Sorry that was a typo. it is an fx. no, I was not aware the old models had a problem with the valve. What's odd is the gentleman I bought it from had no problems with it. I've set it to the factory setting of 2 turns in on the high speed and 2mm at full throttle on the low speed. I flew it earlier today and it wouldn't give me anything higher than half throttle. Also shuts off in a climb.