when adjusting carb be sure all electrical in in top condition before you start on fuel related items.
points, plugs, condenser, wires, dis cap, and timing. all must be right. be sure air filter is clean!!!!!!
also engine must be at normal operating temp, not cold. use regular gas, if possible, not ethanol crap grass gas.
try to find this posting
goggle Marvel-Schebler Carbureter
GROUP II, ENGINE
SECTION S, FUEL SYSTEM
I have it down loaded, but do not know how to copy it for you.
its a 23 page adobe fie on adjusting the MS carb.
be sure you know which carb you have, its should be on the side of the carb housing, you must know this as different carbs take different adjustments.
you know you have it when motor (warm) idles at 400 rpm's and you can take tractor out to the field or garden with disc on, drop disc into the ground and give the tractor fuel and it takes the fuel and motor speed up with no hesitation.