I have a 20hp Briggs twin would not start so took plug out and grounded it at the plug hole and the engine started put plug back in and no start. I have had this happen on a Briggs 5hp a few years ago.
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Had a Briggs opposed twin a few years back that would only run if one cylinder was disconnected and not grounded, short in the ignition armature. The opposed twin single module uses both ends of the secondary winding to fire the plugs. The single cylinder engine problem may be related to rust on the flywheel, even though briggs says it won't effect igntion, or low induction of the igntion module but somethings just can't be explained.
I have a customer that farms and has a honda engine on a hopper wagon to fill the planter. he will replace the plug, clean the carb, replace the fuel and still won't start. He will drive it the 8 miles to my shop and i will start it on the first pull every time. Has happened 3 times in the last year.