My wifes 2003 Auto Vinson has developed a new problem. At low speeds, runs great, no problems. It wont get past 38mph for some reason. Seems to sputter some at that speed. Not certain if it is hitting rev limiter or there is some other problem. Air cleaner/plug/belt inspected and OK.

Any suggestions?

 

How old is the gas?
Could also be a plugged main jet. Drop the float bowl and inspect for crud...if you find some, the jets need to be cleaned out.

 

Pull the fuel line from the carb, turn petcock to prime and make sure you have good fuel flow. There is a screen in the carb inlet fitting. Use a peice of wire to clean it but don't poke the wire thru it.