The ammeter is fully irrelevant to this problem. The truck starts, idles, revs but stalls when put in gear.
Question:
How does it stall?
Does it just bog down and die or is it more violent, which would give room for the suspicion
of a mechanical blockade in the transmission or converter? Does it stall when fully warmed up?
Did you check all vacuum canisters (there's one on the carb and one on the distributor aswell as the brake
booster (just a big vacuum canister)), all vacuum hoses and the carb itself for leaks?
If not, start here. Replace where necessary (canisters should at least HOLD 15 in/hg of vacuum for a period
of time (like 15-20 minutes minimum). Spraying brake cleaner around the carb base should not make the engine
rev up. If it does, there's a vacuum leak.
Don't check vacuum lines with your mouth, you wont make enough vacuum, use a vacuum pump
It's also possible that the venturi cluster tubes are clogged.
The venturi cluster sits down in the carbs throat, they can not be seen from there, you have to remove the
choke plate, then remove the two venturi cluster screws and remove the venturi cluster. You should have new
gaskets at hand. The venturi cluster breaks down in several parts, one has the thin brass tubes pressed into the
underside. Clean these with a very fine wire and compressed air. Make sure they blow through freely (could check
that with your mouth).
I've had carbs in my hands that wouldn't idle or run at all and their venturi tubes were fully clogged with residuals.
Check these things and return to this thread to tell us if that worked or not.
Alex