Sounds like your engine is running rich and flooding the plug out, specially when its not tuned to the new fuel u bought. Clear the crank of floods and any other oils thats in there by putting it upside down and cranking it for like a minute or two. Lean the LSN by 1/4 try starting it again, this time try keep your engine alive aslong as you can by reving it with abit of throttle. If it dies after the igniter is taken out, try keep it there for longer, rev it more and lean the LSN more until it idles safely

The moment you just idle there in 1 spot the engine will load up with oil because its rich and put out the plug as soon as you accelerate so you have to clear the engine out once in a while by revving it at least half throttle. So try giving it abit of throttle when your starting and while tuning.

Your using a hot type glowplug right?