Anthony:

While I don't have high regard for the LA engines, too many people have them running well for me to dismiss them entirely.

So, questions. Can you stop the engine by leaning it out while the glow heat is on? And does it run all its fuel out before quitting with the glow heat on?

If both are "Yes" you probably haven't found the right plug, or your fuel is contaminated - stored, got water in it.

If you can't stop it by going lean you have a carb problem, or the tank is too high. If it wont run the tank out with glow heat on I'd be looking at the fuel.

Hope this helps.

Bill.