Choke solenoid issues on 25 hp johnson

[mdcwells]

I know I should be adding this to my last thread , but I can't seem to get it to post. I blew a primary coil on my 25 hp johnson electric start (melted the points to) I suspected and it was confirmed by many users that 12 volts got up there. I was going over with a voltmeter tonight and seen my choke solenoid is shorted from the 12 volt lug to ground. I pulled it out and I am shorted from the lug to the case. Correct me if I'm wrong the outside of the solenoid is the 12V ground? So if I'm shorted from the lug to ground than this is how I sent a transient voltage through my system.

 

[tashasdaddy]

Re: Choke solenoid issues on 25 hp johnson

very possible.

 

[F_R]

Re: Choke solenoid issues on 25 hp johnson

I know I should be adding this to my last thread , but I can't seem to get it to post. I blew a primary coil on my 25 hp johnson electric start (melted the points to) I suspected and it was confirmed by many users that 12 volts got up there. I was going over with a voltmeter tonight and seen my choke solenoid is shorted from the 12 volt lug to ground. I pulled it out and I am shorted from the lug to the case. Correct me if I'm wrong the outside of the solenoid is the 12V ground? So if I'm shorted from the lug to ground than this is how I sent a transient voltage through my system.

Nah, not. In the first place the solenoid winding is very low resistance. I don't know the exact spec, but probably around an ohm. Would likely be mistaken for a short. If the solenoid works, it is not shorted.

In the second place, there should be absolutely no relationship between any 12 volt items and the magneto. The only thing that even comes close is the ignition switch, and it should not have any connections between 12v and the kill wires either. The usual cause of getting 12v to the magneto is attempting to use the wrong ignition switch. If that is not it, then all we can do is guess. I believe you said you are an electronics tech. You should be able to figure it out--it isn't rocket science.

 

[mdcwells]

Re: Choke solenoid issues on 25 hp johnson

It is an OMC ignition switch. I can take my meter and go from the "m" terminals or the kill switch and have continuity at the 12V side of my solenoid. I pull the wires of the key switch and test it and the switch itself tests good. The choke will engage (which would indicated it's not shorted) It still seems 1 ohm to ground is a short.

 

[mdcwells]

Re: Choke solenoid issues on 25 hp johnson

Could it be possible it needs a diode between 12v and ground?

 

[F_R]

Re: Choke solenoid issues on 25 hp johnson

Could it be possible it needs a diode between 12v and ground?

No. There are no diodes.

As far as the continuity between the m terminals and choke, I don't quite follow you. But both are connected to common ground. The m terminals go to the breaker points, and when the points are closed you will see continuity to ground. Did you say you have a wiring diagram?

 

[mdcwells]

Re: Choke solenoid issues on 25 hp johnson

I have a diagram and that is exactly what I have (ground to the points). Everything looks good and, works good for several outings than it pops. Maybe I should just rewire and hop I find something nicked up that just vibrates into each other.

 

[Silvertip]

Re: Choke solenoid issues on 25 hp johnson

You are an electronics tech and as such you should know there are lots of components that measure 1 ohm. A diode to ground serves no purpose in the choke system because if installed in the forward position it would represent a short to ground when you energized the choke circuit and it would immediately fry the diode. Installed in the reverse direction would make it a "do nothing" element. If you are using an analog meter, set it to x1 and zero it. If using a digital meter it should also be capable of reading 1 ohm. You indicated you rewired the engine side of the system so it is very likely you did something wrong that is allowing +12volts on the coils. It isn't supposed to be there. The engine does not require +12 volts to run since it is a magneto system. This should not be a difficult trouble shoot. We can't see what you did but if you drew a wiring diagram of what you actually have, we could compare it with what you SHOULD have. But then you should be able to do that yourself. I personally feel you have misinterpreted how the two 'M' terminals on the ignition switch are wired. Those have nothing to do with +12 volts. They are simply open circuit with the engine running, and closed to kill the engine. They short the ignition to ground to stop the engine. Concentrate on those two terminals.