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YZ 250 Won't Start After Rebuild


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Hi all.

Just completed top end rebuild and clutch plate replacement.I didn't get chance to run it straight away & bike stood for couple of weeks and now went to run it and just won't go.Fuel is making its way to the plug which also has a spark.

Any advice??????

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I'm guessing you have premix/assembly oil pooled up in the crankcase. Same thing happened to me on my last rebuild. If the compression was low enough to prevent the bike from starting you'd probably feel it with your foot.

My advice: Remove the spark plug and turn the bike all the way upside down (fuel tank removed of course.) Place a crate under the rear fender so the cylinder is pointing straight at the ground. Pump the kickstarter and watch for gunky looking gas blowing out the spark plug hole. If there is, keep pumping until nothing comes out (or even longer.) Return the bike to its wheels and let it sit for a few hours with sparkplug out. Try starting it then.

Money back guarantee.

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I'm guessing you have premix/assembly oil pooled up in the crankcase. Same thing happened to me on my last rebuild. If the compression was low enough to prevent the bike from starting you'd probably feel it with your foot.

My advice: Remove the spark plug and turn the bike all the way upside down (fuel tank removed of course.) Place a crate under the rear fender so the cylinder is pointing straight at the ground. Pump the kickstarter and watch for gunky looking gas blowing out the spark plug hole. If there is, keep pumping until nothing comes out (or even longer.) Return the bike to its wheels and let it sit for a few hours with sparkplug out. Try starting it then.

Money back guarantee.

Not true, My buddies 03 blew a ring and we didn't know it but when we were kicking it over compression seemed great from the feel of our foot. We were kicking it over for a good 30 minutes thinking it was just flooded at the time. When we ripped it apart the ring was pinched in the piston with a chunk of it missing.

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I had the exact same problem - I am 99% convinced that you've got cleaning fluid, oil, etc built up in the cases.

Remove the plug

Turn OFF the fuel

Kick the bike crazy hard with the throttle WIDE OPEN for some time

Clean and install the plug

Turn the fuel ON

Kick the bike with wide open throttle again

It'll start - trust me 🙂

Berg

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Thanks for the advice.Bike started 2nd kick after draining cylinder.

Few funny looks with bike hanging from gantry,but good result.

Time to hit the tracks.

Good to hear all is well. When I encountered the problem it certainly had me scratching my head too.

How much fluid came out? Barely any fluid was in mine, though it still prevented the bike from starting.

Berg

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I had the exact same problem - I am 99% convinced that you've got cleaning fluid, oil, etc built up in the cases.

Remove the plug

Turn OFF the fuel

Kick the bike crazy hard with the throttle WIDE OPEN for some time

Clean and install the plug

Turn the fuel ON

Kick the bike with wide open throttle again

It'll start - trust me 😏

Berg

Another trick is to:

Take out plug

Turn on gas

Stick in 2nd gear

Open throttle WFO

And push around the yard for 150ft

Reinstall plug

put chock on

Kick like normal

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