Trusty WR450 died and left me stranded!

I was riding rough gnarly trails all day. I popped over another fallen log and my '07 WR450 (all stock except the GYTR unplug and jetting kit) did a cough and die. I hit the button and the engine just spun over real easy and fast. After several attempts, I swung out the kick starter and gave a couple of stabs. Uh oh, way too easy. Plenty of spark and fuel, but seems like no compression. Get out the rope get dragged 25 miles back to the truck by a KTM and listen to jokes the whole way home.

What happened to my WR? It was running perfect up until that point.

Thanks.

Edited by cardoc

I might be wrong but maybe the auto decompression is stuck open not allowing enough compression to build?

valve problem? That would explain no compression building etc... but on an 07, that would be really harsh man

What does it take to check the auto compression release?

check the carb vent hoses. the second day i owned mine it did the same thing and it ended up having some wet sand in one of the vent hoses. Took it home cleaned the bike and end of the hose and fired right up.

Man, I hate hearing stuff like this. My only consolation is that my 08 has never had a valve even move with over 3000miles. Let us know what you find...

Sparkplug Pop Out?

wow that is crazy,that does sound like a valve,did you pull plug and look at?maybee something happened to piston.

Check your hot start lever and plunger to make sure it's not stuck.

Sounds like you should pull the valve cover and check the timing Chain and valves. pull the plug first and see if you can see anything on the piston and make sure it moves.

let us know what you find

Check your hot start lever and plunger to make sure it's not stuck.

Surely that would make it harder to kick, not easier.. The more air you introduce during startup, the harder the bike is to kick.. Try kicking it at WOT and you'll see what I mean..

Neither hot start nor throttle position have any effect on how hard or easy it is to kick over the motor.

Cardoc, any updates on the initial problem? Hqve you looked at it yet?

The more air you introduce during startup, the harder the bike is to kick..
not true

Thanks for the info and ideas. I have ridden Yamaha four strokes for years and they have proven to be rock solid reliable. That's why this was weird. I finally took it apart and here is what happened. First of all - IT WASN'T THE BIKES FAULT! Several months ago I was riding in Baja and by fluke, a branch got jammed between my shock body and the frame. It damaged the plastic air boot/air box. I have since, cleaned it all up and have been riding it with no issues. Well, it turns out, a small broken piece of plastic from the broken air box, after all this time, found it's way through the carb and down into the seat of one of the intake valves and held the valve open - no compression. Removed the small piece of plastic, new head gasket, checked everything else, put it all together and good as new! My fault or a fluke branch - whatever you want to call it. Thanks again for the input.

wow...would have never thought of that happening... glad it was a plastic part...

Ingested plastic and still runs...gotta love these Yamahas.

Wow, very interesting.

I had just bought a new 09 WR450F because I had heard how reliable they were and just after that, yours was one of the first posts I saw on thumpertalk! I thought ... AHHHH :smirk:

Amazing to hear you could get it going again with no real damage.

Whew.

So what did you find dude? We're dying to know what makes a bike just stop running and then not seem to have any compression.

So what did you find dude? We're dying to know what makes a bike just stop running and then not seem to have any compression.

did you read post 14 ???

What he said... post 14 tells the story. Thanks!

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