Well, it's a "puzzler" for sure. The only thing I can think of is that perhaps the methanol, either your pure stock or once it was mixed with the glow fuel, absorbed water. Alcohol is hygroscopic and absorbs water right out of the air. So if your can was open for a while, especially if it was humid, it might have gotten some moisture in it.

Sorry, but that's the only possibility that comes to mind.....

Well, two more thoughts.... Try changing the glow plug. I have had weird, strange problems disappear with the change of a glow plug on many engines over the years.

Second. Are you sure the engine is able to run rich enough on the Gas/Glow mix?? On a few carbs, I have had to raise the metering lever in the regulator a touch to get them to richen up enough to run well on Gas/Glow. The mixture for Gas/Glow is necessarily richer than that for straight gasoline/oil, and might just account for your problem.

Good luck and let us know how it works out,
AV8TOR