Originally Posted by
Cougar429
Still primarily suspect a pressure problem or you have a restriction in the carb line.
One thing to remember is that the Fox 74 will require a lot more fuel at full throttle than any of the previously mentioned motors.
What happened with the 55AX, (cannot add question marks till I figure out what format changed on the keyboard. All I get is É).
I did re-run the 74 on the bench with a stock MVVS muffler, which is similar in performance to the Fox stock muffler. The engine maxed at 11000 rpms with 5% or 0% nitro fuel. I was only running a 12x6 prop though. Despite that, it felt quite hot after a short run with relatively cool ambient temps (in the upper 40's) and I was using a cooler OS #8 plug instead of the previous Miracle plug. But, I examined the fuel tank on the plane and it had the plastic tubing instead of aluminum or brass. The plastic tubing has a considerably smaller inner diameter, so that might explain the leaning out when holding the plane upwards. I replaced the tank tubing with brass tubes with big inner diameters.