Andy's advice is exactly what I would have said for checking spark, cuz I do it that way often. One addition to that advice is to make sure the screwdriver blade isn't touching metal when you push the points open. Another self-taught bit of advice is to make sure your pointer finger hasn't slipped off the plastic screwdriver handle and is touching the metal shank of the screwdriver. Doesn't shock you real bad but it wakes you up.
Your real problem is an engine that's being starved for fuel. Maybe a floating piece of junk made it's way to the main jet. Jim