[rotorwrench]

The idle circuit is just for idle rpm due to the placement of the ports very close to the throttle plates. As soon as the throttle opens off idle then the fuel is no longer drawn from that source as it transitions to the main flow ports in the venturi. The accelerator pump gives it enough fuel boost to keep up with the demand of the falling manifold pressure as the plates open up. There could be problems with the main circuit flow or the accelerator pump but as was mentioned previously, there has to be a constant supply from the float bowl to keep up with demand. The whole fuel supply system is involved with that demand for fuel so the pump pressure should be checked and the tank & lines need to be free to flow well. Venting of the tank and float bowl is also important as well as float bowl fuel level. If it has an automatic choke then it has to function as intended. There might be crap in the main jets or crud in the atomizer circuits. A clean carb is your cars best friend.

The ignition system in a stock Holley Load-O-Matic system is also involved with advancing the spark as the engine rpm increases. Any vacuum leaks in the carburetor/ignition system function can cause major problems in off idle function. A bad condenser will make spark erratic in all rpms including idle for the most part.

Always check the easiest thing first during the process of troubleshooting. The old teapots can be leakers so make sure the carb is in good condition. A fuel pump pressure gauge is good to have and a mityvac can test the advance mechanism in the distributor.