RE: Working for a 4-2-4 break
The FP series wasn't designed for the 4-2 break, but there have been some (Len Neumann and others) that have had some success in modding the engines for this type run. Not worth the trouble and time, IMHO!
You didn't state your prop; you might load the engine with a bit more prop and get it to break, then the real problem with the FP series will become obvious; it won't want to go back to a four stroke. Some just use a fairly large dia. prop with flat pitch (3.5 or 4 inch) and run the FPs in a rich two stroke.
The OS LAS 46 is the only one of the common OS engines that is used with any success without lots of mods. On my LA 46 engines, I use 10/22 fuel (Morgan is now mixing a fine CL 10/22 blend), the original OS plug or a T bolt RC Long, a current production ST 51 NVA installed in the venturi, an APC 12.25x3.75 prop and launch at about 9000-91000 (depends on your location/altitude). Something less than 5 oz. for the pattern and I get a noticable break when pointing the nose up before launch and in most of the maneuvers.