I have a Briggs and Stratton 3.5hp vertical crank engine number 92902. This is a 1976 modal.
I have changed the points, spark plug, and tried a replacement coil of a known working engine (same make and model).
The main problem is this. When the plug cap is on the plug it will not run more than 20 seconds then cuts out and wont restart for 1/4 hour, then does the same.

BUT if i place HT lead without plug cap 1/2 inch away from plug tip it runs like new..

John, April 2008

Thanks John.
Problem now solved by using a new resister cap and plug.
Old rubber cap was slitightly oily on inside causing spark to travel down outside of plug to ground.

John, April 2008

In the days of my motorcycling yore, this indicated a fault with the ignition coil....make sure the points gap is 15 thou though and its always wise to fit a new condenser.

John, April 2008