Can't Start The 2008 YZ250F

Son's 2008 YZ250F. Here's the story,

Completely rebuilt top and bottom end over a year ago.

5 weeks ago, kept stalling at Glen Helen. Finally would not start.

4 weeks ago took it to a shop (friend) started and ran fine.

Went to Comp Edge and rode all day.

This Thursday and Friday night kicked it all night would not start.

Kick 10-12 times, rest, go back and kick again. Get a loud back fire and that's all.

Sat night it started once and ran but stopped and won't start again.

I know it can't be fixed over the internet but any suggestions (well most) will be welcome.

What I have tried:

New stator

New coil

New plug

Replaced CDI

Unplugged neutral sensor

Checked/unplugged kill switch

Continuity check all wires and connectors

Never see a spark with plug removed and gnded

Disassembled carb and reassembled

Shimmed valves, none were out of spec, three of five were boarder line.

New clutch basket and hub (not related but just a mention).

Can the flywheel go bad? It took a beating when the motor blew and has some shallow gouges on the inside.

I see it is two pieces pressed together with a raised strip on the outside for the pick-up pulse generator.

There seems to be four magnets inbetween the peices, can feel them with a steel bar as I slide it around the inside diameter.

My son is so bummed. Can't ride for weeks. Can't sell a bike that won't start.

So does it have spark or not?

Do you have a manual?

Yamaha manual has a series of tests for each of the electrical components that pretty much anyone with half a clue and a multi meter can do.

That how I found my mates stator was rooted on his 450F.

When he had the engine rebuilt the mechanic reused the lock-washer for the flywheel and one of the fold over tabs had broken off and stuck to the magnet inside the flywheel

So does it have spark or not?

Do you have a manual?

Yamaha manual has a series of tests for each of the electrical components that pretty much anyone with half a clue and a multi meter can do.

That how I found my mates stator was rooted on his 450F.

When he had the engine rebuilt the mechanic reused the lock-washer for the flywheel and one of the fold over tabs had broken off and stuck to the magnet inside the flywheel

Yea, went through all the resistance tests in the manual and determined the stator needed to be replaced. Still won't start most of the time. Does it have spark...I have never been able to see any spark from the removed plug but it has started and it does backfire.

If the stator is bad or not putting out power then you won't have power going to the ignition system which means no spark.

It may be time to replace your stator, I recommend Ricky Stator all day and night. They're good people, and it shows from them being in business for so long.

If the stator is bad or not putting out power then you won't have power going to the ignition system which means no spark.

It may be time to replace your stator, I recommend Ricky Stator all day and night. They're good people, and it shows from them being in business for so long.

Thanks for the suggestion. I know my OP was pretty long to read thru but I have tried everything including replacing the stator.

Had a friend's 2001 yz250f go through similar issues in Baja last year. Eventual fix was to replace the magneto. Amazingly a local shop is who diagnosed the problem and they even had one there from an old bike that worked.

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