Outdoor Power Equipment and Small Engines - Older MTD roto tiller

Well its that time of year when I need my BORROWED tiller to run for 1/2 an hour or so.... but looks like I am going to have to invest several hours tearing apart the carb, cleaning , putting everything back together again .. then crossing my fingers and hopfully pulling on the starting cord.
This is an older 5 HP Briggs. ,metal gas tank , carb mounted with 3 screws on top of the tank ,with 2 plastic tubes protruding into the gas tank with screens on the end of them.There does not seem to be a primer bulb, there seems to be a breather tube off the side of the carb leading into the crank case.
The motor will start BUT only run if I drizzle a little gas into the carb with the air filter removed. But dies out a few seconds after i stop suppling fuel.

I would appreciate any insight into how this carb setup works .

PS-- this thing has started 1 st pull for years ?

I'd reccomend pulling the carb off and soaking it in a bath type carb cleaner, replace the pump diaphragm on the side, and the carb to tank gasket. Clean out the tank, and replace if the bowl in the tank is rusted enough that it won't hold fuel. Clean both tubes out. The long one pulls fuel from the tank to the bowl in the tank, and the short one is where the engine draws fuel through the venturi from.