I have experienced this problem on the downline when flying large motors. I first installed a velocity stack to help the motor get more air. My problem came on the downwind line. It was apparent that the velocity stack was forcing too much air into the intake. I turned it 45 degrees down and that really helped. The motor quit sagging untill I made a hard downline and pulled up abruptly. It seemed to be happening all over again. I tuned and tuned. I checked with the guys at
http://webpages.charter.net/rsengineconversions/

We talked and tried the motor with and without the veloicty stack. What we finally ended up doing was turn the stack UP about 45 degrees. It appears that what was happening was when I pulled up abruptly the slippage of the plane towards the ground was putting the plane in such a situation that I was again forcing too much air into the intake. Now my motor runs like a scalded dog no matter what attitude. It runs as well inverted as it does uprightand straight up or down it really scoots. Those guys really know their GASSERS ! It's pulling my Hangar Nine Ultra Stick like a dream and for pennies a day.

Big Al