I wouldn't celebrate just yet. The engine is dying when you remove the booster battery from the glow plug. Something still isn't right.

I'm with someone else that suggested that you check the screen that filters the fuel. Surging is usually a sign insufficient fuel flow.

Glow fuel doesn't go "bad" unless you leave the cap off for hours at a time, or let it catch sunlight directly. I doubt that was the cure. Nitro helps any engine, so that part of it was a possibility. These low compression utility engines will burn just about any flammable liquid without protest. I have ran mine on Coleman Fuel. It doesn't get much worse than that.

I'm still trying to figure out the fascination with this mode of running a gas engine. Let's see, you take a perfectly good running gasoline fueled engine and then you ruin it? <G>