It sounds like you might be losing a cylinder under load. Since your carb and compression are good, it has to be something to do with the electrical system.
Dropping a cylinder under load is one sign of a bad spark plug. Have you tried a set of new plugs? Erratic readings with the Tiny Tac could be caused by a weak spark on one cylinder. Try checking the spark plug wires from the plug terminal to ground and both coils should read fairly close. Also check the ground connections on both coils and the power pack for continuity and corrosion. I don’t have the specs handy but I can dig them out later. Also check the spring terminal under the plug boot for corrosion or poor contact with the wires core. They tend to come loose over time and can still show continuity and produce a good spark while testing but can’t supply enough juice to fire the plug while the motor is under load. If wiggling the terminal while hooked up to the ohm meter causes the reading to bounce around, then you know the spring terminal connection is bad.
