He said he had dirt in the carbs. Where did the dirt come from? I would be looking at some crap floating in the fuel tank blocking the pickup line.
Had a similar issue on a big loader one time. I know, not an apples to apples, but the result is the same. Crap was floating in the fuel tank and it would run great some times and other times it wouldn't run right at all. Finally had to take the fuel tank off, clean it out and all was well. Just my 2 cents.
filters don't stop everything.
If you have the right filter on it, if it passes threw
it it will pass threw the smallest fuel orifice
EDIT
when we added a charcoal filter we had a issue with
it when it would purge the charcoal filter.. it would
suck in charcoal and plug a air bleed.. we had to put
a filter on it... but this 70 he is playing with didnt
have the charcoal filter
