Briggs chokematic carb--adjustments????

I have a Rally walk-behind rotary mower. It has a Briggs & Stratton 3.5 "Classic" engine with the "Chokematic" carburator. The engine runs very rich (almost stalling). I replaced the foam air filter, and cleaned the gunk off of the throttle springs and tried to make sure the throttle cable was not pushing too far into the choke/start mode... no luck so far...and it seems that this carb doesn't have any setting screws to adjust.

Questions:

--are there any adjustments on this carb?

--is there a fuel filter that needs to be changed?

--I'm wondering if the entire carb can be switched to the older kind with adjustments.

Briggs & Stratton's site was no help.

Thanks-in-advance for any advice

"choking on exhaust"
Connecticut