Fast idle is controlled by an arc-shaped bit in the choke housing that has steps in it. The fast idle screw sits on the steps, sets how much the choke plates stay open. The fast idle screw is only accessible through a port in the choke housing. Getting it all right is enough to make you want fuel injection, which you'll never understand, and cast it all to a pro. (At least that's how I've felt about it).
Geez you got a lotta crud (technical term, ya know) in the float bowls. Really need an effective filter, Mr. Chris. I assume you have the filter on the gas line inlet? A lotta stuff can get through that metal mesh, but IDK if it's still coarse enough to obstruct a jet.