HELP...Broken Manifold Stud!

That's why. You didn't put a whole bunch in the carb. Remember when I recommended the 1/2 can in the valve cover? That's where you need it the most, I believe. To get rid of that sludge forming in the top of your engine. Next oil change, you can do it again, but go 1/2 in the carb and 1/2 in the valve cover. By the NEXT oil change after that, the inside of that engine oughtta be pretty clean.