Horrible MPG/Fuel odor troubleshoot

Do those carburetors have power valves?

I see your point. I saw DP and jumped to conclusions.
I don't know anything about summit brand carbs, but they have to have some form of power enrichment, probably activated by falling manifold vacuum. I would imagine.
In that case, substitute power enrichment system for PV. It's only a little trickier, to tune.