top cylinder cuts out - johnson 33hp

[jdsgrog]

Ok, boating season is coming up in a few months, gotta start working on the boat again.

So, here's the issue. Last season, my '68 johnson 33hp was running great. Got my 14 ft glaspar runabout out of the hole and running about 26-27 mph at wot (gps measure). At the end of the season, my top cylinder cut out. Took it home, checked compression (100+ psi). Checked spark, none to weak spark. Took off the flywheel and checked and replaced everything (coils, condensers, wires, etc.). Still same problem. Checked wiring diagram, so i tried something different, took the wire that is connected to the cut out switch, and checked the spark. Nice, hot, and blue. Reconnected the wire...no spark.

So, is this a cut out switch problem? How does the cut out switch function, or the mechanics of the switch?

 

[tashasdaddy]

Re: top cylinder cuts out - johnson 33hp

the cut off switch ground the coils. also check the mercury switch on the throttle linkage, if the motor was in gear and the throttle was advanced too far, it will kill the spark. safety switch so you do not throw yourself out of the boat.

if you used the put together coil spark plug wire kit. make sure the wires are making contact. the core of the wire has to make contact with the pin in the coils connector. and on the plug end, i always strip back some insulation and wrap wire around the spring, before i put the boot on.

 

[F_R]

Re: top cylinder cuts out - johnson 33hp

Ok, boating season is coming up in a few months, gotta start working on the boat again.

So, here's the issue. Last season, my '68 johnson 33hp was running great. Got my 14 ft glaspar runabout out of the hole and running about 26-27 mph at wot (gps measure). At the end of the season, my top cylinder cut out. Took it home, checked compression (100+ psi). Checked spark, none to weak spark. Took off the flywheel and checked and replaced everything (coils, condensers, wires, etc.). Still same problem. Checked wiring diagram, so i tried something different, took the wire that is connected to the cut out switch, and checked the spark. Nice, hot, and blue. Reconnected the wire...no spark. So, is this a cut out switch problem? How does the cut out switch function, or the mechanics of the switch?

It certainly would seem that the cut-out switch is the problem, except for one glaring thing--the cut-out switch is connected to the bottom cylinder, or at least is supposed to be. So, it should have no effect on the top one.

But to answer your question, the cut-out switch prevents the motor from running wild in a no-load condition. By running wild, I mean that if you somehow rev it up in a no-load condition, it won't slow back down...just keep revving. The cut-out switch monitors the vacuum in the intake manifold and when it senses a run-away condition, it kills the spark in the lower cylinder till it slows back down.

But, there is more to it than that. Under certain conditions, the cut-out might close when it is not supposed to. To prevent that, it is mounted on an insulator and grounded through the safety switch only at low throttle settings. It is not supposed to be grounded at all at high throttle settings, and therefor cannot kill the lower cylinder at high throttle....IF it is properly wired.

The same safety switch also serves another purpose...it prevents electrically starting the motor at high throttle setting.

 

[jdsgrog]

Re: top cylinder cuts out - johnson 33hp

Thanks, for the replies. I'll take a look again at the wiring and make sure it was the coil for the top cylinder. I guess I'll have to look at the whole wiring again. It's been a few months, so I think I'll take a look this week or next.