How bad is your hunting? Can you see an actual change on your tach? I sometimes get a hunt (same motor) but it's barely noticeable and can be eliminated by changing rpms just a smidge. I think sometimes sympathetic vibrations can be mistaken for the engine hunting. Have you checked your coupling alignment lately? Prop for dings? Cutlass? I run at 26-2800 rpm and feel 3k constantly is a bit high but a lot depends in the individual set-up.
"Hunting" usually refers to cycling rpm up and down. If you are just dropping rpms, that's a lot different. Can you make it regain rpm by throttling up? Maybe just linkage? If you can't get it above 2gs, there's something wrong with the engine itself, probably a fuel blockage or air leak. Did you check all the bleeders? There is one behind the rubber water line by the injector pump. Make sure all the banjo fittings are tight, fuel filter cup is seated well, filters are clean. Air leaks can be insidious problems to find. Is your tank clean? If it has a screen on the end of the dip tube, losing rpms from fot clogging it is a classic symptom.
Yes, am losing rpm's....after running at 3,000 drops to 1500 then rises again and repeats...only happens after running for about an hour.....all the other issues you've mentioned have been attended to...more then once...it's driving me crazy plus missing out on fabulous boating weather !!
I've had two instances of similar problems. The first one drove me nuts. There was a hairline crack in the crappy plastic dip tube elbow that goes into the fuel tank. It's not in a spot where it's easy to see and the crack was almost invisible. I wrapped the entire thing with epoxy and fg cloth neatly and it's better than new. The second instance was from fot in the fuel tank. The fill tubes on some tanks have a screen over the end at the bottom of the tank. It clogs easily. I took the fill tube out and poked much larger holes in the screen. Some people recommend taking the screen off altogether. Your regular filters catch dirt where it's easy to remove. Taking the dip tube out also let me siphon out any remaining contamination. Your problem sounds VERY much like this second one because the engine does not die, it just loses rpm. Hope this helps. These things are like a puzzle
Maybe do a process of elimination next. Run the engine directly from a clean tank. Use an outboard tank if you have one. Just run a piece of tubing from a container to the fuel pump , bypassing tank, fuel line and any filter. If the problem goes away then you know you have an air leak somewhere from tank to engine. If it still happens, you've eliminated the tank and fuel lines as culprits and can focus on the engine.
One thing that was discovered in our engine rebuild process..the return line and the pick-up was swithched. Try taking off your pickup line and try blowing into it. Then try blowing into the pickup line. Two things should occur while blowing into the pickup line..you should here bubbles in the fuel tank and their shouldn't be alot of resistence.
Have had a couple of mystery intermittent fuel issues. One was caused by the rubber inner liner of the suction fuel line collapsing Replaced the line with good stuff. Another was caused by a bit of plastic bag or candy wrapper in the fuel tank of my car. Nasty,, abandoned the car in France. Once found a chunk of impeller rubber in the elbow inlet to a Racor .Can't even guess about that one.
Is your Morse control a single or dual handle(s)..one for throttle and the other for transmission(forward,neutral,reverse)..or integrated into one handle with a push button to disengage the transmission from the throttle??
Check the throttle cable as it may be backing off due to lessened resistance in the cable from heat and or vibration.