Good morning. I have a 91 Johnson 25 hp tiller that seems to go into some type of limp mode after warmed up. Plugs are like new, brand new fuel line, primer bulb, fuel tank, and fuel. It starts right up and will rev right up until it reaches operating temp, then begins to surge almost like a car reaching it's rev limiter. If I back off the throttle it will idle very rough and almost want to stall. I've read about possible over temp issue causing things like this. Does my engine have these sensors? Is there anything that sounds common to this problem other than normal carb issues? Thanks in advance for your help!