1986 Johnson 140 (J140TXCD) Inconsistent start and shuts down when running.

Frustrated...here is the history...had boat running wide open on river and engine stopped dead. I was able to start right up. This happened 3 more times. I just installed new batteries so I tightened down on the cables thinking it was a ground problem. Next time out it wouldn't start. Took it in...mechanic said the carbs needed adjustment. Next time out, engine fired right up, engine cut out 20 feet from ramp, and wouldn't start up again. Mechanic said I needed a new gasket between cylinders. Next time out, it started right up, but I warmed it up thoroughly at the launch (I'm no dummy). 50 feet out from the ramp the engine died. Would not restart. Checked spark...no spark. Home in the driveway...checking for loose wires etc. Checked spark again...none. Mechanic told me to check check peak volts while cranking (we were thinking power pack or stator...while cranking, the engine fires up. It has started everytime since (still in driveway). This sounds like a loose, grounded or damaged wire to me. But cannot locate anything that looks in need of repair. Any ideas?

The ignition is not tied to the batteries.----Motor will run with dead 12 volt battery !-----------Look for problems in the kill circuit ( black / yellow stripe wire ) in control box / key switch.

1986 140hp Johnson..... There are no carburetor adjustments on that model. All fuel measurements are via fixed jets. A new gasket between cylinders?? Where is this gasket?

Does that engine stop like it is running out of fuel, or like you turned the key off?

When you have no spark...... Remove spark plugs... Double check to make sure you have no spark... If no spark, disconnect the large RED electrical connector at the engine... Now, use a small jumper from the large positive battery cable terminal of the starter solenoid to the small 3/8" nut terminal of the solenoid that energizes the solenoid to test for spark again.

If you have spark with that large electrical connector pulled apart BUT no spark with it connected, that indicates there is an intermitent short within the ignition switch, in which case, replace the ignition switch.

Let us know what you find.

The engine stops like I turned the key off. I will check spark with the plug disconnected and jumping solenoid from the positive battery cable.

I appreciate the responses. I apologize for my absence and lack of reply. Mechenic had my boat since December. Said he checked everything out, adjusted timing, but could not duplicate my problem...engine always started and never cut out. I had it in the driveway one week. Took it out on the Delaware River Sunday, cruising up river for 20 minutes...ran fine, idled, checked reverse, put into gear for return and engine stopped dead. NO SPARK. Towed back to ramp.

At home, disconnected the Black wire with Yellow stripe...engine fired up immediately. Tried it 3 more times and it started each time. Reconnected the Black/Yellow stripe and engine started once again. Is it possibly for engine not to start, jostle that Blk?Yellow Stripe wire and it starts?
Am I on the righth track?

Any advice on next step?

It would have been better if you could have checked the spark immediately when the engine died via disconnecting the RED plug rather than to let the engine sit awhile. However...........

In the water, with that black/yellow wire disconnected, if you have no problems and the engine runs as it should for the entire outing.... replace the ignition switch.