Only realistic way to check/clean carbs is to tear them down, clean (careful w the jets), and reassemble.
Re fuel pump
. Sometimes the diaphram gets perforated and can cause issues other than work/not work. That's inexpensive and easy to replace.
Maybe a vaccum leak. They can be intermittent and only occur after sufficient vaccum has built up...like after a few minutes of running.
Tank vent. On the outside chance that you have an obstruction there check/clean. You can also make a run with tank cap loose to confirm vaccum is not forming in tank.
Another thought along these lines: is it a portable tank or permanent install? If perm, is vent on cap or seperate vent line?
If you don't get off that easy then:
Clean the carbs.
Inspect the fuel pump (esp diaphram).
Check all fitings on vaccum side of fuel line from pump to tank.