Yamaha 70hp 2-stroke Overheating

Hello. I just bought a "rebuilt" Yamaha 70hp 2-stroke. I believe it's a 2001 model. When I have the fuel enrichment set to normal the boat runs rough and will over heat after about 5 minutes. If I switch it to open it will run without overheating but it doesn't perform as well as I expected it to. It topped out at 30mph which is about the same I was getting with a 50hp on the same boat.



The water flow seems good so I'm stumped as to why it's overheating. My thought was maybe it's running lean in the normal setting so it overheats but when set to open it's getting more fuel so doesn't have the problem. I may be way off with that diagnosis.... Any suggestions?

Thanks!

Just so I understand. The fuel enrichment. Is that the choke?

We fixed it. The guy I bought it from said he cleaned the carbs and put a new impeller in it. He lied... The jets were filthy and the impeller was old and had all but two of the flanges broken off. We cleaned the carbs and replaced the impeller. Runs pretty good now with the enrichment valve set to normal. Still only get about 31mph out of it though which doesn't seem right.