Speaking of lift pumps, does your tractor have a hand primer pump? This is usually a knob that turns to loosen, then the spring pushes it up. You open a bleeder screw or crack a fuel line, unscrew the knob and then pump in and out with the plunger to purge any air trapped in the system. If you forget to push the plunger down and tighten the knob it can be a source for air being sucked into the system.
Here is a picture of my injection pump. The primer plunger is the gold colored cylinder above and to the right of the red circle. The bleeder screw is the screw with a ring through it up and to the left of the primer pump.
I don't know how a loose or leaking primer pump could be temperature sensitive but we haven't determined for sure if the temperature is the cause or just coincidental to to run time it takes for the problem to show itself.
If you don't have a lift pump or a primer pump all this doesn't matter.
A couple of questions:
Is the outlet of the fuel tank above or below the level of the filter/and or/injector pump.?
Does the engine have any changes to the exhaust, more or less smoke, just as it starts to die down?
Does it make any unusual noises as it starts to die down?
One would think that if it is fuel starvation it would sound just like backing the throttle down and there would be no smoke. But if for some reason it was "loading up" like with a dripping injector it would kind of "bog down" and probably be putting out some extra smoke. Bog down and die down are subjective terms and I am not sure I could tell the difference except for the exhaust output. I certainly couldn't describe it in writing.
Sure wish I could get my hands on this one, it is quite the mystery....
Oooh, excellent questions…the filtered fuel exits at the top of the filter housing (it enters at the top on other side). You think air may be intruding due to slight warpage of bowl? I did replace bowl and filter.
Unfortunately, no this 1920 does not have any sort of plunger as you’ve described, just a bleed screw which I used extensive today after changing the braided (filtered) fuel line.
Re exhaust color, if there is any change during this cycle it is imperceptible to me.
Re unusual noises, no. I turn the tractor on and just come inside now having tested so many new parts etc expecting it to keep going after about 20 min. I can hear from inside (and out there too) the RPMs cycle down by about 1,000 and the back up then it will drop (for example) from 2,000 to1,700 and continue as it struggles to maintain the RPSs initially set for the test. I have varied the engine speed and when it is initially set high it takes less time to enter the “death spiral” than it does when set initially at 1,500. This is the basis for my heat-oriented explanation, parenthetically. I did just buy an infrared laser thermometer suggested by another TBN user and am going to do some checking in pursuit of that as a possible source. Still, if it IS hear related it suggests a warped head or other dreadfully expensive problem!
Oh, btw this tractor is NOISY and has been since the day I bought it. Compared to my tc45da it sounds like a jetliner. I’ve put only 300 hours on it since I bought it 6 years ago. Changed the muffler to no avail. Conceded that it is an older tractor (1999) and the exhaust is at face level unlike the boomer which exhausts downward, lower than the operator’s ears.
Thanks again for you cogent set of inquiries,
Danica