If choking a little solves, or at least minimizes the problem, chances are that it's actually a lean problem- - - -but making sure the ignition is up to snuff is always "job one" before concentrating on the carburetor exclusively. One more test- - - -check the voltage coming to the coil from the ignition switch- - - -it should be within a small fraction of a volt as what can be measured at the battery posts with the engine running, unless there's a ballast resistor in the circuit. Once you're sure the ignition is doing its job properly, try raising the float level in the carb a little. It should almost, but not quite allow fuel to drip into the venturi at idle speed. As soon as the RPM rises to around 750-800 or so, you should be able to observe a mist of fuel coming from the venturi as the airflow increases above idle.
Jerry
