Runaway 430

Hello all,

A bit of background and how the runaway occurred...

I have a 1981 430wr that I purchased this summer. Since I purchased the bike the idle has been pretty high once the engine warmed up, though fine at cold start. About 3 weeks ago I went to replace the plastic Clark tank that was on the bike when I bought it with an aluminum tank that also came with the bike. I ended switching back to the plastic tank as it turned out I was missing a needed bolt. Anyhow, here is where things started going south.

I went to start the bike up and just couldn't get it to start. I figured I'd come back to it when I had some free time, which was today. To my surprise the bike fired right up and I figured I had just flooded it 3 weeks ago and all was fine. I rode up and down the street, went back to my house to park it, turned the fuel off and rode around my house property waiting for the bike to die due to lack of fuel. After about 30 seconds the engine ran-away... full throttle rpm type thing! I hit the kill switch and NOTHING. Dump the clutch and held the brakes but was unable to kill it. Dropped the bike on its side and grabbed the shifter with my hand and started bumping it up to 5th. This killed the engine finally.

What could this be? An air leak most likely as the throttle cable seems fine. I know 2 things for sure at this point. The bike had a high idle once warm and I recently switched tanks around possibly getting something into the carb. Thoughts?

Thanks,
Jeff

After reading up on this a bit, it appears that turning the petcock to off could have aided in the engine running away as it creates a lean environment for the engine. Does this seem reasonable to you folks?

I'm actually a bit nervous to fire that thing up at this point.

-Jeff

you never want to turn off fuel to starve a two stroke...after hitting the kill switch, turn on the choke and apply throttle or just leave choke on. this usually shuts them off. after that pull plug wire.
you likely have an air leak already, and running it out of gas got the head hot enough to "go diesel"...hopefully the engine isnt being damaged...a 2 stroke that idles high for no apparent reason says LEAN

AIR leak. check your intake boot for cracks.

Check your spark arrestor is not blocked, that caused mine to run away

My Maico did this. Was an air leak.....

I had a KDX250 (don't ask) that did this, it was ignition side crank seal. My inlet rubber on my '88 400 has cracks but no leaks......yet. May have to use some polyurethane to fill the cracks.

Thanks for the feedback guys. I'll start tracking down the air leak and go from there. The runaway lasted for around 5-10 seconds. It's hard to tell really since it all seemed to happen so fast. The piston isn't seized and the kick-start cycles normally. I'll check for leaks, see what I find and then try starting the bike up and see how it goes.

try to track down a good deal on the single shock aluminum intake, then you can use plain mikuni 2 bolt cheap intakes..they pop up on ebay cheap at times..the single shock ones angle to the side and dual shocks do not. same for 250-430..not sure when they came stock, thought the 87-88 bikes already had em...

My shopping list is growing, but I need to add one of these, thank you!

I have an 82 430. It was running bad, sounded lean at idled high and broke up in higher rpms. It would idle pretty high but never to the point where it was screaming. My problem turned out to be the screws in the plate for the crank seal behind the ignition were backing out and it was sucking air thru the gasket behind the plate. I put gasket sealer on the gasket and no more problem. Probably not your problem but wouldn't hurt to check it.

Well, I checked the bike out and see no "obvious" air leak spots. I fired the bike up to see if any noticeable damage had occurred from the runaway and the bike fired right up and seemed to be fine. At this point I believe I got the engine shutdown before any damage was done.

I don't know the history of the engine and have always wanted to try a top end rebuild on a two-stroke. So, I think at this point I'm going to give it a shot and replace all seals while I have the bike torn down and rebuild the carburetor while I'm at it. It's getting too cold to ride up here in Alaska anyhow! Should be a fun winter project and will give me a chance to get to know the bike.

I'll probably have quite a few questions as I attempt the new piston/rings and seals so bear with me.

Thanks again everyone,
Jeff

better to be safe than sorry.

Just as an aside, if a motor starts to run away like that ,turn the bike upside down taking care to avoid the spinning tire and chain. Turning it upside down takes fuel away from all the jets and stops the engine immediately. The bike won't run on air alone.

start a new thread with pics when you are ready!

Is that a single wire kill switch Jeff ?
If so you might like to run another wire from under the switch to an earth on the frame.
Have seen these not work because of the steering head bearings interfering.

Check using a leak down test before you do anything else.

This. Even if you do not have an air leak, running a two stroke with the fuel off will cause a lean condition and it can run away just as if it has an air leak. If you want to drain the carb for storage, just unscrew the plug on the bottom of the float bowl instead of running it until it runs out.

I agree, running a two stroke out of fuel until it stops is a bit like draining the sump on a four stroke while running the carb dry, there is almost NO lubrication for too long, would anyone do that on a four stroke? I doubt it.

Tony.