When you step on the throttle, the engine seems to bog down and in some cases die.
A bad distributor advance can cause a hesitation when stepping on the gas, but we aren’t addressing that here.
Stepping on the throttle is where the accelerator pump circuit comes into play. When the pump moves up (let up on throttle), the accelerator pump well is filled with fuel. Some get the fuel by filling over the top of the well through a slot on the side, others use a intake at the bottom of the well which is shut off with a check ball.
In most 2 jets the small aluminum check ball goes in the pump well. In a few 2 jets the large aluminum check ball goes in the pump well. At any rate aluminum is used because it is light and easy for the fuel to lift up.
With the engine off, pump the throttle while looking down the carburetor throat. You should see 2 strong squirts coming out of the venturi. If not, then you have a blockage somewhere.
The small holes in the venturi can be blocked with ethanol residue. run thin wire down the holes.
Check the gasket under the venturi, they don’t always fit well and have to be trimmed. If they are too big then the venturi won’t site flat.
Put fluid in the pump well and press the accelerator pump down. Fluid should come out of the main discharge.
The main discharge should have a check ball, spring, then a T to hold it all in. This is where the bigger stainless steel check ball resides.
Blow air through the passage way at the bottom of the accelerator pump well. Air should come out of the main discharge.
Is your accelerator pump cup getting stuck in the well? Most wells are tapered so that the pump gets tighter as it goes down. If ethanol has damaged the pump cup then the cup may be swollen.
Does your accelerator pump have a delayer spring (spring over the stem) and on non marine a return spring below it?