I understand that worn bushings on the throttle shaft causes this leaking. This is a typical issue with well-used rochester carbs I think.
The worn bushings cause them to leak gas and also to suck in air. I've been told that the local lawn mower or electric motor suppy stores have suitable bushings. You need bushings that will fit your throttle shaft and that are a little larger then the shaft holes in the bottom carburetor plate. Then you have to take these parts to a local machine shop to fix the carb.
I haven't done this, but my original Rochester carb leaks here, and I'd like to repair it. The rochester carb works fine on my 235 - notwithstanding the detractors out there.
I have a HTML detailing this repair with pictures. It's for a different carb, but I bet this job is generic. If anyone thinks it helpful - I'll post the HTML on my server.
I'd like to hear from others who have done this repair - it would be really useful to a lot of us.
