The Brodak 15 is a very nice all-around stunt/sport engine.
When I wrote the operating instructions, I made an error in the fuel requirements.
I mentioned 5 to 15% nitro - you can, in fact, go as high as 25% nitro without any issues.
Do not run straight castor - a good oil blend is 50/50 castor/synthetic but the engine seems happier with less castor and more synthetic. 30/70 is fine.
Don't look for a 2/4 break - it won't happen unless you lower the compression with an extra head shim or two. That will cost you some power.
Keep in mind however that the engine was designed to run on the lean side and in the tests I've run, that's where it performs best.
Experiment with different props in the 7 to 8 inch diameter range and different pitches to see what works best for you.
I've had very good results with the 8-6 Top-Flite wood.
The break-in time varies. After around 20 minutes total time, slowly lean it out until it stops. If it stops abruptly (like seizing), it needs more time. If it just leans out and dies, it's ready to fly.
Bob Z.