what causes a 89 b2200 carberator to fill slowly

Bad pump, bad float, clogged filter, clogged line, and maybe something that I failed to mention. Carb fills then runs dry because the fuel needed to run the vehicle is more than what's entering the bowl.

Nothing like taking a picture in the bathroom mirror. I'm surprised that your 1990 is carbureted.

Could also be (besides what John already stated,) dirt/rust in the tank causing the fuel sock on the fuel pick up to clog. These are usually made of a fine plastic mesh. Or varnish if the vehicle sat for a long time with old fuel in the tank. It could be mis-adjusted float as well, not opening fully when it needs to be.