I have a couple of questions:
I have had my Fox 74 for some time now and got it to work properly in the past. This past weekend I tried it on a different plane that has had other engines flying it with no problems. With the Fox 74, I could tune the top rpms to over 11K with an MVVS muffler (similar performance to Fox stock mff.), 12x6 XOAR prop, and 5% nitro fuel (17% synth, 3% castor). However, when I tilted the plane upwards to check for lean runs, it would lean out easily. So, I ended up having to richen the HSN 2000 rpms lower. With that rich setting, the engine was too weak to power the plane and max rpms were a mere 9300 only. Can anybody suggest any ideas where to look? The engine would still run hot even with 5% nitro, 2 head shims, new head button, and 12x6 prop. It just seems the engine doesn't have enough fuel suction/pressurization and it is still sensitive to heating. Compression, bearings, idle, and throttle response are good, only the top end is weak.
Secondly, I ended up swapping planes with somebody and the plane I got has a Fox 45. Does the 45 require low nitro like the 74? Anything I should watch out for? Compression and bearings seem good, but no muffler.