well what are the compression numbers ??? if electricals are OK we can assume it is not sucking fuel properly to feed the cylinders
check all negative pressure points…
a- starting at the fuel pick-up (change tank and hose if neeed be )
b – divide to conquer…. feed the carb manually with a small fuel supply and hose to the carb inlet thus bypassing the, air pressure pulse , hoses and pressure tank as a problem source
if idling is ok work backwards . low pressure pulse feeding the tank (bad check valves behind the inlet manifold)
c- if still idling bad with a small fuel supply on the carb inlet …….. problem is on the engine side
d- possible loss of crankcase negative pressure causing a weak pull on the carb idle circuit fuel supply ( crankshaft bearings allowing external to be sucked in the crank case instead of fuel from the carb)
e– carb gasket not sealing , LS needle packing inadequate sealing,
f- check the throttle plate at the rear of the cab .. it should be pretty well closed at idle to have the fuel sucked out of the idle chamber
g- btw did you clean out the VERY small jet in the side fuel channel feeding the upper half of the carb ? (look closely inside the feeder
channel) clean it out with a VERY VERY small wire and flush with carb cleaner and air pressure blast
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