Bobcat 773 Rough Running After Engine Warm Up

[Dameon]

773 with about 2400 hours on it. Regular maintenance, not abused. Runs great when first started, but when the engine is fully warmed up (maybe 15-30 minutes runtime), it starts running rough. Within the next 5-10 minutes it'll barely run at all and will usually just die. If you can get it started, it'll just die almost right away. If I go pump the fuel bulb, it starts fine and runs great again for a while, then starts the same behavior. If it's running rough and I pump the bulb while running, it clears right up and runs fine for a while.
This model has the Kubota 56hp turbo diesel engine, V2003EB-T. As far as I can tell, without really digging into the engine bay, it has a mechanical fuel pump. Judging by the parts schematic, there are no other lift pumps (in-tank, in-line). It would make sense that the fuel pump might break down when heat soaked and goes back to normal when cooled down. A replacement fuel pump from the Bobcat place is $95. Not outrageous, but if there is a chance it could be something else, I don't want to waste $95.
Suggestions appreciated. Could it be a vaper lock issue? Maybe a crack in a hose that's letting air in? But why only when warmed up?

 

[OldMachinist]

Sounds like a clogged fuel cap vent. Try running it with the cap loose to see if the problem goes away.

 

[Dameon]

Sounds like a clogged fuel cap vent. Try running it with the cap loose to see if the problem goes away.

That's an interesting thought OM. I did recently replace the old cap with a new OEM unit from the Bobcat place. Maybe a defective cap? I assume you are referring to the fuel filler cap?
Thanks.

 

[OldMachinist]

That's an interesting thought OM. I did recently replace the old cap with a new OEM unit from the Bobcat place. Maybe a defective cap? I assume you are referring to the fuel filler cap?
Thanks.

If you still have the old try putting it back on for a while.

 

[Dameon]

If you still have the old try putting it back on for a while.

Unfortunately it's gone. I'll just run around without a cap. Maybe put a piece of screen or something over the filler hole "just in case".

 

[Bobcatdan]

Unfortunately it's gone. I'll just run around without a cap. Maybe put a piece of screen or something over the filler hole "just in case".

Replace the fuel filter, that is probably the problem. The fuel pump next to never fail and if they do, they just do.

 

[Dameon]

Replace the fuel filter, that is probably the problem. The fuel pump next to never fail and if they do, they just do.

I intended to replace the fuel filter, but I couldn't find a way to correlate the issue to be a filter issue. It's too consistent with engine warm up timing and pumping the bulb, which is utilizing the filter of course, consistently, but temporarily, resolves the issue.
I'll go ahead and replace it after removing my cap. One change at a time.
Thanks.

 

[Bobcatdan]

I intended to replace the fuel filter, but I couldn't find a way to correlate the issue to be a filter issue. It's too consistent with engine warm up timing and pumping the bulb, which is utilizing the filter of course, consistently, but temporarily, resolves the issue.
I'll go ahead and replace it after removing my cap. One change at a time.
Thanks.

A fuel filter will resolve 98% of all running problems. Fuel caps not venting were an issue for a while, but looking back, I think it was a bad batch because I have not seen it in years.

 

[Dameon]

A fuel filter will resolve 98% of all running problems. Fuel caps not venting were an issue for a while, but looking back, I think it was a bad batch because I have not seen it in years.

As I intended, and as Bobcatdan suggested, I replaced the fuel filter. I removed the water drain from the bottom of the filter and water poured out. Apparently the drain hole was clogged. I removed the filter and dumped the fuel into a glass container (like I always do) and didn't see any water or debris. Put the new filter on, opened the top bleeder, pumped until I had fuel coming out the bleeder, and started it up. Sputtered a bit and then ran cleaner and smoother than ever. In fact, I thought the engine had an RPM govenor at about 2500 as that's all it's really ever been able to do, but it fired smoothly up to 3100 or so. I usually run it around 1900-2000 when working, so I never thought about it.
So, the filter appears to have been the problem. Lesson learned. Do the obvious stuff first before bothering the forum. Maybe someone less experienced in engines will find my thread and save themselves some time.
Thanks all.