I have a great running ST 90 that was on a SIG 4 Star 60. It was mounted upright. I took the engine off and put it on another airplane in which the engine is canted approx. 135 degrees. Test flew it today and it seems to not transition too well after doing all the high/low speed needle settings. It seems to transition poorly.
Question: I know 2 strokes do not like to be inverted, however, should this affect the performance of the engine at 135 degrees? If so, what are my options? glow driver?
The position of the fuel tank seems to be correct also.
Another Question: I'm running a APC 13X8 which works well for sport flying, however, I want to do some 3D. What is a good prop for 3D?

You could try adjusting the angle of the sprar bar as the Tigres can be adjusted to tweak their mid-range a bit.

Try one of these: http://www3.towerhobbies.com/cgi-bin...?&I=LXGAE5&P=0

Yes try the spray bar. You may also be rich on the low end. Inverted engines are more sensitive to a rich mixture. It could be your low was rich the whole time and you did not notice it until the head was tilted down. A hotter plug may also help with this. I have run several good 3D props on a 90. I like the 13x6MA for fast spool up on a light plane. I have also used a 15x4W. It's a good choice on a little heavier plane. It may also work well on the light plane but I don't have the ground clearance.

David