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Hello. I was putting the first ride on a new top end on my bike last Thursday. I landed an jump and my bike bogged out like it ran out of gas. I assumed it fouled the plug and went to change it. When I got to my car I took the plug out and it had great spark. I tore into it the next day. Everything in the carb seemed fine. I took the air filter off, still wouldn’t start. I checked to see if the reed valves were damaged, nope. I even took the exhaust off to see if it had somehow clogged. After all this I still can’t figure out what is wrong with it. I poured some gas down the spark plug hole and it still wouldn’t run. There is no reason why this bike shouldn’t run yet it won’t. Any and all help will be appreciated. My only guesses is there’s something up with the carb or there’s no spark under compression. I’m grasping at straws here.

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2 hours ago, Brodyyz144 said:

I landed an jump and my bike bogged out like it ran out of gas.

I see it's your 1st post, Welcome to the forums Brody!

 

Last season I had a very similar failure on my 2010 YZ125, 

following a hard landing, the engine bogged and died, wouldn't re-start and, backfired once loudly.

Pushed it back to the truck, pretty much tear the bike apart and go thru everything,

it's getting fuel, spark (despite hard to see in daylight), all electrical connections ok etc.

 

So by the time I'm done checking everything, the engine components have since cooled off quite a bit. 

It now re-starts, I head back on the track, didn't even get one full lap that on the same jump, the same thing happens again.

This time it won't re-start, I pack up and head back home (just happens to be at the furthest track I ride at, 5 hours of driving for 2-3 laps ridden...)

 

Following day, without checking anything, the engine starts-up fine,

I go for a test ride on a nearby dirt road, after 10 minutes of riding the engine cuts-out and dies.

Push it into my shop, it's still getting spark yet I feel it's not as strong as it should be.

Once it's fully cooled down, it re-starts and again after a brief ride, simply dies.

 

Get the multimeter out, I test all electrical components as per service manual, the ignition coil shows it's out-of-specs.

Go to dealership, compare readings on a brand new coil, it shows the same bad values as mine! (error in the manual?)

 

Ends up it's the CDI unit (which can't be tested so an expensive last resort gamble if everything electrical checks out ok) 

Replaced and the bike starts and runs fine since.

 

Not saying you have the same issue but, keep in mind a CDI unit can fail in weird ways and, still show a decent spark despite not starting/running.

I did find a lot of sand packed into the CDI harness connector which I suspect probably held in moisture, perhaps a contributor to the failure.

 

 

Edited by mlatour
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57 minutes ago, mlatour said:

 

Not saying you have the same issue but, keep in mind a CDI unit can fail in weird ways and, still show a faint spark despite not starting/running.

 

 

That is a good suggestion, but it seems to have very good spark. It couldn’t be many other things though so I’ll look into it. Thanks 

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8 hours ago, Brodyyz144 said:

I haven’t messed with the fllywheel yet, but the timing seemed to be correct 

 

It probably only takes 5° off to mess things up to the point it won't start.

If it's anything like my 2010, basic timing starting point is set by lining up the stator plate, flywheel and engraved lines in the case but,

the only way to confirm it's correct is with a dial indicator in the spark plug hole and, making sure all the marks line up

when the piston is at a specific distance before top dead center (specs in service manual)

 

As Budlite suggested, pull the flywheel and inspect the woodruff key, cheaper than buying ignition components (that can't be returned)

Edited by mlatour
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  • 1 month later...

Well I know it’s been a while but I got the new coils, still nothing. Although I noticed it’s making a weird huffing noise out of the exhaust when I kick it over. I’ve been dreading the idea of getting a new ecu but  I think I’m going to have to.

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