1973 20HP johnson with intermittent miss

[edhd13]

I have a 1973 20 HP Omc that's making me crazy. It will start good, idle OK, miss slightly getting up on plane, run good on WOT and 3/4 throttle, at less that 3/4 throttle 1 cylinder will completely cut out right down to idle. If I go back to WOT, it will sputter and fart and then pick up it's other cylinder and run fine. If you leave it at low speed, it will run on 1 lung for a good 15 minutes and then the other cylinder will cut back in and run fine indefinitely. This is the later point ignition with the charge coil under the flywheel and 2 coils on the head. I have changed the points, condenser, all 3 coils and the plugs twice, just in case. I've checked the low tension wires between the points and the external coils extensively for open and grounds, since the problem seems throttle position sensitive and found nothing amiss. The compression is good, 100 PSI both holes. While grabbing for straws, I tore down the carb and cleaned it thoroughly and no issues were found. It makes no difference when I swap the primary leads and the spark plug leads on the coils. When I disconnect the kill switch and short the primary wires to ground 1 at a time at this location , the problem seems to be on the bottom cylinder and doesn't change when I switch coil wires. I'm baffled, any ideas???

[boats.net]

Have you replaced the stop switch wires between switch and points, wire may be shorting out.

[edhd13]

I have disconnected the kill switch wires and the problem persists.

[boats.net]

Did you disconnect wires at points? Wires may be short where they go through timing advance plate, which moves as you advance throttle.

[edhd13]

I currently have the mag plate off the motor and on the bench for the second time. The charge coil tests good as do the condensers. The wires are completely disconnected, the grommets are good, no exposed wire anywhere. I put a load on the wires with a battery and a test light and moved, tugged, twisted, stretched them in every conceivable manner. No problem found. I cannot believe that the problem is not the wires as the issue is so throttle position sensitive. I may change the wires anyway, just because of frustration, but I would be surprised if that helps.