Stuart,
I guess its the Rochester 'B' they put on those 230s. Anyway, yeah, that weird plug thing they stuck inside the carb body. I've never had a problem with mine, but watched a guy tear his hair out over a few days working on an old Caterpillar. Finally found out there's a similiar filter in his deisel pump, and it was clogged.
Speaking of deisel pumps, shmkr, my tractor was acting similiar to your truck last month. Run five minutes, quit. Run an hour, quit. Run fifteen .... All the diagnostic stuff I did indicated no problems. Changed the filters, it acted the same. Brought the injectors and the pump to the shop that rebuilt them last year - everything checked out. Stuck in the middle of the field, again, I said: This is rediculous. I tore the entire fuel system apart right there in the field, cleaned everything, extra clean, changed filters, again, bled and rebled the lines, used fresh deisel, and ... started right up and haven't had a problem since. I know this isn't the hard, concrete advice you seek, but that's the way these problems go away sometimes. Take it apart, put it back together.
Also, I like Neilroy's see through filter idea. I run those on both my trucks. Don't know why - I just like to keep an eye on things.
