I used Max55AX in a Butterfly for 3D fly. Frankly, it is better than what i have before. But in the past two weeks, it suffered unexpected quit in the Torque roll, and last weekend the lead to a quite serious crash.</p>

The engine quit when the torque roll begin (from level fly to the plane vertical), before this happen I leaned the mixture since the engine seems too rich to get a prompt accelerate. Maybe the quit is leaded by this adjustment.</p>

The quit trouble me a lot besides the plane repair. Max55 is easy to adjustment and stable for normal fly. But the mixture adjustment method defined in the mannual is too simple and not accurate for 3D fly purpose. I have try other common method for mixture adjustment as cut the fuel during idle, but it do not contributive lot.</p>

I had a 40LA when i am a beginner, the method for mixture adjustment show in the manual is very good. The engine just go the way like what descripes in the manual. (I know 55AX works difficult than 40LA in air).</p>

BTW, i wonder whether 55AX is too big for the 40Class Butterfly, which makes the 55AX works at 1/3 throttle during torque, and the engine is easier to quit in the low throttle than in high throttle.
Furthermore, I also experienced a quit when the engine set to a rich mixture in torque.</p>

I use 13X4 prop for it, theRPM is around 12,000 and I rich the needle to around 11,200 for fly. Fuel is coolpower15%.

Could you kindly show me a little detail way for mixture adjustment than what in the manual? Especially for torque roll, should we set it a little rich or use an on-board glow ignition equipment and trigger it for additional power supply fo glow during torque roll?

(P.S. Ichecked thethreads inforum, it seemscoolpowerfuelisthecause, is that right?)</p>

When an airplane is in a vertical attitude, the fuel system is what can give a lot of trouble.  Fuel draw will be diminished because the engine must pull fuel straight up from the fuel tank.  If the engine is running at reduced throttle, then fuel draw is also lowered because the engine will have less vacuum to draw fuel.  If the airplane is so light that a very low throttle setting is used to hold a vertical line, then you may need to use crankcase pressure with a fuel regulator to insure good fuel supply to the engine.  With just muffler pressure to the fuel tank, it would not be abnormal for an engine to quit after a bit of running with the airplane in a vertical attitude.

The brand of fuel would not be the cause of your engine's quitting.

The setting procedure detailed in the O.S. manual is a good one.  You can also hold the airplane vertical and adjust the high-speed needle so that the engine is a bit rich of peak RPM when running at full throttle.  Adjust the idle on the ground for good idle RPM and good throttle transition.  After that, there's little else to do.

<font size="4"><font face="Courier New">Bax,
Thanks for your prompt reply and detail explanation<span class="737034301-11062009">!

Would it be better if a two-stroke 46 or four-stoke 70 set for this application? Especially, four-stroke engine is more recommended for 3D, why? </span></font></font>

Almost any engine that has good throttle response will work well.  There is no "correct" engine for your application because many different engines work.  A four-stroke engine would not necessarily be a better choice.  People will use what they have.