I have the above engine on my boat. I bought the engine and controls from someone who started it (idling) on a hose. We shook hands, I paid him and got shafted.
The problem is; The engine starts and idles fine. As soon as you put it in gear and give it the throttle, the engine revs a little bit higher than idle, stays running, but barely holds 5 mph, a little more throttle and then it craps out. If you put it in neutral, it will start back up. It sounds like it is starving for fuel, but you can see the jets misting fuel and the butterflies opening.
UPDATE: While in gear and moving at 5 mph, I had a friend move the timing lever back toward the idle zone and it made no difference. The engine still stalls as soon at the butterflies start to open. The engine seems to be flooded when the plugs are examined after the stall.
Here is what has been checked and or changed: The Timing, the carburetors were cleaned but not adjusted, new fuel pump diaphragm, new fuel filter and all rubber hoses. New ignition module. The carbs are clean and shooting gas and both butterfly valves opening. If you open the throttle as far as you can with the engine in gear and running, and spray carb cleaner into one of the carbs, the engine stalls. This was an idea suggested from my local Merc dealer. The timing is set according to the procedure in my SELOC manual. All the settings seem to line up with the painted/unpainted factory points. The linkage works correctly.
Compression is good, all 4 plugs are new and have a hot spark. The spark is hot at stall-out. It was getting dark and I pulled one cylinder wire and connected it to an extra plug and grounded the case. Nice spark at all rpms. I have no tach.
Electric choke works and is not stuck. Tilt cutoff switch disconnected.
Irrelevant, but the battery is getting charged with 5.5 amps when it IS running.
Low end shifting is smooth and quiet. Clean oil in lower end and no leaks.
New water pump impeller and seals. New Shift lever seals. New Drive shaft seals.
I'm looking for that one tech out there that has fixed a million of these and
seen these symptoms.