Have a new Gravely (50 hours) with a 25 HP Kawasaki. After about twenty or thirty minutes of mowing it stalls. Before that happens, it runs fine. Can start it back up using the choke, then runs five minutes and stalls again. Just replaced the In-Line filter and same thing. I am suspecting the fuel pump because when I disconnected it from the vacuum line...I smelled gas in that port of the pump. Looks like I am not the only guy with the same problem on this issue. Any suggestions?

Anti afterfire (carb fuel) solenoid is suspect. If it has a removable plunger take it out to test if problem goes away. Else snip off the plunger with a pair of side cutters.

The only caveat with this test method is if the magneto kill circuit is not functional you'll need to choke out the air intake or pull the spark plug wires to stop engine.

If you're using a neon lamp type spark tester directly to chassis or engine block then, yes they can light with current that is insufficient to effect sufficient spark. Try connecting in series with the plug or use a gap type tester or the actual plug.

The Kawasaki v-twin uses two separate ignition modules (magnetos with electronics) and although not impossible it is unlikely both would fail at the same time or one would fail and stop the other from working.

It is more likely a safety circuit is causing the no run state. For this model, locate the RUN relay and check that the WHT/BLK wire (magneto kill) is open circuit to ground (engine block). If there's continuity to ground then magnetos are killed. Ignition switch OFF or PTO switch ON and seat not occupied are other kill states.

See parts diagrams for schematic.

https://www.gravely.com/en-us/partsdiagrams?search=991128

When it stalls out did you check the spark? I suspect the engine is losing spark due to an ignition system failure.

Check the torque on the head bolts. I can't tell you what it is, been a long time. If they are good, run it till it dies. Then check for spark at the plugs or coil/s. No spark replace the coil/s. My guess would be coils. But I have seen the head loosen up.

Check the breather in the filler cap. slaken it off when it starts to die, if it picks up again replace the cap.

Have your fuel pump checked. The wires on mine were melting due to the regulator attached the pump being bad so when the mule would first start it would run fine until it warmed up and then no gas once the wires warmed up. Don't buy the Kawasaki replacement unless you want to pay $300 or more for the part (They are crazy over-priced on parts) and labor. Got a 3rd party pump for $50 and had it replaced for one hours labor and we are good to go. Worse case next time around I buy another $50 pump and replace it myself

do you have dirt floating around in the carb?

This may or may not have anything to do with it however I have the same engine on my Cub Cadet Enforcer and what I found to be the problem was a wire to the saftey switch under the seat had broken. This made it sound like an engine problem by making and breaking contact as I was mowing. My first thought was a fuel filter stopped up as it was sounding like it wasn't getting fuel because it was OK when I was stopped and the engine wasn't loaded.

Check your Vacuum line going into the back of your air intake box.

try checking your cadlist convert on your exhusted