Briggs & Stratton 18 HP Twin

[Gregor 4,846]

I mounted the Briggs back on the C-175. I replaced all the wiring on the tractor. As I always do, I checked everything with a continuity meter before I hook up a battery, just to make sure it's all working like I think it should. This one is not working like I think it should, but I may be thinking wrong. This motor has magneto ignition, there are no points and condenser. There are 3 wires coming from the magneto coil. Two spark plug wires, and a small wire that goes to the ignition switch. If I understand magneto ignition correctly, the way to shut off the motor is to ground the small wire coming from the coil. The trouble is, this small wire has continuity to ground, even when it's not connected to anything. I am not quite understanding this. The motor ran fine before I took it off, all I did was paint it. I have not tried to start it yet. I have not even checked for spark. The lug on the switch that the small wire connects to goes to ground when  the key is turned off, but it would not make any difference. The wire is ALWAYS going to ground, according to my meter. Am I thinking wrong? Does anyone know about these Briggs twins?  I would appreciate any help.  Thanks  Greg

[gwest_ca-(File Mod) 11,045]

Are you sure it is ground and not very low ohms - like 1 or 2 ohms? Primary resistance is very low.

 

Garry

[Gregor 4,846]

My meter zeros out.

[Jeff-C175 7,202]

This looks like a good explanation of magneto.

 

https://www.repairfaq.org

 

[Roger R 448]

To properly read the resistance of these you need a good quality meter.  What range is your meter set to?  Rx1 is where you should be. 

[ebinmaine 67,498]

7 hours ago, Gregor said:

The lug on the switch that the small wire connects to goes to ground when  the key is turned off, but it would not make any difference. The wire is ALWAYS going to ground, according to my meter. Am I thinking

 

Does the ignition switch being in "Start or Run" allow the otherwise grounded wire to be NOT grounded while the engine is running?

 

[Gregor 4,846]

19 minutes ago, ebinmaine said:

 

Does the ignition switch being in "Start or Run" allow the otherwise grounded wire to be NOT grounded while the engine is running?

 

Yes   When the switch is turned to run, or start, the lug is no longer grounded. I think this is correct for magneto ignition, but I'm far from being an expert.

[ebinmaine 67,498]

Just now, Gregor said:

Yes   When the switch is turned to run, or start, the lug is no longer grounded. I think this is correct for magneto ignition, but I'm far from being an expert.

 

I'm not by a long shot either but that ground, not ground configuration makes sense to me.

[Gregor 4,846]

I just checked it with my Fluke meter. While it still has continuity to ground, the meter does not zero out.  Maybe I have been worrying about nothing. I guess all I can do is put a battery in it, and see what happens.

[Gregor 4,846]

I hooked up a spark tester and spun it over. The dam thing started right up! Another case where a little knowledge is a dangerous thing.

[ebinmaine 67,498]

3 minutes ago, Gregor said:

 a little knowledge is a dangerous thing.

Hahahahaha. 

 

I try as hard as I can not to learn anything new on any given day but this website messes that up almost every time!

[Gregor 4,846]

Six months ago I didn't know the difference between magneto and battery ignition. Now I know just enough to worry about things. I'm not sure if that's good or bad.

 

I was really surprised when it started up, as there is no fuel line connected to it yet. Must have been enough left in the carb.

Edited June 29, 2021 by Gregor

[gwest_ca-(File Mod) 11,045]

1 hour ago, Gregor said:

Six months ago I didn't know the difference between magneto and battery ignition. Now I know just enough to worry about things. I'm not sure if that's good or bad.

 

That's a good thing. You have likely seen warnings about keeping battery power away from the magneto ignition wires.

The reason is that 1-2 ohms is 1-2 ohms away from a dead short and the very fine wire at the end of the ignition wire can't take the high current = smoke and new magneto coils.

 

Garry

[8ntruck 7,004]

 You don't want to let the magic smoke escape.  It won't work anymore if it does .