briggs and straton vtwin single barrel carburetor

my engine is surging so I pulled of the carburetor and found something that im not sure what it is. may be build up from old gas or deteriorated plastic. also it looks like something may be missing from between the jet and the tube it sits on. I was hoping get some in put on this and maybe what manufacture it is. the engine is a 21hp vtwin intek. I am probably stopping at a mower shop tomorrow.

Not familiar with that carb but sounds like the idle circuit is running lean or clogged. The pulsing is the governor reving the engine to keep it running on the main jets. Do you have an idle mixture screw, if so, turn it out till it smooths out. If turning it out doesn't do anything after 6 whole turns from all the way in, then the circuit or pathways are clogged.

General diagnosis of the problem I use to figure where to look. Can't tell you which little pathway to look at to see if it's ok or not ok.

yes it was running lean the plugs where burning white. I learned to follow the freeze plug to the corresponding holes and clean those. I didn't soak it yet because my chem dip is old and it all evaporated. really I would like to find a older adjustable carburetor and throw away this nikki but not sure what to look for. I have the numbers off the carburetor but cant find them on the internet I found different numbers.

Cool, Good job. Unless you are planning on modding the engine, it would be a good idea to just keep that carb. You already have a good idea on how to fix it, why spend the money.