1967 Johnson 40 Seahorse Vacuum Switch question

[toadshade]

New to this forum. This is my first "real" boat. First outboard, so I am new to a lot of the parts and workings of these engines. So far I have done some basic PM's to the engine. But a lot of things are not working (Even though the engine fires right up and runs great). One of the disconnected items is the vacuum switch and the idle switch. I know the vacuum switch cuts out one cylinder during a runaway, but my question is, why would someone disconnect it? Basically, what could have been happening to the engine that would cause someone to disconnect the device. Therefore, when I install a new one, what would be the likely outcome, and what should ACTUALLY be fixed instead of disconnecting the switch.

 

[kdiddle]

I have to assume the cut out switch might've been faulty - and in typical PO fashion, they just bypassed it to 'bush fix' their issue. 'Temporary fixes' are never actually temporary. If you replace it, I can't imagine it causing any new issues - as all it does is ground one set of points so they won't fire when its triggered.

I have a similar engine - these beauties are pretty simple, only word of caution I would provide is make sure impeller is in great shape. It should be spraying tons of water out the exhaust. If you haven't replaced it yourself, I'd assume its bad and replace anyway. Plus you get to learn how to disassemble your lower unit and its really not a bad job TBO...impeller cost is also very minimal and cheap insurance for a blown motor.

 

[toadshade]

OK thanks. Device sounds simple enough. I still can't imagine what reason a person would have for disconnecting it. I suppose when I take it apart, I will find that the contact is corroded or broken causing a full time short hence one dead cylinder. Does a high vacuum close the contact or loss of vacuum? Reason for asking is could it have been as simple as a vacuum leak that could cause the contact to close?

Replacing the impeller was the first thing I did. I at least knew that much about outboards. It was a great intro to the lower unit. Good thing I did too. The impeller was ruined.

 

[racerone]

People disconnect this stuff because they have no clue.---Desperate to try things..------I do not believe I have ever seen one of those vacuum switches that failed..----A vacuum leak would NOT close the contact in it.

 

[F_R]

It happens all the time. People don't understand how or why stuff works. So if they experience any sort of problems, no matter what, the first thing they do is get rid of that stuff they don't understand---and the vacuum cut-out switch is one of the first things they head for.

Fact is the vacuum cut-out switch cannot do anything unless there is a high vacuum in the intake manifold, such as occurs during runaway. The high vacuum closes the switch, cutting the ignition to one cylinder till the rpm is under control. Again, the switch cannot close without the presence of a high vacuum. It just cannot.

Another fact is the safety switch prevents the operation of the vacuum cut-out switch at conditions of high vacuum other than runaway. Such conditions are possible at cruise throttle position.

Thirdly, the safety switch serves dual purpose of preventing the electric starter from operating at high throttle settings. It is a SAFETY item to prevent running over the dock----or a person.

 

[toadshade]

As for the safety switch (neutral switch?) preventing starting at high throttle, that was another nice little gift from the previous owner. It is not there. I thought that switch was a seperate device that was connected to the vacuum switch. It is located under the flywheel. I found out when I tried to find a place for the white wire that was disconnected on the vacuum switch. I was going to get that in at the same time as the vacuum. BTW, the overheat light and alarm were all disconnected. I cannot believe the boat was not run 500 feet up a bank by now. There were no safeties on the engine at all. I just don't see how, if any of these devices were causing engine problems so often that disconnecting them made it less annoying to drive the boat, that the engine did not die long ago.

 

[racerone]

People do amazing things to outboard motors.

 

[toadshade]

So since the neutral switch came up, can someone tell me if that is a separate component or is it working together along with the vacuum switch? Is it possible the vacuum switch was disconnected because the neutral switch was removed? I am just envisioning being disappointed after installing the correct safeties and I can no longer start the engine which currently starts up after half a rotation.

 

[F_R]

1. The vacuum switch (VS) is mounted on plastic. So even if it closes it won't do anything, because it isn't grounded
2. The neutral safety switch (NS) grounds the case of the vacuum switch, so the VS is able to function if it (VS) closes But the NS only grounds the VS at slow throttle settings.
3. Since the starter solenoid is grounded to the VS and the VS is only grounded when the NS is at slow throttle settings, the starter solenoid will only operate at slow throttle settings also.
4. The NS is a micro switch mounted on a little bracket at the top of the exhaust cover on the side of the motor (hunker down and look below the flywheel to see it). It is turned on or off by a cam on the bottom of the magneto armature plate as the throttle is advanced/retarded.
5. Sound confusing? It's MUCH simpler than it sounds.

 

[F_R]

Like this

 

[toadshade]

No that is a great explanation. I appreciate it. Will the neutral switch need any adjustment when it is installed? As I mentioned, it is not even there right now. So I never saw it installed. I have looked around but as expected, I cannot find any good photos of what it looks like in place. I had to order the bracket as well, so can you tell me if it simply bolts in place or will I need to make adjustments once it is in?

Also, does that mean that if the throttle is up and I try to start the engine, it will start but die quickly as soon as it reaches a high rpm? Will it in effect, choke itself back and forth therefore just running rough?

 

[F_R]

1. It does require simple adjustment so it opens and closes properly.
2. No, it should not start at all, with the throttle up. It could be rope started, but that's a different topic.
3. You are still trying to inter-relate the two switches. They are two separate switches that happen to share some connection points, but doing separate functions.

BTW, hoping not to further confuse you, but the throttle can not be advanced very far with the shift in neutral. Thus the starter won'r run unless it is in neutral AND at a slow throttle setting. As for adjusting the safety switch, with the shift in neutral the switch should be closed with any available throttle setting (while in neutral) But put it in gear and the throttle can be advanced further, which will open the switch and prevent starting.

I should have began this discussion with a class on Electricity 101.

 

[kdiddle]

Great explanation and diagram, F_R. Toadshade, just to expound on what he said - the neutral safety switch both prevents starter from engaging when in gear and it also prevents you from even pushing the throttle much past high idle when in neutral. As F_R said, you can put in gear and throttle it all you want, but then the starter won't engage. At least on mine, I'm not able to 'rev' engine in neutral much at all without manually pushing the throttle plate through the cowl door. Of course - none of this applies to you yet until you get both items replaced. But I definitely think the minor cost would be well worth the safety factor gained by replacing them both.

 

[toadshade]

OK great. I have the switches on order so it will be nice to have the engine back in working order. At least in that respect. This has been a big help