Two-stroke engine runaway!! YZ250

YZ250 that had had a mouse nest inside it, skunking everything up. A combination of things caused a lean situation that caused the engine to rev uncontrollably. Kill-switch didn't work as it was dieseling. Check my channel for the build of this YZ250 and making it what it should be!

Basically the bike was running extremely lean. It wasn't getting enough fuel but way too much air. So it caused it to diesel with the carbon build up on the inside of the cylinder. Hence why the stop button didn't work. When I rev'd the bike, the lean situation stopped, cooling it and the button finally worked. This happened a few more times and in those situations I couldn't stop the lean situation, I had to gear into 5th, holding the front brake, and drop the clutch. Dirty carb from a mouse chewing through the filter, and the float being set incorrectly all contributed to them.

[backroadrevival]

You could hear the engine start to lean out before it ran away

[boblitwinsandymateer]

Had the same thing happen to me last weekend on a vintage MX bike...the bike kept screaming even after I pulled the spark plug wire...either the piston developed a hot spot or the plug did...drop it into gear and dump the clutch with the breaks on...

[erbengottijr]

This happen to my honda250r I was like wth then I found this vid thanks my bro now I gonna work on my bike and get this problem fixed🤙

[MatthewWright]

Your sniffles at the very end are the best😂👌🏾 every biker gets them😂

[lordvader]

This happen to me once with a 85sx. threw in a whole new engine off ebay lol, started first kick and started revving uncontrollably, kill switch wasn't hooked up so i grabbed the spark plug boot, accidentally ripped it off due to getting the shit shocked out of me, the engine was still running from an solid 2 inch purple electric arc from the shredded spark plug wire to the spark plug and top of the head. Finally found something nonconductive to more the plug wire and the engine died. Finished that bike up and never had any issues, she was a lil ripper.

[turbofiat]

The car in my icon is a Trabant 601 with a 2 stroke 600cc engine. One day I was trying to get this electronic ignition kit functioning and was messing around with the timing. I had the idle speed jacked up to keep the car running and had the timing advanced too far. I decided to take a break so when I went to shut the engine off, the battery light came on but the engine kept running. This car has a gravity feed fuel system, tank inside the engine compartment! In order to kill the engine, I pulled the air cleaner hose off the carburetor and laid my hand over it and killed it that way. My guess is due to the advanced timing, the carbon buildup on the cylinder heads or piston crowns must have been acting as a glow plug. I almost shat myself!

[valium]

Has this happen to my pitbike 70cc. Its a semi auto so i put it in neutral and from that you can go straight to 4th so i did that and quickly shut if off. Scary stuff man. Bike was ok thanks to quick thinking. Subscribed 👍🏻

[UriwaLukisa]

it sounded like in windows, your audio stucks before giving blue screen lmao. if anyone remember, windows xp was full of blue screens and the audio and video was getting stuck for a while before it 😂
(jokes aside, as a bike rider, this is definitely a situation you definitely dont wanna be in)

[rod]

Mine does this when low on gas I'm thinking because it's two stroke and gets less oil which raises the octane like giving it more throttle I guess

[shredder_mang]

It’s possible you might of had a leak in one of your case seals like the one in between the magneto and the case or the one on the clutch side behind the main gear

[samurboi]

This happened when we had float and check valve issues on my rotax max 125cc, i switched off the ignition and it kept screaming and we had to hold down brakes and cover the airbox

[RonnieMacJr]

My brothers crank seals went out while I was on his bike put er in 5th and dump the clutch sure gets your heart racing!

[RC-nqmg]

If that is a 2 stroke gassoline engine with fuel oil lubrication, it't not really a true run away. A run away is when the engine consumes its lubrication oil as fuel becausr of over filling or some failure, turbos like to puke lubrication oil into the intake when they fail. What happened here is called dieseling. Caused by overheating, the engine can burn its fuel without an ignition source when it gets hot enough for the heat from the engine and the cylinder compression to exceed the flashpoint of the fuel. it can also happen from hot spots from carbon deposits and in rare cases from crank case oil in a four stroke due to blow by if the engine gets really hot. It is most common in engines with fuel supplies that are naturally aspirated, gravity fed, or mechanically pumped, and introduced into the intake via a carburetor. since the fuel delivery is unrelated to electrical power supplied by the ignition circuit, and the carburetor is mainly passively and mechanically controlled. In engines with pure electrical ignition, the fuel pump and injectors will shut down, starving the fuel supply so the dieseling will only last a handfull of seconds, unless its consuming crank case oil. In that case it is closer to a runaway.

[xjlover]

Happened to me and i was in 4th gear by the time i pulled the clutch it was too late. Messed myself up pretty good.

[tominagy]

Did you get a solution to this? I have the same thing happening on my KTM exc 200 even when it idles. Started after a long ride, also it dies when I try to accelerate like it doesn't get enough gas or air.

[gimli]

iv just had this happen to me today on a Honda MTX, i hit the kill switch nothing happened i then pulled the spark plug cable off and it still kept running away, the only way to stop it running was to remove the fillter and put my hand over it

[panueldunuel]

Damn that's soo lean, no surprise it happened 😂

[aye]

That last breath at the end I can feel the pain 😢 😮

[bilalmahomed]

Hey I had my PE250 do that once. It reved up to max and refused to switch off with the kill switch and even taking off the spark plug wire. I was convinced that this bike was possessed! Then I hit the choke and that killed it.

[liam-uynz]

I can’t tell if my bike has this but I’ll be driving all fine then all of a sudden it shoots off full throttle without touching it