M51 multifuel lack of power

Trying to get my old multifuel up and running. My problem is it’s lacking power. I can’t get past 3rd gear. Go to 4th and it just lugs and won’t rev. When not moving and you try to rev it goes to 1000 pretty quick, kind of slowly revs till it hits 2000 then does pretty good. About the same when driving it. Changed all the filters and a bunch of other maintenance. I’ve had to turn up the fuel screw quite a bit to get it to start and idle which it does great at now. I’ve turned the droop screw up and down but doesn’t seem to effect it and going higher with the main screw doesn’t seem to be making a difference. It does build boost, about 12psi. I haven’t got to monitor the egt gauge yet. I had to install a new one. It puffs a decent amount of black smoke. I pressure tested the injectors, some kinda leaked so I sonic cleaned em, reset pressures and reinstalled. I’ve set the valves. I’m down to saying screw it and install a new ip and injectors. Any ideas before I spend a bunch of money?

How long did the truck sit? Black smoke equals unburned fuel and equals high exhaust gas temps. My best guess is your are experiencing no timing advance from the governor assembly. Some good reading. https://www.steelsoldiers.com/showthread.php?58845-M35a2-Timing

It sat for Atleast a year. There was a lot of fuel in the oil too. I was hoping when I drove it it’d clear up the smoke and fix the lack of power but didn’t.

If it had a lot of diesel in the oil, I'd get ready to bypass the Fuel Density Compensator and replace the o-rings on the Hydraulic Head if it is a known good pump. It actually might be time to pull it and find a competent shop to go through it and freshen it up a bit. A word of advice, don't drive it much if you haven't changed the engine oil. If you decide to pull the injection pump and have it rebuilt you may have some trouble finding someone who will even consider the job. If you run into trouble finding a local shop that will handle the task, send me a message and I'll steer you towards a local shop in my area that still works on this old stuff. I had to get the injection pump rebuilt on my 5 ton NHC-250 and only found 2 shops within a 100 mile radius that would mess with it.

The fdc is bypassed and I have changed the oil. It’s got a small fuel leak around the hh but seems to be coming from where the lines go in but they’re tight. I’ll probably just order a reman from one of the vendors vs having it rebuilt locally