I haven't needed to use more than a medium heat range plug and the engines would work fine, I rarely use anything but a Fox glow plug in my engines. On some occassions I used a Fox Miracle plug though. For competition I usually had to go with a more cool heat range glow plug. In your case I suspect the glow plug may be defective or worn out. Some engines tend to eat a glow plug or two during break in, due to the tiny bits of metal coming loose as the engine wears in. The other situation is bad glow fuel too. What kind of glow fuel are you using?

Someone makes the glow plugs inRussia. Norvel USA imports one here http://www.nvengines.com/index.php?p...&Itemid=67

The Cyclon Engine people also sells glow plugs http://www.rusengines.ru/?lang=en

I think the folks who sell the Parra Engines and others also sell the Russian glow plugs too http://www.clubtamaran.com/material.htm