Most likely a blocked up fuel screen, or the fuel bowl in the tank has water or rubbish in it.
There are briggs workshop manuals but most are printed, I've not seen them online.
That little spring doesn't do much, just takes the slop out of the throttle linkage. you're local mower shop should have one but last time i got one last week it was approx $15 for it
3 bolts remove the carb, 2 head bolts and one at the back of the tank.
Carb off, remove the 3 i think screws that hold it to the tank, check the tubes that go down into the tank. they have screens in them. Won't hurt to check you're diaphragm while you have it off too.
