ORIGINAL: DarZeelon
This does not mean it will not run with it on 15% with this plug, but you will need to excessively richen the mixture (open the needles), for the engine to run properly...
The running costs of glow engines seem to be taken for granted, by manufacturers, retailers and modelers alike, under the false pretense that 'this is a hobby'...
In glow engines, the needles are the engine's primary 'ignition timing controls', during the run (the plug's heat range is one of the static controls).
A leaner mixture will ignite sooner, the flame would propagate more rapidly and it burns faster too.
So, closing the needles is the same as advancing the spark...
A 'lean-run' is simply detonation; not oil starvation...
So, you need to open the needles further, to compensate for the excessively high heat-range of the glow-plug, just splattering that expensive extra fuel all over the place, with no advantage whatsoever!
Ken,