Have an 18hp Briggs Twin that quit and would not start. After detecting a weak spark, replaced plugs and coil. Ran great for two weeks, now week spark again on new coil. Only get strong spark when one coil wire is grounded. Then the other gives strong spark. Could the starter be turning too slow? Is it possible to have two bad coils ? Need some advice

Its not impossible to have two bad coils... it was a oem one right? Might be able to take it back if your lucky... Right now make sure the kill wire isn't grounding any.

Had to get aftermarket not briggs coil, so maybe got taken. Ground circuit works properly. Just wondering if there could also be a starter running slow problem. See a spark the odd time coming from bottom of starter when it is engaged. Other than that all seems in order. Thanks for the reply

As long as its around 300 rpm, it should be good... I've seen them start just barely turning over.

I would check for a good ground or ignition switch loose connection

Check for proper ground or bad magneta

Maybe a shered flywheel key

Sheared key will still give spark, but grounding somewhere is a good thing to check.