Small Engines (Lawn Mowers, etc.): 8 horse Tecumseh labors when hot and under load, wheelhorse, condenser

Question
I have a 1970 WheelHorse Charger 8 Hydro.  The 8 horse vert shaft Tecumseh (recently rebuilt)  Starts fine and runs well until hot.  Then when mowing it acts like it is completely over-loaded and will almost chug to a stop.  When I disengage the blades it comes back up to RPM and runs great.  Blades run free when checked, so I know they're not binding.  I had about $600.00 in new parts installed in this motor and it's still not getting it done!

Answer
If you are sure the carb is clean it sounds like a coil to me. The ignition just can't keep up with the load. If the coil is the culprit you will probably need points and condenser again. For sure a condenser.

When you rebuild something like this how much you spent at the machine shop is just as important as parts spending. With this old cast iron motor if you didn't bore to .30 over you really didn't help your power much.