On the marvel carbs you have a plug in the bottom of the belly. Pull it out and drain the fuel in the carb. If no fuel drains you have debris in the the belly, poke something up in the hole to move the debris. Once it starts draining smoothly reinstall the plug.
Is your mag getting hot? How do your plug wires look?
There is a link on my engine drives page about the Marvel carb, Look at it.
Chris in Odessa, is a good guy and a welder mechanic. I haven't seen or talked to him since he left Pauls Valley.