Carburetor trouble

Description sounds like vapor lock. If it is, it may be occuring on the suction side and that's why the pressure drops and then burps up. You smell fuel because its coming of the carb as all vapor instead of mostly a dispersed liquid. At moderate throttle the engine acts something like a combo of its too lean for the load and running out of fuel.

Go over the entire fuel line. Look for any possible pin hole leaks on the supply side to the pump. Look for all locations that may transfer heat from exhaust and headers etc. Insulate as needed.

I've added insulated firesleeve and then covered that with reflective type insulations since having a problem last April. I'd run the car the previous summer no problems at all. So sometimes all that's needed is summer fuel. I just preferred to take the extra precautions against very warm days in the Spring.

This is the worst time of year for using pump fuel. Temperatures are often into 70s and 80s but we're still using winter fuel. Winter fuels are allowed much higher Reid Vapor Pressures (RVP). This helps cold weather starting, and is also cheaper to manufacturer. In our favor, every retail outlet must be be selling 100% summer fuel by June 1. Refiners and distributors must be supplying it by May 1. A few states also have fuel drivability requirements, and others have lower RVPs than the US EPA allows. So not all fuel across the US and Canada is the same.