Allis 6080 fuel issues

I have a 6080 we use to bale with, while using it this year it started idling higher and lower on its on and eventually dying. It wouldn’t start for a couple hours then once it did it would only run for a few minutes. Got it home and pulled the return fitting off and there was no junk or anything in it. Went ahead and ran a hose from the injector pump into a separate tank to rule out crud floating in the tank. It would just do the same thing. Hard to start and once it starts it’ll only run for about 5 minutes. The injector pump was rebuilt in 2020 at Cordell’s in Oklahoma. Any ideas would be welcomed

Thanks for the help. Blew the line out and the tractor seemed to start easier. It ran about 10 minutes before spitting and sputtering before dying again. That’s the longest it’s ran so far. I took the return line off and ran a clear hose into an empty bucket just in case that line was just plugging back off. It started right up again and did the same thing. Ran about 10 minutes and started sputtering erratically before dying.

That’s where I’m at with it also. Was just picking some brains that know a little more than I do. I’m a welder and not a diesel mechanic haha.

you need to take the actual return fitting regulator out of top of pump, it's the 1/8" pipe thread hex piece that screws right into the pump top cover. That check ball is likely plugging up, or somewhere down the line is plugging up between there and the tank. Possibly left over debris from the last failure? The aftermarket kit flex rings seem to only last a year or 2 as well. Most of the big shops like to build in their future work lol! Ope! it's out of warranty. Hope not. 

Yep, sometimes it’s the simple things! Had some black tar looking crud in the valve on the bottom of the tank. Thanks for all the help guys! Tractor ran good for around 2 hours last night. Pumped the tank out and now it’s getting a good cleaning!