The 55 AX has the needle on the carb, and it runs right. The rear needle engines are a huge pain in the butt. I will never buy one again. I went through 5 91 FX engines and a couple of 46 FX engines and all went back to the factory and they finally just gave my money back.

I ran the new 55AX a few weeks ago and it ran like an OS used to. Right out of the box, flipped it, it started, adjusted the needle just a tiny bit and flew it a few flights. It ran like a top. The FX never produced power and quit every flight, over heated and had major fuel flow problems. I am sure the new ones are not much better.

Some have good luck with them. You can roll the dice and hope you get a good one, or get a 55 AX and not worry at all.