70 horse lacking power

Hi all! New to the forum, not to boating though........I'm a 30 year veteran mechanic and my parents owned a Johnson/glasstron dealership in Vermont for many years....Anyway, last summer I picked up a 1974 Johnson 70ESL74M off the junk pile at my local boat dealer for next to nothing, spent the winter going through it and finally got to take it out last weekend and found that the motor started and ran perfect, but didn't have the power to get my seanymph striper over 10 mph. it would learch forward briefly like it wanted to take off then settle down at what I would consider to be about 1/3 power. So far this year the motor got new plugs, water pump, fuel pump and lines, carb rebuild (3), head gasket and assorted other odds and end. compression is 100 to 110 on all. so what stupid little thing am I forgetting?

I also cleared the exhaust which was completely plugged and of course changed the gear oil.

Do a cylinder drop test on it and see if you have a cylinder not firing. Your spark should also jump a 7/16" open air gap on a tester.

been there done that, when I first got the motor #3 cyl was dead, it has been fixxed

i'm pretty sure I found the problem, the new #3 coil starts leaking fire above 2500 RPM, so im sure that's the issue

Where's it leaking fire ??

the body of the coil has a VERY small hair line crack, when the motor is reved up it starts to arc between the coil body and bracket. I never would have seen it if I hadn't been working on the motor after dark........weird it was fine at idle though

the varnish or shellac or whatever those coils are dipped in cracks with time...some will run fine in dry conditions and fail in wet weather etc...i think they would also dry out and crack in storage also and you would end up with a new bad one..i have always thought a coat of varnish would be a good pm activity on them...