I'm not saying it isn't them . I have the head off now but how do I check valves to make sure its not them?

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The basic things to fire off, minimum 100lbs compression, spark and fuel. 

 

Did you check for spark initially during the time you were trying to start it? 

 

Check for fuel.

 

Timing that will prevent it from starting.

 

Piston/Rings installed correctly?

 

Taking the head off will require a new head gasket and making sure it is torqued to the correct specs.

 

New plug as well I would recommend.

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Yeah checked spark first and deffinately getting fuel but just backfiring. It had no compression at all and timing marks were all right . even checked to make sure the gear on the exhaust cam hadn't slipped as I've heard its common on these and its fine too . got fresh gaskets and plug ready. What plug would you say was right also as I'm using a ngk br8eg I think it is that I was told was the correct one for the bike and I always thought it was right but now I have the head off I see it doesn't quite reach as far as I'd expect it to ... Sorry for rambling on haha

Edited by tomsk15
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Turn the head upside down with a spark plug in it and fill the chamber with gas.  If it drains right out your valves are not sealing.  Or if you have a small flashlight you can shine it in the intake/exhaust in a dark room and look for light bleeding out out around the valves.

Edited by motogotro
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Are you sure the keyway on your flywheel is installed correctly?  If the key is missing or sheered the valves will look like they are in time but because the flywheel will be out of time with the piston you won't have any compression and it will be firing at he wrong time which can cause the backfiring.

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OK I'll give that a try and yeah I thought that at first so I put a blunt screwdriver down the plug hole and it was at its highest point when the marks where their

 

That's a good check so if that is at least close then the keyway probably isn't your problem.

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  • 1 month later...

Okay guys back again so valves are now correct and have compression(not sure how much due to auto decomp but it's enough to be able to hear it when you release the pressure from the gauge) and I have spark .. Is their a way to make sure the carb is working correctly or start it without carb to see if it is that? Sorry if that's confusing

Edited by tomsk15
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Only other thing I can think of is obviously on the flywheel timing marks theirs one by itself and then further round theirs 2 next to each other , when I got it back from being rebuilt it was on the single mark but I didn't think that was right and the valves were meeting the piston, so I set it the right side one of the 2 together after reading a tutorial about it, I also had a screwdriver in the plug hole to make sure it was at it highest point .. Is that the right mark to have it on?

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