Not a JD Crawler Problem but, it Could Be

[Tractor 850]

I have a Ford model 850 tractor with a 172 CI gas engine.
The fuel shutoff valve was leaking around the stem so I replaced it.
Up to now the tractor was running fine.
Now it starves for fuel at high RPM's and under load.
If you are quick enough you can throttle back and catch it with the choke and keep it running. Very difficult to push snow this way!
If it does stall it starts right up using the choke. Before it would start with out the choke when warmed up.
Thinking I had a defective new valve I disconnected the fuel line from the carb and ran gas into a can. It ran a gallon in about 90 seconds running gravity through a 1/4" line. Ran the same test with the gas cap off, got the same flow so its not a vent problem.
This appeared adequate to me. Maybe its not?
Thinking I might have shook something loose I took the carb apart.
The carb is a Zenith Series 68 about 2 years old.
Nothing in the main jet or any passages. Carb still clean as new.
Checked the sediment bowl and screen at the carb, clean.
The screen on the new tank valve is still clean.
Thought maybe a vacuum leak, vacuum supposed to be 18" at idle according to the manual, was fluttering between 16" & 20" at idle.
Steady 16" to 18" a little off idle.
Tried spraying carb cleaner around the manifold with engine idling to check for vacuum leaks, couldn't get to all ports but found nothing.
Then I took the manifold off to check for cracks, nothing.
I put it back together today with new gaskets, problem still there.

I will order another new valve tomorrow and try that.

Any thoughts? Comments? Opinions? Wild guesses?

[Lavoy]

Just a wild guess, but been there at least twice on my own stuff. Is there anything floating in the tank that hits the outlet once you are running? You might not notice it sitting, but when you are moving, the gas is sloshing around.
Lavoy

[Tractor 850]

That's possible.
It dose do it while sitting still but vibration from the engine could move things around.
The tank was recently replaced. Replaced with a used one that had been professionally cleaned & pressure tested.
I have it off now to replace the tank valve again so it will be easy to check.

Thanks for the suggestion.

[digitup2]

We have had that several times on our smaller Deere crawlers that some foreign particle will cover the main line. Several years ago we had a crawler fuel tank receive several unneeded hands full of dirt in a mysterious way so I took a 12 volt electric fuel pump and hooked it up to pump diesel fuel and whatever out to a filtering system then feed back in and flush the bottom out of the tank .We now use this on every thing we can as it gets the dust and sediment that naturally finds it's way there and we can run it off a service truck right beside the crawler .And yes we got the guy he had dropped a parts receipt when his truck door was open from earlier that day It showed time of purchase and when they looked at the checkout video of that time He is now a fellow contractor but on a black list!! . Digitup.