HELP! My 426 died...

Last night I pulled the left crankcase cover off and replaced the stock flywheel with a weighted one. I laid the bike over at about a 45 degree angle to the right the entire time so I wouldn't leak out oil everywhere. After letting the Yamabond dry for a couple hours, I stood it back up and left it there the rest of the night. This morning I went to take it for a ride. It started easily as it normally does, and I took off. I only made it about a half a mile before it started to bog down, then died. As I was still rolling, I put it in second, popped the clutch, and it roll started. I was able to limp along at a little above idle speed for another 1/4 mile, but then it died completely. Had to push it back home. I had some difficulties starting the bike a year ago when I first bought it, a couple times after tipping it over and fouling the plug. So today, as soon as I got back home, I pulled the plug. It looked fine. It didn't look wet at all. I replaced it with a new one anyway, and it kicks over easily but won't fire up. The plug is sparking appropriately. So I took the carb apart and inspected the jets to see if they were plugged. They are all clean as can be. The bowl was full (before I drained it), and nothing seemed abnormal in the carb that I could see. Air filter was just cleaned a few days ago. I can't see what is missing here. Here is a pic of the plug (poor quality, sorry I only have my phone camera here)...


I thought I read sometime ago, that occasionally when these bikes get laid over or crash, that sometimes an air bubble gets trapped in the Carb. I'm not sure of this, but I've heard of it......maybe it's a possibility??

Is it possible that somehow the Woodruff key got damaged/lost/loosened, whatever, and now your timing is way off? I know there have been issues with woodruff keys getting busted etc.

hope this helps....

Is it possible that somehow the Woodruff key got damaged/lost/loosened, whatever, and now your timing is way off? I know there have been issues with woodruff keys getting busted etc.

That would be my guess.

Bubbles can't get stuck in carbs.

I will pull it apart and check the woodruff key. But if this were the problem, wouldn't the spark plug be wet?

I just pulled the cover off again. Flywheel is still on the shaft in the proper position, with the woodruff key in place.

Come to think of it, it had been intermittently acting a little funny the last time I rode it around the neighborhood, just a few days ago. I washed it and cleaned the air filter. When I started it up after the washing, it would only run on choke for about 2 minutes. Take it off choke or give it any throttle and it would die immediately. Once it warmed up, it seemed to run fine like usual. I thought it was just a fluke thing. But maybe it was just a precursor to today's events... I didn't even really wash it, just kind of lightly rinsed it off with no high pressure at all. It is really acting like it is starving for fuel...

Nevermind, I am an idiot. When I inspected the flywheel earlier, I didn't pull it off because I had to borrow my neighbo's puller. I looked down the shaft and saw the woodruf key in the grrove, and it seemed tight on the shaft. But when I pulled it off just now, I found that te woodruff key had sheared in half. That explains why it ran OK for a minute, then died. So, I am getting a new woodruff key. Is this a common breakage point with a weighted flywheel? Thanks again, flintlock and gray. Amazing how you guys can diagnose a problem that I am in denial about without even seeing the bike...

Even a blind squirrel finds a nut once in a while. :thumbsup:

Shearing keys isn't really a huge deal with YZFs, with or without a weighted wheel. You may have gotten the key rocked out of place and then undertorqued the flywheel as a result.

Be sure the tapers on the crank and flywheel are in good shape and try again.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now