Disconnect the fuel line at the carb and hold it a few inches below the tank. let the fuel siphon freely into a jar and measure the flow rate. I believe it should flow at a rate similar to what the engine demands at full throttle - probably around an ounce per minute. If the pumper portion of the carb is working, it should be able to deliver at least as much as this siphon test. So if the siphon test is OK, then I would think your felt clunk and fuel tubing are OK. The pump could be weak. In this case you replace the diaphragm of the pumper side of the carb. I had a similar issue and found that my tubing line from the regulator side of the carb into the fuselage was melted shut. completely closed off where it passed by the muffler. I was running a line from the atmospheric reference side of the regulator into the fuselage in order to minimize surging due to changing cowl pressure. Most carbs do not have this line.