Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Welcome to JUST ANSWER small engines, let me try to help you !! I don't know it all, but maybe together we can get you a satisfactory answer!
run a compression test! Has to be above 80psi for good start. If compression is too low, rings or valve problem.
See what the compression is. Or use finger with rag over the spark plug hole, and see if it has enough compression to move the finger when cranking.
I doubt the weak cylinder is firing. See if it will run on one cylinder. The weak cylinder, may hae a bad valve, check the valve clearance on the weak cylinder.