I just went through a #21 Marvel for a 3020. If you leave the accelerator pump parts alone its simple enough to clean. Just don't use compressed air on those parts as one has a check valve that can be damaged. That valve needs a special tool to set it. A Zenith carb was also used
The electric deal shuts off fuel to the load jet so it doesn't backfire when shut off hot. If you want chest pain, price that out at a dealer! They do have a regular jet replacement now too.
Tim