Actually, you do want vacuum advance, to keep the valves, sparkplugs, and engine from overheating under part throttle load. It's all part of the combustion chamber design, and is specific to each engine. This engine was designed to have it. It is not just for fuel economy, it is for proper burn. Manifold vacuum is not appropriate for this engine design, either.
It would be a good idea for you to talk to Carbking about setting up the proper vacuum advance or swapping castings to get it.
