Sometime ago in the BVM Tips and hints section this was published....



Ducted Fan glow plug coil adjustment


If your D/F engine is a bit fussy in the idle and throttle-up mode - here's an easy fix. Use a fine tool such as a dental pick to pull the coil out of its chamber about 1/16".
This brings the ignition source closer to the center of the combustion chamber and allows the engine to throttle-up more reliably even with a mixture that is slightly rich.
Check the coil position after one flight to be sure you haven't over done it. We have had success with this technique with both the McCoy 9 and K&B H.P. glow plugs.


http://www.bvmjets.com/

I read somewhere else that this adjustment should be preformed ater you heat the plug first as it will soften the plug coil and make it eaiser to strectch the coil without possible damage....

Rod