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1956 30hp Johnson questions

J

James M Camp

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" I have acquired, and am rebu

" I have acquired, and am rebuilding an RD-18 C.
I know the RD-18 designates this as a 1956 30hp but was wondering if anyone can tell me what the "C" following that model number indicates.

Additionally, there is a part bolted to the side with one vacume hose coming from the intake. It somwhat resembles the shape of the old fuel pumps but has no hose connections for fuel lines. This part has a plastic back, and alluminum housing, and a single electrical connector. I know that the wiring was not correct when I picked it up because the lead coming from the starter had a battery terminal on the end of it. I am pretty sure that wire would go to a selinoid, not directly to the battery. Currently, one wire from a coil goes to a togle switch and the other to the connector on that part I am describing. There is also a wire running between the togle switch and the same connector on that part. By sucking on the vacume hose I can hear the part being actuated so I think it is probably good. "
 
The unit is a vacuum switch.

The unit is a vacuum switch. The purpose is to cut out the ignition when slowing down from full throttle and to prevent a runaway condition in nuetral.It was used on the 2 cylinder motors ( OMC ) till the late 60's.Wires are not hooked up to a battery. The battery is only for cranking the motor over and has nothing to do with the ignition.
 
"James..... That part is a vac

"James..... That part is a vacuum controled cutout switch. The wires you speak of are not connected to the coils directly but are rather connected to the ignition points. The coils just happen to connect to the points also.

One set of points (via the wire) is connected to the vacuum switch, and should the engine overrev at any time, reducing the throttle setting sets the vacuum switch in motion/action. This action causes the spark/ignition to cease on one cylinder which efectively allows the rpm to drop down to normal.

Without that vacuum switch, and with a engine running way over its top rated rpms, the throttle would stay open even with the throttle handle turned all the way down. In effect, on a runaway engine, you would have no way to drop the rpms other than to unplug the fuel line.... or close the manual choke. By that time, a connecting rod would most likely be protruding out through the side of the block.

The toggle switch, I would assume, is to cutoff the ignition manually. That wiring is usually from one set of points to the toggle switch, then from the other terminal of the toggle switch to the other set of points.... or to the vacuum switch.

Joe
"
 
" Thanks for the info on what

" Thanks for the info on what that part is for folks. One more question about it though if you would not mind.

Since the only portion of the vacume switch that is in contact with the block in any way at this point would be the back which seems to be some sort of plastic or other composit material that does not look to be a very good conductor of electricity, I make the following observation and ask the resulting question.

Of the four metal screws attaching the plastic back to the metal housing I notice that one of them is about 1/2" to 3/4" longer than the others. The screws are placed into the part from the back which leaves the threads of that longer screw protruding out of the metal housing of the vacume switch. Should there be a wire connected to that longer screw and leading to the block(ground) so that when the switch is activated it makes a connection to ground to shut down that set of points or am I incorrect in thinking that the backing of this part in a non-conductive plastic?

P.S. I knew the lead on the starter, which was set up to connect directly to a battery terminal, has nothing to do with the ignition. I also know that it SHOULD be connected to a selinoid which is normally done using a flat connector with a round hole and not a standard battery terminal connector, which is why I wanted to question the wiring on this part since I was not sure what it was or what it is supposed to do.

Thanks for the info from you both and please, help me out on the rest of the question.

James "
 
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