This good tractor started missing out. Instead of the consistent, steady hum from the engine it Hums for a split second, falters, immediately recovers, Hums, falters, etc. (HUM, cough-cough, HUM). It does this under a load and while idling. It does not seem to lose any power. It just HUMS, coughs and HUMS.
I checked the plugs with an inline spark tester. All 3 cylinders are sparking. Installed a new fuel pump a couple of months ago and it was running very well. Fuel flow seems to be ok.
Carb should be free of carbon as I always use a fuel additive.
Any thoughts on the most logical problem area (carb, distributor, etc)?? Thanks for any advice!!