I ran my converted Webra .91 today with a Graupner 14x11
Muffler-----Davis SoundMaster 90 size
Carb-------MDS 9mm C1 from MDS 1.48
Fuel--------Davis ABC
Prop-------Graupner 14x11 two blade
RPM--------7,550, I could coax 7,680 out of it but that was leaning on it a little too hard by the sounds it made. This is an older engine, ABN I believe. As a glow it would turn an APC 14x6 at just under 10,000.

Dave,

The 14x11 you are using is a much greater load on the engine, than is a 14x6. Yet if the engine turned the 14x6 at 10,000, it was releasing 1.49 HP, compared to the 14x11 at 7,550, which is only 1.18 HP. The Diesel is giving more torque, despite the lower calculated HP, giving 21% less HP at 24% less RPM.

I would suggest a larger prop than you are using, in the range of 15x10 to 16x12.
Also, the carburettor you are using is too large for a Diesel. A 7mm bore carburettor should fulfill this engines fuel needs.

Using too large a carburettor makes you lose power and consistency.

With a much larger prop and smaller carburettor, the Diesel will excell.

I'm going to have to redo the test, when I removed the engine from the PSP the backplate was loose, this was obviously my fault. About 1/3 of the gasket had blown out and was gone so I cleaned it all up with alcohol and replaced the gasket with UltraCopper.

Hobbsy a 14x6 equiv 13x7? i ran the 13 x8 will put alittle more time on it before a lean run
it may run very close to the webra with the same prop that was quite a pickup on diesel
.Did you cut the branchs and roots off the tree before mounting it?

Dieseldan, do you have the early Webra .91 like mine or the new lighter, more compact one? The new one is really cool looking.