The correct spark plug for the 1991 model, 200 hp Mercury outboard, is a NGK brand, BU8H.
40 hp 2 stroke
The spark plug gap for a 2003 Mercury 125hp outboard motor is .040"
A Mercury outboard will run well with a plug gap of .035 - .040 in.
What is the correct spark plug gap setting for a Mercury outboard 2003 200 HP EFI
spark plug gap for a 1996 mercury 30 hp outboard motor?
What is the spark plug gap for a 9.9hp mercury outboard motor
The 1991 Mercury Marquis spark plug gap is .034. Most spark plugs will be pre-gapped by the spark plug manufacturer.
For a 2005, Mercury 3.3 hp outboard, a NGK BPR6HS.
The correct spark plug gap for the 1982 model, 9.8 hp Mercury outboard is .040 in.
The plug gap for a 9.9hp Mercury outboard, ( all models ), is .035 - .040in.
.035
The 1999 model, 90 hp Mercury outboard requires an NGK BUHW-2 spark plug, standard plug wires are acceptable.
NGK BPR6HS-10 spark plug. Gap is .040