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The Hitachi carb is a junk design that uses a solid brass piston on accelerator pump plunger, which pumps up & down in an aluminum bore! Over time the bore wears far out of tolerance and pump piston isn't pumping fuel anymore. The result is just what you have been describing.
Here's some general info, also posted for the next guy that comes along doing a search on fuel problems:
For any carb fuel system: Fuel tank, fuel pump, fuel filter, carb inlet needle valve, float level controlling inlet valve, main jet[s], secondary jet[s], metering orifices, air bleeds, shooter/cluster.
Possible failures are fuel pump, clogged filter, leaking/sticking inlet valve, incorrect float adjustment, restricted main or secondary jets, dirty air bleeds, clogged shooter/cluster, bad gaskets, casting or sealing defects, vacuum leaks at carburetor or manifold or tubing.
In some cases with electric fuel pump the fuel is pumped to carb but there's a restriction somewhere in the line, cutting down volume of flow.When starting the vehicle the key is turned on which pressurizes fuel line from pumping. The engine then starts when starter is used and runs for a bit, then dies. Remember, during this time after it dies while your brain is slowly reacting, the fuel pump is still pumping. Turn off the key, then turn it back on. Often we wait a second, then crank it again. That time before we shut it off, and the pause before cranking, may let the fuel pump squirt through just enough to partially refill float bowl to get it running again, but can't keep it running because of restriction.
Good to disconnect fuel line to carb and let it flow into a clean container, following normal safety precautions when dealing with flammable/explosive, and check fuel pump flow.
Most common cause of failure after starting, with engine dying, is a fuel restriction, pump failure or else low float level.
Many systems nowadays require a return line to tank, to finish the loop. With a restriction at return the carb ove- pressurizes and floods, or the fuel flow stops because excess can't return to tank, depends on carb design.
A weak fuel control solenoid can open just enough to dribble some fuel through but as electro magnetism fails at valve it closes back up, even if you hear a 'click' from it before starting. Take solenoid out of line, run direct fuel line, see if it fixes it. Bad electrical conections may cause the same.
The air bleeds act as a metering system, telling the system how much fuel to introduce into carb throat. When rebuilding it's always good to use a tiny piece of wire, maybe guitar string or similar, to gently swab out the air bleeds with carb cleaner. Don't ream oversize of course.
An apparent choking when stepping on throttle with engine warmed up, causing engine bog, can be the accelerator pump failing to enrich mixture to match increased airflow in carb throat.
Water in fuel can be puzzling. Adding a 'gas drier' which is mostly alchol should absorb the water. But it doesn't make it to fuel lines or carb. May be necessary to add gas drier, then pump through some contaminated fuel until treated fuel arrives, following flammables safety precautions. Suction contaminated fuel out of float bowl. Then return the contaminated fuel back to tank to be treated.
Using a rust remover in fuel tank can loosen rust and send it directly to filter, and even bypassing filter to clog carb jets. Clean system, discard fuel.
JimmieD
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