[911pcars]

First, I'd make sure the float isn't hanging up on the side of the float chamber and the pivot pin isn't bent.

Anything else blocking the fuel inlet? Existing Weber screen filter still there?

Next, I'd try Grose Jets, a ball-type inlet valve that replaces the needle and seat type valve. I'm pretty sure they still sell them. Supposedly, they have better (more positive) shut off characteristics. Although you have more than enough positive shut off, maybe these would help.

Hope this helps,
Sherwood