Mercury Classic 50 rpm problems

I recently purchased a boat with a 1989Mercury Classic 50. Upon reading a number of reports of the autoblendfailing, I removed the autoblend unit and chose to mix the fuelmyself. I took the boat out for the first time and found that themotor would not go above 4000 rpm at WOT while in gear. While out ofgear it will reach a higher rpm and idles fine. The previous ownergave me paper work showing that in 2007 the motor was given a newstator, switchbox and the carbs were rebuilt. I was wondering if I may have caused a problem by removing the autoblend or maybe it needa new fuel pump. Any thoughts on what may be causing the motorsinability to reach a higher rpm while under load would beappreciated.

A number of things that you need to check. First thing , is the propeller too big ( too much pitch ) for the boat.--------Removing the autoblend was a good move , and is not a cause of low RPM.-----------I would check compression to make sure motor is in good shape internally too.------------Motors will rev up just fine in nuetral running on 3 of 4 cylinders so that realy proved nothing.--Try operating the manual fuel pump while at 4000 RPM on the water to see if that helps.-------Could be as simple as a bad sparkplug too !