starting up 340 that's been sitting for a few years

Many good ideas. It is a simple matter of elimination. Check to see if you are getting fuel. Easy enough, remove the fuel line from the carburetor, place the line into a jar or can or whatever, have someone crank the engine. If it is pumping, you will know, naturally if it doesn't pump, you need a new pump. Next, be sure the carburetor is actually squirting fuel, next, check spark, no spark check components. Not much to it!!