I would post this question in the engine forum, but I think you guys have much more experience with this engine. I have an O.S. .61 RF-P (tuned pipe) that seems to eat a glow plug about every other time I go to the field. I put in three flights when I go fly, so I get about six flights (1.5-2 weeks) from a plug. I am using 15% nitro (with castor, of course) and have tried many different O.S. plugs. Here are my observations:

[ul][*] From the look of the plugs the engine seems to be tuned perfectly (not too lean or rich).[*] The coils turn slightly dull and a few starts later they die completely (with igniter).[*] The coils do not appear to be deformed or shorted.
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I had another pattern guy take a look and he was as baffled as me.
I've never had an engine do this to me before. In fact, I have two RF-P's and this is the only one eating plugs. It's getting expensive! [:@]