Duster running rich

A modified engine combo like yours will always run rich, and for good reason.
An engine that runs rich, just burns extra fuel.
An engine that runs lean, especially under load burns parts. eg pistons,valves etc...
Why a double pump carb for the street ?
To get the best possible A:F number. Find a shop that uses an exhaust gas analyser to tune with.
The biggest problem with home engine builds is that many parts tend to not compliment each other.
Think of 2 cooks each baking a cake.
One baker uses a tested recipe so he knows what to expect.
The other baker use similar ingredients but doesn't have a complete recipe.
Sometimes you need to back up and start over instead of tweeking a bad/unknown recipe.
And keep this in mind, " A good street engine/car generally makes a bad Race car, and vice versa ."
Street cars need to run well at various speeds and rpms for sometimes extended periods of time. The "race engine" runs at normally just high RPMs for a short period of time.

You need to decide what compromise you are willing to put up with. You can't have your cake and eat it on an old school type engine.


Modern, computer controlled cars can get crazy horsepower and decent gas mileage.
But that is because they are computer controlled with many sensors feeding info into a sophisticated computer that adjusts everything many times a second while you just control the go pedal.