What can you tell me about this engine for stunt?  OS Max SF .61.  Was RC now has a .278" venturi with a ST needle.  Prop?  The price was right.

I think we've all heard of it but discounted it as a stunt engine as being too heavy and to high strung. Heck, I couldn't even get an acceptable stunt run out of my SF-46. Guess you may be on your own with this one.  

Edit: Changed "stunt fun" to "stun run"...Freudian slip maybe?...ya think?

Thanks BB.  I need the nose weight as this plane has an extremely short nose.  I'll see if I can tame it with soe shims under the head.  I might have to lower the ports.

Sleepy,
I haven't worked with this engine specifically, but have worked with the 46 SF and the 55AX successfully.
For the 61 I would simply add one head Gasket and use a .270 venturi with a ST or PA needle valve assembly.  
The .278 venturi you mentioned might be OK but if it is a little too "lively" you might simply try a couple of layers of panty hose material held over the venturi with and o-ring.  My guess is it will give a descent fast four run on a 13 X 4APC or Bolly 12.5 or 13 X 4.25 three blade.  I wouldn't expect it to be a great stunt run but acceptable.  I would use a tongue muffler and pressure to a uniflo tank and block some of the holes as necessary by tapping them for 4-40 screws if needed to tame things down some.  Bear in mind if you go too far with this it could cause the engine to run HOT!  I would expect this engine to produce a trememdous amount of power compared to a typical stunt engine.
I would look for an RPM range of about 9400 to 9600 to start for launch speed.
Might be worth a try if you really want the weight.
This thing would likely turn a 14 inch Prop with ease if you have the ground clearance...line tension should be no problem...
I would expect about 6.5 oz of fuel consumption of 10% nitro fuel for the pattern.  A 7oz tank could be necessary.
I'd be interested in hearing about the results.

Randy Cuberly.