1. Your question is unclear.... How does it spin 180? How does it land on its roof by the rear end dropping?!
When jumping, you should accelerate up the face of the jump and maintain a fixed throttle position, (whatever you left the jump with) and try and land with the same throttle position. Resist the temptation to lift off the throttle, only doing so gently to bring the nose down if at all necessary.
2. Reducing motor timing will reduce speed and temperatures. Increasing motor timing will increase speed and temperatures. A reduction of 5 degrees will only generally be small effect however. 30 deg should be fine though.