Re: Mercruiser 260 help
 

Did you try a different tach and see if it reads the same? I have a 1985 23 Nova with the same power as you and my guage only shows I'm running 3,900 rpm's and I hooked up our box (tool box w/ full guages that plugs into the main harness on the engine) and I'm reading a max of 4,600-4,700 rpm's on that tach. Maybe that is the problem and not necessarily the engine is not turning all the rpm's. Just an idea.
Brandon

Re: Mercruiser 260 help
 

What is the total ignition timing? What vacuum reading at idle. what fuel pressure?