Small Engines (Lawn Mowers, etc.): 16HP Briggs Surging, carbon residues, air gap

Question
David, I already asked another of the experts and he blew me off with a smarta** answer. If you can't help could you at least post it so maybe someone that had a similar problem could advise me.
I have an old (1972)16hp Briggs Model 326400 (My Father's old Garden Mark Garden Tractor) that's driving me crazy. It will start and idle "all day" fine. As soon as I try to give it any throttle it starts surging, blowing black smoke and dies The original problem was no spark. In the process of getting it going I have replaced the ignition coil, set the air gap at .010, the condenser and points, gapped at .020. Of course the sparkplug is new gapped at .030. That took care of the spark problem. I then started on the surging, redid the carburetor, gave that up and sprung for a new carburetor and was very disappointed when the problem was still there. Did a leakdown test, had about 3-4% leakage. Just a little getting past the rings but from what I've read that percentage is excellent. Tried disconnecting the governor and just giving it gas gently by hand, same thing. I've double checked for air leaks between the carb and the engine, nothing. It's an updraft carb if that helps. I know it used to run fine before it sat for 8 or 9 years. It is a little brute of a tractor when it works so would appreciate anything you could do to help me get it going.
Thanks in advance.
Carl


Answer
Carl,


First Let me apoligize for the other experts conduct He should Be repremaneded for that.
A 3-4% leakage Is excellent Yes But Not efficient the problem is your losing power On compression the compession Is leaking into the crankcase which indicates a worn piston ring replacing the rings should stop this surging. the black smoke is oil Burn with carbon residues
I am trully impressed that a 1972 Is still in operation to this day so you have a True tractor.
Just replace the rings and that will improve the Compression and leakage and stop the surging.