Marine: Boating, Sailing, PWC, GPS and Navigation - Help with Outboard running rough

I have 1999 Force 90 HP outboard. It was running rough.

My father in law changed the plugs and swapped the lower coil with the middle one. He thinks the middle one (used to be the lower one) is bad. It starts fine & sounds ok but now used gas like crazy.

My father in law is the ultimate shade tree mechanic. Yes it runs now but:

How do I know if the coil is bad & therefore burning more gas?

Thanks for any help.

BG:

wall

The easy way to check if your coil is bad is to remove the spark plugs and ground them out and turn it over and look for spark. If there is one that doesn't have spark swap coils and retest if the spark plug that didn't have spark now does you have found your problem.

I will give it a try in morning. Thanks. I will post the response.