Got a 55AX. Sweet Motor. Just ran a tank through it on the ground as directed by manual. I did the break in procedure. My question is, it says for three flights, avoid successive nose up flights. Why ?

I'm guessing it is because the head pressure in the fuel lines when nose up will create a slightly leaner condition.

What they're saying is that after the first tank of fuel you can fly with care because the engine still needs more time running in. The first 3-4 flights should be done with a rich mixture where the engine has only just barely gone into a clean 2 stroke. This will likely be around 1500-2000 revs below fully peaked out. The "nose up" caution is to avoid the engine running too lean because in a nose up condition the fuel level drops well below the carb level, especially as the tank empties. After those 3-4 flights it still needs another 5-6 flights of running in but gradually leaning the mixture after each of those flights. So in all, the engine needs around 10 tanks of fuel before it can be considered to be fully run in. Assuming a tank gives about 10 minutes of flying time that means around 1 1/2 hours of running in which is a far cry from the usual suggestions of run it rich for a tank then fly the snot out of it . The better you run them in the longer they'll last.

I hear ya. Thanks again. I guess that means there wont be any 3D flying for a while.

I believe their reference to" nose up" means not to hang it on the prop. That adds excessive load & heat to a new motor. The motor has a pressure tap on the exhaust that pressurizes the tank, thus the motor shouldnt know the difference if its nose is up (or down) & cause a lean condition. Just dont hang it on the prop for a few tanks & you'll be ok....Gene