I have found only two engines that were not amenaable to operation on glow/gas fuel. Sometime back I discussed the problems I was having with a Stihl 35 cc and a Shindawa 23 cc. Both of these engines had an "effective compression ratio of better than 13/1. I tried several fuel mixes to get the highest octane possible that would still run without constant battery power on the glow plug and in addition several different glow plugs with heat ranges from cold to hot. I was never able to get either of these engines to run without significant vibration in the 4000-5500 rpm range. These problems all pointed to signification ignition advance in this rpm range. I am flying both engines currently, but am operating them on EI syncrospark. Operating in this manner both engines are well behaved and mid-range vibration is minimal.

The reason I mention these two engines is that they both have significantly higher "effective compression ratio" than other engines that I have operating of glow/gas. The engines that I have operating on glow/gas are: Homelite 25cc, Mac 28cc, Mac32 cc, Echo 38cc and a Zenoah 40cc. All are well behaved and quite powerful, but all have an effective compression ratio of less than 10/1.