in order for fuel to get out, air has to get into the tank.
Because it is after the mower deck that air will be dusty.
Add to that the odd blade of grass ( which goes translucent in fuel but does not break down ) and you the receipe for a nice fuel plug.
Generally it will manifest itself as running fine for a set period of time , say 1 hour then starving and refusing to run till the next day when it dutifully runs for around the same time then goes into an encore performance.
A quick shot of compressed air up the fuel line every now & then should see you through the season ( fuel cap off naturally ) when you can pull the tank & clean it properly.
We had a spate of 2000 series Cubs doing this and all of them had a moulding fin inside the tank outlet a few minutes with a scalpel and they were as right as rain and some of these had very long service records for random stopping.
Way way back we had a poster who photographed what came out of hi tank, pliers , a glove, some bailing wire, a couple of old cap vents , sticks & stones really amazing.
