318 low budget build

well are we working with what he has or what we wish he had?

I'm not too sure about that demon carb...with your engine combO I'd like to see a vac sec 600 holley.
the idea of using the rpm intake is good.

If you wanna go fast....forget about wether it idles rough or not.

BTW certain changes/things will help this and other things that you think would, won't.

we can tune around the 'less ideal' pieces in this combo.

In the realm of the '360 head department' the performer intake and it's smaller runners will keep the a/f better suspended in the lower rpm range, though it's not the best manifold, it may be for this.
The demon carb...ha ha well they say/advertise that they mix the fuel better/smoother venturis..yadda yadda, but if it was mixed better, you'd use less fuel right? demons use larger jets...and some comparative cfm ratings 'like the 750speed demon' actually have larger venturis than a comparative holley 750, That is garbage....
Barry grant is selling his name, not a superior carburetor...jmo

next, what ignition do you have?
and have played with the curve?
how much total and initial timing are you running?

what's the cranking cylinder pressure?

let us know