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]

I'm still waiting for the OP to come back and reply if he found the problem or not and if not, post some pictures as I had previously requested as I refuse to do any troubleshooting whilst shooting in the dark not even seeing if there is anything that is obvious to the rest of us that may be causing his problems.

 

[2smokerr]

haha, thanks, appreciate the support, i’ve been building for a awhile, pics aren’t gonna help on this one!

 

[2smokerr]

If a guy is positive there is no air leaks, then run on has to be detonation. But, seeing @2smokerr is only on his 3rd tank of fuel, that's not enough to cause a significant amount of carbon build up. Time to check the torque on everything.

It definitely seems like an air leak causing hot spot but honestly at this point the next step for checking air leak is to split the cases and tear everything down and check the mating surfaces and gaskets

 

[DAMIEN1307]

haha, thanks, appreciate the support, i’ve been building for a awhile, pics aren’t gonna help on this one!

Suit yourself...lol...You would be surprised how many ASE certified master mechanic/technicians are on this forum that might have been able to help you with that problem other than myself.

We have had just pictures to go by that have solved many a similar problem as yours...Amaziing what another set of eyes on problems just might see that the builder has missed or just didn't know it mattered.

 

[2smokerr]

Suit yourself...lol...You would be surprised how many ASE certified master mechanic/technicians are on this forum that might have been able to help you with that problem other than myself.

We have had just pictures to go by that have solved many a similar problem as yours...Amaziing what another set of eyes on problems just might see that the builder has missed or just didn't know it mattered.

Of course a second set of eyes is good, and if you’d really like, I can take some pics, and of course I won’t turn down help
from someone more experienced, but it seems pretty clear that this is not something identifiable by pictures.

 

[DAMIEN1307]

Of course a second set of eyes is good, and if you’d really like, I can take some pics, and of course I won’t turn down help
from someone more experienced, but it seems pretty clear that this is not something identifiable by pictures.

Just let a fellow Bostonian "Masshole" put another set of eyes on it...Who knows, maybe something will jump out at me...lol...lol.

 

[Johnny_]

Just let a fellow Bostonian "as$hole" put another set of eyes on it...

Wait what'd you just call yourself...

 

[DAMIEN1307]

Wait what'd you just call yourself...

It said "Masshole" Johnny...lol...It is an "affectionate" term used for people who are, or were formerly from the Commonwealth of Massachusetts...lol...Hence the term MASS-hole...lol.

 

[Chainlube]

It definitely seems like an air leak causing hot spot but honestly at this point the next step for checking air leak is to split the cases and tear everything down and check the mating surfaces and gaskets

Before you break the whole thing down, get a spray bottle full of water. Run the engine and spray the whole engine down methodically. Start at the bottom where the cases meet, some times the gasket has been compromised and is sucking air. Work your way up, if it stalls, there's the leak.

 

[Gazorp]

My experience with two cycle dirt bikes had me witness several bikes that did this. As Chainlube suggest, look for air leaks.

Those motors were put together with liquid gasket material that looked like silver tooth paste. Every now and then the person who assembled the particular motor didn't get an even coat or an air bubble that led to the problem. I don't know that much about how these motors are put together yet. But air leaks are air leaks.