My 91 90hp losses power when I run over 30mph. I've had it to the dealer and it ran fine in their tank. The dealer used his own gas tank to test it and let me borrow the tank to run it on the lake. It ran fine on his tank. After returning his tank, I hooked my inboard tank up and the problem continued. I have replaced the line from the tank to the motor including the primer. Talking to the dealer, he suggested running with the vent tube disconnected. Did that, same problem. I've pumped the tank out, put in fresh gas, and changed the plugs. I have nylon/plastic Mercury style connectors between the boat & the motor. Is it possible that one of the connectors isn't letting enough fuel through at high speeds. The dealer's tank had an aluminum female end...
Glad it's operating right. Companies(and us) trying to save a few pennies and we suffer.