1755 Fuel Problem

I have a 1755 that I am having a power issue with.
As some background, we had the umbrella seal fail,
causing fuel to leak into the crankcase. We
pulled the pump off and had it rebuilt while it
was off as it had been a very long time. Upon
reinstall, rolled the seal, pulled again, put back
on, no power, found a restriction in an internal port. Tore pump back apart and retuned and reinstalled again and no leaks. But ever since reinstalling the pump the last time, we have had
intermittent power issues. The tractor will wind
up as it should, but occasionally it has no power,
no smoke, and loses rpms when under very light
load, same thing as before only not as often or as bad. If you drop the
throttle down and go right back up with it, it
usually will come right back out of it. It might
run for a half-hour without issue, then just show
up again. Over the weekend, I drove it an hour
and a half round trip to pick up an implement and
it did it at least 3 times.

Like I said, we pulled the pump because the seal
was leaking. I've changed the fuel filter,
checked the fuel line feeding to the pump with
great flow. Return can be easily blown through
with little effort.

We had the pump rebuilt both times by a guy with
30+ years experience. But, I'm almost to the
point to taking it off again and dropping another
$700+ into it to take it to a different very reputable
diesel shop.

Anyone have any ideas on what might be going on
here? I have no problems with other tractors
using the same fuel source either.

Thanks in advance.

If you think it might be the pump. I'd take it back to the same guy. He knows what he has done to it. I take it you have real good fuel flow to the pump.

Do one more test, with engine running, when it acts up and loses power and speed quickly loosten the two timing cover plate screws so fuel can leak out. If speed picks up OK this confirms a restriction on the RETURN line back to the tank. Old bits of the retainer ring, like coffee grounds can plug the line across the injector tops. Is worth a look. May also have something floating in the tank too.

We loosened the plate the first time we had trouble with no change in the performance. I can certainly try it again. It is my understanding that the ring was still intact when it was rebuilt initially. I have not taken the whole return system apart since it was easily blown through.

I considered something in the tank as well. I took the line off the tractor and ran probably 5 gallons of fuel out of it with no change in flow. That might not quite simulate the problem, but was the best I could do... I had no sludge come out of the water trap at this time.

How about the transfer pump? If it has a lead or is weak then that would starve the fuel supply.

Just a thought.
PaM

Last evening, I got the chance to try this test of loosening the screws again while the tractor was doing this. It made no difference in the performance.

I was able to replicate the problem rather easily just by messing with the throttle. I still have good fuel flow, so it would appear that I have something happening inside the pump, right?