Being 'modified' I'm not sure what to expect but on the stock engine I'd try a 10-4 running a rich 2 cycle at launch.  Like the .40,  don't plan on a 4-2 break on the motor.  The FP wasn't meant for this and aren't happy being force fed the four cycle.  Just let it run like a little turbine and adjust flight speed with prop pitch.  Perhaps the  'mods' are one of those attempts to make it break.  Usually not too successful.  For an off the shelf choice the APC or wood Power Point should work acceptably.

Dave

My stocker loves the Top Flite Power Point 10x4 and an OS#8 plug on 10/22 fuel. That's with a 38 ounce plane. I launch with a wet 2 stroke.
Rusty

Hi Robin,

To follow up with Steve's post, Tom sets up engines to do a traditional 4-2 break.  As Steve says, a 10"-10 1/2" prop with 5"-6" pitch and releasing at around 9000 rpm will probably be a good starting point.

   I would also suggest maybe looking for a stock piston/liner. This should provide much better performance, as there wasn't much wrong with the engine in the first place. For whatever reason, the 35FP runs much better, stock, than the 40FP, even with all the same parts (i.e. venturi/muffler). I flew my ST46 airplane with a 35FP back in the pre-tuned pipe era and while it wasn't quite as good as my *very strong* ST46, but it was better than an average ST46. I seem to recall using an 11-4 Taipan and a Rev-up 12-4 cut down to 11.5 and cleaned up drastically. Maybe 10200 launch RPM (or about 2000 rpm faster than the ST46...).

    It also ran OK with an 11-6 Rev-Up, but run that way it was no match for the ST.

    Brett

Very much obliged fellas for your contributions.

She seems to like a Bolly prop' ..... 10.5 x 5 at the moment on the bench testing.

When the wind has dropped and when the grass is cut at our Club field I'll be out there !

Thanks again ,

Robin