I recently purchased a 1986 procraft 1540v with an evinrude vro 90hp. The motor is starting and running without issue. At top end it’s only revving to around 4000 rpm. It goes thru momentary “full revs” if that makes sense. Like it wants to fully open up but it hangs at about 4000. This is my 1st outboard and I want to learn the stuff myself. Any suggestions would be appreciated.