MARINER 115 low RPMs

Mariner 115, 1989 - S/N 0B131304 Starts fine and runs up to 2,800 RPM. Starts missing at that point. New plugs, rebuilt fuel pump, new hose and bubble pump, new gas - no impact. Checked coils with volt meter. Only 1 of 6 coils in specs at 300-1,000 RPM and it was not stable. Voltage ran continually fluctuated at 1300 to 1900 (digital) when should have been at 150-250 on 600 scale. Stopped test at that point. Been problem for a number of years. Sometimes boat runs up to 5,000 RPM. Other times on same trip, 3,000 RPM MAX. No pattern. Some times when cold takes 15 min to plane out. Other times, planes out immediately. Each time stopped is a different adventure. Never know if will work fine or will MAX out at 2800 RPM. Carbs rebuily a few years ago to address this problem. Ran a little better but did not solve problem. Acts like has a governor on it at times that prevents opening up. Have Mariner Outboard Service Manual 90-86134-4. Just has enough info to get in trouble because it covers too many models.
1) Any suggestions on problem?
2) Any better manual out there for auto engine guy who needs guide on Mariner?
This is in-line 6 - no distributor - 3 carb electric choke. If choke, bogs down more. Bubble works fine (new) holds prime - trying to pump more - no effect.