I have an OS max 10 in an airplane that has well over a hundred flights on it. I flew it several times yesterday. I use a master airscrew 8-4, which performs very well on this airplane. It will idle down so that you can almost see the prop turning, and with 2 ¼ inch diameter wheels it takes off from a grass strip. I have used both Omega 10%nitro and Red Max 15% nitro fuel. The glow plug is a Fox with idle bar. I suspect you are running it a little lean. I always adjust just a little rich of peak RPM, and have had no trouble with either overheating, or cutting out at idle. A seven inch diameter propeller will certainly let the engine rev a little higher, however the thrust will not necessarily be more. Be patient breaking it in and you will have a great little engine that will give you years of service.