Small Engines (Lawn Mowers, etc.): Lawn Tractor chokes/sputters when blades engaged, rockford michigan, inductive timing light

Question
Marc, Recently bought a 6 year old Yard Machine lawn tractor from my neighbor. (18 hp) Two issues: 1) I cut the lawn yesterday 5/18, and after about 1 hour of cutting, I could hear the engine intermittenly "choking" or sputtering if you will.. To the point it almost cut-off. If I disengaged the blades it would recover for a bit, then act up again once I re-engaged into cutting. It eventually totally shut down. My thought bad gas? (Put new gas in prior to cutting) or air filter? 2) My neighbor I bought from says that if you shut the tractor off after cutting, etc and want to re-start it for whatever reason, I have to wait a few hours before it will restart again. I've actually had to wait until the next day to finish one of my lawn cuttings after I ran out of gas! What's the deal? Much obliged for any insight you could provide as I am totally clueless about much to do with engines, etc.

Thanks,

Chip Parker
Rockford, Michigan

Answer
I suspect it has less to do with gas and more related to an issue with heat.  For example, if the engine needs a valve job (burnt valves), the tappet clearance may become insufficient once the engine gets warm.  Then you lose compression.  Generally, you can hear a "whisping" sounds from the exhaust while you crank the engine over (without it starting) if the valves are leaking.  Another heat related issue can be with the ignition.  If the coil is breaking down when it gets warm, you could have the same symptoms.  If you check for spark (should jump 1/8" gap) when it's warm and you have none, the ignition system has a problem.  You can also connect an inductive timing light to the plug leads (one by one) and observe if there is an ignition miss problem (you will be able to see the light skip flashes).  Hope this helps.