Re: 1974 888 spark plug gapping
I have the same engine, but a '76 model. A few boats back, I had the '74 model 888. The Mercruiser manual specifies MR43-T plugs (AC Delco) at a 0.030 gap. I like them since they run well with the stock coil and wires, are about $1.67 each at Rock Auto or about $2.00 each on Amazon.com, and the 5/8" hex makes it easy to get around the stock exhaust manifold logs.
For what it's worth, if the ignition is in good shape, a 0.005" increase in the gap will not make a rat's *** worth of difference and could extend service intervals if carbon fouling is an issue.
I run mine at 0.035" as they come this way in the package and the ground electrode is perfectly aligned (straight and square) and I don't want to mess with it. When I change them every year or two, I check the gap, apply a tiny bit of anti-seize to the last 2 or 3 threads and the sealing chamfer (I use a foam tip swab to keep things tidy), torque them in, and go.
