When was the last time you cleaned out the fuel tank ?
You get floating debris in there that gets sucked into the outlet tube, not enough to totally block off the fuel flow all together nut enough to slow it down so it can not keep up with the engine.
Also the air inlet can get blocked.
This could be a vent in the cap or a tube with a charcoal filter on it.
So start by running will the cap loose.
Problem goes away then it is venting
No joy, remove cap and fuel line at the first joiner ( filter usually and blow some compressed air back up the line.
Mows for a lot longer means there is debris in the tank.
After 1000 hours both of these could be happening.