From what I have been able to find out,the way to check a Tecumseh carb is to shake it and listen for the rattle noise.You do this with the float removed,and holding the throttle and choke levers.The check valve is a small metal rod or emulsion tube.Any way the vinegar did work a little to clean up the powdery oxidation.I also soaked the carb in carb cleaner and used an old tooth brush.I'm waiting for some new floats to come the old ones have pin holes in them and one was full of gas.I still haven't tried to remove the Welsh plug in the side of the carb,there is supposed to be 3 holes under there that can be cleaned out.One trick that I have used is to rev the engine and close the choke and open the throttle wide open to suck out the passages in the carb.This works on older cars too.
A Briggs straight type carb also has a check ball in the longer of the two tubes, the one that goes to the bottom of the tank. They too get frozen solid from gas varnish and corrosion from water. I have used caustic soda [lye] to soak the tube. That works. The tube is brass and no damade is quickly done. The body of the carb should never be put in lye/water solution. It will go away real fast and produce hydrogen gas. A couple of times I took off the little brass screen on the bottom of the brass tube. This makes the check ball accessable. But it's necessary to put the screen back on by solder. Another way that worked was to use liquid soldering flux [acid type] and a small flame on a propane torch to heat up [gently] the tube in the check ball area. The crap fairly boils out so that carb cleaner can be used to clean it up.
