I'm sorry you are having troubles with your O.S. First I have to say do not give up on the AX engines; either there is some small thing that is not right, or there is a small possibility something is wrong with the engine, in which case Hobby Services will more than hold up their end of the warranty, and very quickly.

I think the most important thing to do is to get the engine running properly without the fuel pump, pressure line for the Perry pump closed off, and with the tank near the firewall. Return the engine to it's starting settings (high speed needle 3 full turns open, mixture screw flush with the throttle housing). From what I read above the engine has not really had some good running time for break in. It will probably have a slightly boggy transition for a few tanks of fuel. Don't adjust the low end until you've had a good amount of fuel through the engine. When you're satisfied with the top end, you can start working on the mixture screw to adjust the transition. If you don't do this before you hook up the pump, you will never get accurate settings and have a really tough time getting a good transition.

Once your needles are at least really close to the right setting, you can reinstall the pump. The idea is to tune the pump to the engine's settings, not try and tune the needles to the pump. When everything is setup properly, the mixture valve will control the idle, the pump will affect the transition, and the high speed needle will control the top end.

I think the best thing for you to do is post something in the O.S. support forum here on RCU. There are lots of guys, including reps from O.S. who will be more than happy to walk you through a checklist of things to get your engine working right.

I have bought like 4 AX engines in the past year, and am about to buy another one for my Venus 40. They have been so great to me that I can't justify buying something else in a two stroke. I'm sure you will get your problem solved and will end up happy with your 75AX.

Good Luck!