Bobcat 743 power issue

A year ago I noticed that my 743 (natural aspirated diesel) Would choke out after about an hour of hard work. I sounded like it was starving for fuel, so I put a new mechanical fuel pump in it and thought the problem was solved. I only used it for short jobs and not at full throttle until now. The symptoms now are:
Pointing up hill it runs good
When I point downhill it seems to lose 350-500 RPM
Pointing downhill it will eventually choke out. It feels like it is starving for fuel, but the exhaust is black smoke, like I am over fueling it.
Once it chokes out and dies, I wait for 5 minutes and restart it. If I have to continue pointing down hill, it may stall 3-4 more times. If I can swing it around and and point it uphill, it takes about 2 minutes to "clear up", then the RPMs and power come back.
A mechanical oil pressure gauge shows 40 psi at elevated RPMs, but at idle it shows 20 psi. 20 is just above the RED zone and the GREEN zone starts at 40 psi. It is in the white zone 95% of the time.

The hours meter shows 550 hours and has always worked since I got the machine. The former owners used it to clean 2 horse stalls twice a month, so I kinda believe the meter.

Where do I look?? Air and fuel filters have about 30 hours on them.

Which engine? The 743's Ive been around had the 1702(maybe 1402?) Kubota. Does it still have the primer bulb in the fuel line?

Yes, primer bulb. I don't recall the engine maker, just that it is a naturally aspirated diesel

Fuel pickup pipe in the tank in good shape?

grandpa said:

Fuel pickup pipe in the tank in good shape?

Click to expand...

At the age of that machine, no. It needs to be replcaced, along with a new check valve.
Not a matter of "if", just when it will snap off.

Ed

OK, I'll replace the pick up tube. Any surprises in going this job??

Actually............no. Raise cab, remove the fuel line and pull the tank unit.

Ed

OK, it will be one of my winter projects

Seroiusly, it's a 45 minute max project. Do it now while the machine runs and you can do the job where you want to.
When it fails, it'll be someplace that makes it a miserable job.

Ed

It's autumn. I have firewood to get in, 2 antelope tags, an extra deer tag and a Cat 955H that I just replaced the turbo on and need to get ready for snow removal. All that, plus the 3000 miles a week that provides income for my household. I'm not a mechanic and can think of NO JOB that is only 45 minutes on a machine. I'll chance it for the next 10 hours of use over the next 2 months. By mid Nov my tags should be filled, 3 cords of wood stacked, then I'll have time to do this job.

By tank unit - are you saying I pull the fuel tank out??

NO. It's right out in the open when you lift the cab.

Ed