The first thing to do is verify that it's firing. Do you know how to check that the plug is firing? If so, go ahead and try that first. If not, let me know and I'll explain an easy method.
If the plug is firing, then the obvious things to do are verify that the air cleaner and exhaust are unobstructed. If these both check out, I like to give an engine a little shot of starter fluid to see if the engine has the ability to run. If you do this and get the engine to run briefly, then your trouble is in the fuel system. Check that the fuel line and fuel filter, if it has one, is allowing fuel to flow through. You can just disconnect the fuel line from the carburetor and see if fuel will drain into a glass or some other catch basin. If it will, and the engine will hit on starter fluid, then you'll need to go through the carburetor.
If the carb is mounted directly on the tank, then there's a diaphragm that is likely the cause.
If you can give me the model number off the vac and the make and model number off the engine, I can be more specific. On Craftsman equipment, oftentimes you won't be able to locate the engine numbers. If not, the numbers off the vac should suffice. Thanks, PK.
Small Engine Technician
Owner of a full service shop and national parts sales website.
Sure, just make sure to keep replying to this same question, you won't need to start a new one.
Was the metal you held the plug against part of the head? If so, where is the kill switch located?
Try unplugging the switch if you can. I only have the MTD diagram, the Sears diagram doesn't show the engine and I'm not certain which shut-off you have so if you can describe it that would be helpful.
If you can unplug it easily, then try testing for spark again.
Okay. The kill switch will be on that speed control lever. It should have a wire with a connector that you can just slip off. Take this off and see that the end isn't touching any metal and then see if it will fire.
You'll probably have to remove the air cleaner housing and base to get to it.