Ran the WR450 out of water!!!!

Okay. My kid ran his 04 WR450 into a tree at an enduro this past weekend, smashed the radiator on the left side and cracked the top tank. We gambled and tried to get it back to the next reset/gas before the water ran out.

We lost the gamble and the bike died 2 miles before the gas stop.

It rolls over, so it didn't sieze.

It seems to have good compression, but with the auto decomp I'm not sure I'm getting a good feel for it.And I haven't done a true comp test yet.

It has spark and seems to have fuel too, so I ruled out any kind of overheat sensor that it might have.

There is a plastic plug in the head that faces forward just above the header that is now leaking oil onto the header. I imagine it got hot enough to melt that enough to leak. What is that plug for?

My guess is a blown head gasket or a cracked head.

I'm looking for suggestions from the hardcore yamaha 4stroke mechanics what to look for. I am very familiar with 4st bike motors, but not the 450 yamaha.

Tear it apart and take a look. If you're very familiar with 4 strokes then you should know what you're looking at. There's nothing exotic about these motors.

The plug you refer to is where the manual decompression lever used to connect - they used the same head after going to auto decomp, oil will leak out of there if the plug is gone.

You might have gotten lucky - I'm guessing you blew a gasket.

only way to see what's what is to start tearing it down.

After checking the flywheek key and that being okay, I was baffled. It still missed on idle, would just die sometimes and was hard to start.

I cleaned the carb 3 times and still had no luck. It was just like the idle circuit was plugged or not working.

Then it accurred to me that a friend of mine had the same bike and I could swap carbs and other parts to eliminate or pin point the problem. We swapped out the carb with no difference at all. Next I was going to swap the CDI unit, then I looked at the plug cap/coil unit and thought it was easy to try. Swapped it and it ran like it was brand new! I swapped it back and forth a few times to make sure I didn't just disrupt a wire.

It's the coil for sure! It makes sense that the overheat killed the coil, seeing that it is part of the plug cap. It's too bad I took the whole top end off.

The good news is my son gets to ride Stumpjumper now. :thumbsup:

Thanks for all of your help and suggestions.

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