Outdoor Power Equipment and Small Engines - Sooty Briggs Vanguard

I have a new color scheme on my Simplicity tractor--factory orange covered with a layer of jet black soot. The engine is a B & S 16 HP Vanguard twin, model 303777, Type 1111-A1, code 96112011. It starts and runs fine but certainly appears to be running rich. The foam and paper air filters were replaced in May this year and seem fine. I checked the choke plate and associated linkages and everything seems fine there. I didn't run the engine without the air filter to verify the (manual) choke comes off but I'm pretty certain it does. I did remove some oily dirt/crud from the bottom of the carburetor throat and thought this might fix the problem but it just lessened the problem. This problem developed rather suddenly. It literally obscured the orange paint on the hood and front of the mower deck, and coated my left shoe and pant leg. What else should I check? The engine hour meter shows about 250 hours (I bought this second hand a few years ago so can't vouch for the correctness of that reading).

while i am not familiar with that engine.
an over rich condition/possible trash in fuel causing the needle & seat -not to close,causing a high fuel level.while you are in there-make sure the float it self is not full of fuel(wont float)

I agree with the needle/trash diagnosis. First try running it without the air filter and also verify that the choke is in fact opening.

OK, so I removed the air filter and watched the choke plate as I shut off the choke--the choke plate moves to the open position (parallel to incoming air) as it should. I was going to take off the carb but it looks to be a bit of job and I didn't have the time. I checked the fuel filter: I have one and it looks pretty clean. How could I get stuff in the carb bowl if the filter is there? I could understand how a cracked and leaky float could occur but how can particulate contamination get past the fuel filter?

I don't know what filter you have but if it's the "pancake" type,, inside is just a screen,,,Lots of little stuff can sneak thru them.. If you have an automotive type filter than any part of the fuel line that comes apart from rotton fuel lines (Very common) after it will wind up in the carb... Roger