Re: 1968 johnson no top end speed
When you open the throttle more air is introduced. If the proper amount of fuel isn't delivered at the same time it will hesitate and not run properly. It could be as simple as an obstruction in one of the jets. There are so many orifices in a carburetor that should be clean as a whistle I would try a thorough cleaning of the carburetor by disassembly first before spending money on a rebuild kit. Another thing to check is any synchronization linkage your motor might have.
