Runaway 2 stroke

[2smokerr]

Runaway on Zeda80​

I have what seems to be a pretty unique problem. Sometimes after a few heavy pulls, and engine will start to rev super high, despite being off the throttle. The kill switch won't kill it, which makes me think it's not just an air leak causing a lean condition. Something is allowing the fuel to ignine without the spark. It's not a faulty kill switch, as once I fully ripped the wires out to disconnected the ignition circuit when I saw killswitch wasn't working. Obviously choking it out or stalling was the only way to kill it. So i'm wondering if it's just getting super hot and auto igniting, but generally it seems the mix is pretty rich, it never needs choke to start even when cold, and if I have choke on it's too rich to start. It smokes a decent amount, but i've yet to do a plug chop. Maybe it's too lean at full throttle, and not at idle when starting, there is a bit of a bog at WOT, but I can't tell if it's bc rich or lean. My only other thought is that maybe it's just way too high compression and that's causing the auto ignition, it's really hard to kickstart unless you get a good run up, so it's clearly pretty high compressio. Have not done a squish gap test yet. Running single base gasket.

 

[DAMIEN1307]

Runaway on Zeda80​

I have what seems to be a pretty unique problem. Sometimes after a few heavy pulls, and engine will start to rev super high, despite being off the throttle. The kill switch won't kill it, which makes me think it's not just an air leak causing a lean condition. Something is allowing the fuel to ignine without the spark. It's not a faulty kill switch, as once I fully ripped the wires out to disconnected the ignition circuit when I saw killswitch wasn't working. Obviously choking it out or stalling was the only way to kill it. So i'm wondering if it's just getting super hot and auto igniting, but generally it seems the mix is pretty rich, it never needs choke to start even when cold, and if I have choke on it's too rich to start. It smokes a decent amount, but i've yet to do a plug chop. Maybe it's too lean at full throttle, and not at idle when starting, there is a bit of a bog at WOT, but I can't tell if it's bc rich or lean. My only other thought is that maybe it's just way too high compression and that's causing the auto ignition, it's really hard to kickstart unless you get a good run up, so it's clearly pretty high compressio. Have not done a squish gap test yet. Running single base gasket.

Time to take some really good all around pictures of you motor and the bike it is mounted to so we can see if what is happening is visually obvious to seasoned builders.

Ps...Your from Boston, I am originally from "Southie" a retired police lieutenant now residing in Alamogordo, NM
Welcome to the forums.

 

[Chainlube]

New engine or is it broke in? If you have been running it for awhile, then it could have a bit of carbon buildup in the head. When you do a sustained pull at WOT it will super heat the carbon and it will glow red hot, or hot enough to ignite the fuel without electricity. Pull your head and check it out.

 

[Darwin]

Reminds me of 60's/70's cars that you used to shut off the ignition and they'd keep running for 5 minutes. You're sitting there wondering WTF.

 

[Wrench]

Reminds me of 60's/70's cars that you used to shut off the ignition and they'd keep running for 5 minutes. You're sitting there wondering WTF.

My girlfriend in Hawaii had a 70 Buick Apollo 2 door, she paid $100 bucks for
She had the car for about 1 year until I bought her a 74 Fiat Spider convertible $3k in 86

Buick always ran and when ya turned the key off it kept running for another minute or 2 Then when it finally stopped running
You could hear the valve clatter and a big fart then a sigh of relief - clunk clunk clatter clatter pop ahhhhhhhh

 

[DAMIEN1307]

You could hear the valve clatter and a big fart then a sigh of relief - clunk clunk clatter clatter pop ahhhhhhhh

Ahh, you must have heard me in the bathroom this morning...lol...lol.

 

[Johnny_]

His problem sounds like some people. You politely ask em' to stop talking or whatever the case may be, and they just won't quit.

 

[Darwin]

His problem sounds like some people. You politely ask em' to stop talking or whatever the case may be, and they just won't quit.

Wait till you get married, you ain't seen nuffin yet! Only way to shut them up is to surrender. Yes Dear, you're right. Then you get to hear, what do you mean I'm right?

 

[Gordy]

Wait till you get married, you ain't seen nuffin yet! Only way to shut them up is to surrender. Yes Dear, you're right. Then you get to hear, what do you mean I'm right?

View: https://youtu.be/VJsMVSFzRSc?si=Y7txc_XMR1KW1D_J

View: https://youtu.be/T_Km11HNzUY?si=AIUpAVd2WWd_Grb9

 

[Amwicr]

could it be that at stupid high rpms the thickness of the kill switch wire isnt enough to interrupt it somehow

Deff sounds like an air leak regardless