Spark plug only sparking after key is released... ?

[davem1111 1,934]

Hey all, so I picked up this B-100 that I've been talking about in another thread, but decided to create a new thread here for a more focused topic.

 

When I got it, it had nasty gas in it, so I drained everything, pumped out the crap in the fuel pump, and cleaned the carb. I also had pulled the spark plug and cranked it with the plug against the engine and saw a spark. Shot some ether in the spark plug hole, put the plug back in, and it fired a few times. Cool. Put the cleaned carb back together, but it would not run, no firing with ether through the carb.  New lines, just running gas in from an "IV" for now... So I ordered a new carb, it was only $30. Put the new carb on today and she still won't run, but won't even fire with ether shot in through the carb, or isn't getting gas...  Then I tried the plug against the engine, and oddly I noticed that there was no spark while cranking but it sparked a few times when I let off on the key. 

 

Any idea what would cause this?  Problem with the coil or wiring?  

 

I also noticed that there are 2 wires coming from the engine that are not connected to anything. I haven't checked wiring diagrams yet. Anyone know what these are for?

 

 

 

[adsm08 1,442]

Check to make sure the points aren't stuck closed.

 

The way a coil sparks is by building an EM field around a set of windings when it is turned "on" (supplied a power and ground). When it turns "off" (power or ground interrupted) the field collapses, and as it does so it induces a high-voltage charge in the secondary windings, which then discharges through the spark plug.

 

The way we control this in these applications is the key switch turns the power on and off, and the points interrupt the ground to fire it. If your coil only fires when the key is turned off then the points aren't cutting the ground, and so they probably aren't moving.

 

The circuit also won't work properly if the condensor is bad.

Edited June 28, 2022 by adsm08

[Snoopy11 5,713]

That's some knowledge right there @adsm08

 

Aren't those wires for lights or some kind of aftermarket electronics there, Dave? Looks like male and female... newer looking connectors clamped by hand... so dat'd be my best guess... couldn't possibly be E-pto or anything like that...?

 

Don

[Pullstart 59,851]

Without getting into big technical details, I’ve had ignition switches go bad before.  Try checking the coil power to ground while cranking.  You could also disconnect the starter solenoid and just hold the key on start and check for power.  

[squonk 39,006]

Those 2 wires are from the charging stator. They connect to the regulator. Your ignition switch is probably junk.

[RED-Z06 2,131]

Probably the wrong switch or bad switch.  On 12v ignition systems you need 12v to the S(olenoid) for cranking and 12v to a post in both the run and start positions...usually an Accessory post will do this.  G(round) is a given and B(attery) ties into 12v with a fuse.

[davem1111 1,934]

Lots of good ideas here - thanks, guys! 

 

1 hour ago, adsm08 said:

Check to make sure the points aren't stuck closed.

 

The way a coil sparks is by building an EM field around a set of windings when it is turned "on" (supplied a power and ground). When it turns "off" (power or ground interrupted) the field collapses, and as it does so it induces a high-voltage charge in the secondary windings, which then discharges through the spark plug.

 

The way we control this in these applications is the key switch turns the power on and off, and the points interrupt the ground to fire it. If your coil only fires when the key is turned off then the points aren't cutting the ground, and so they probably aren't moving.

 

The circuit also won't work properly if the condensor is bad.

 

Hadn't thought about points or condensor.  Will need to look into those.

 

 

1 hour ago, Snoopy11 said:

That's some knowledge right there @adsm08

 

Aren't those wires for lights or some kind of aftermarket electronics there, Dave? Looks like male and female... newer looking connectors clamped by hand... so dat'd be my best guess... couldn't possibly be E-pto or anything like that...?

 

Don

 

I think what Squonk said is probably right - charging stator. So if this isn't connected, it should run but the battery wouldn't charge?

 

1 hour ago, Pullstart said:

Without getting into big technical details, I’ve had ignition switches go bad before.  Try checking the coil power to ground while cranking.  You could also disconnect the starter solenoid and just hold the key on start and check for power.  

 

Good idea - will try that.

 

58 minutes ago, squonk said:

Those 2 wires are from the charging stator. They connect to the regulator. Your ignition switch is probably junk.

 

Now that you mention it, I'm not sure where the regulator is (or is supposed to be) on this model. Now I strongly suspect that, at best, the wiring has been messed with. At worst, totally FUBAR'd.  I'll get the wiring diagram and see what looks right and what doesn't.

 

9 minutes ago, RED-Z06 said:

Probably the wrong switch or bad switch.  On 12v ignition systems you need 12v to the S(olenoid) for cranking and 12v to a post in both the run and start positions...usually an Accessory post will do this.  G(round) is a given and B(attery) ties into 12v with a fuse.

 

Hmmm... the seller said it ran about 2 years ago, sat inside for a year then outside for a year. So I doubt anyone had messed with the wiring or switch since then, unless they failed at a repair attempt. 

 

I have a non-running 416-8 Kohler here that I can scavange some parts from if necessary, and I'm guessing a switch, points and condensor don't cost a lot. Again, I'll review the wiring diagram and see what it should look like.

 

Thanks!  

[RED-Z06 2,131]

15 minutes ago, davem1111 said:

Lots of good ideas here - thanks, guys! 

 

 

Hadn't thought about points or condensor.  Will need to look into those.

 

 

 

I think what Squonk said is probably right - charging stator. So if this isn't connected, it should run but the battery wouldn't charge?

 

 

Good idea - will try that.

 

 

Now that you mention it, I'm not sure where the regulator is (or is supposed to be) on this model. Now I strongly suspect that, at best, the wiring has been messed with. At worst, totally FUBAR'd.  I'll get the wiring diagram and see what looks right and what doesn't.

 

 

Hmmm... the seller said it ran about 2 years ago, sat inside for a year then outside for a year. So I doubt anyone had messed with the wiring or switch since then, unless they failed at a repair attempt. 

 

I have a non-running 416-8 Kohler here that I can scavange some parts from if necessary, and I'm guessing a switch, points and condensor don't cost a lot. Again, I'll review the wiring diagram and see what it should look like.

 

Thanks!  

 

[Pullstart 59,851]

8 hours ago, davem1111 said:

I have a non-running 416-8 Kohler here that I can scavange some parts from if necessary, and I'm guessing a switch, points and condensor don't cost a lot. Again, I'll review the wiring diagram and see what it should look like.

I believe the Magnum engines are different ignition than K-series engines.  The switch might not have the same terminals to fix your issue 

[gwest_ca-(File Mod) 10,516]

10 hours ago, adsm08 said:

Check to make sure the points aren't stuck closed.

 

The way a coil sparks is by building an EM field around a set of windings when it is turned "on" (supplied a power and ground). When it turns "off" (power or ground interrupted) the field collapses, and as it does so it induces a high-voltage charge in the secondary windings, which then discharges through the spark plug.

 

The way we control this in these applications is the key switch turns the power on and off, and the points interrupt the ground to fire it. If your coil only fires when the key is turned off then the points aren't cutting the ground, and so they probably aren't moving.

 

The circuit also won't work properly if the condensor is bad.

Try this with the points cover removed in case the wiring is shorting against the cover.

[953 nut 51,940]

37 minutes ago, Pullstart said:

I believe the Magnum engines are different ignition than K-series engines.  The switch might not have the same terminals to fix your issue 

                   This thread that Garry and I did will show you how they don't play well together.

 

[Tuneup 1,416]

So Dave, I read that it did kick with starting fluid so I'm thinking the points are OK - unless something happened in the interim. Connect a lead from battery (+) to the + on the coil and crank it - should have a spark on both cranking and ignition on. If not, coil or points or plug or cap. If so, check the wiring and ignition switch. If the cap is bad, you can at least disconnect it and test for a spark and a good start. It won't rev and will likely backfire but it's a good cap test. Those switches are general garbage and who knows what the prior owner put in there. I repaired a tractor once that had a bad switch and the replacement that came was the wrong one. Had to install a diode to make it all right. Anyway, GOOD LUCK! Simple old tractor that is pretty easy to diagnose. Oh, you should get AC from those open leads when connected across a DMM.

[crusher 0]

Hi Dave, I'm experiencing the exact same issue, did you ever resolve this?

[Gasaholic 183]

1 hour ago, crusher said:

Hi Dave, I'm experiencing the exact same issue, did you ever resolve this?

Common problem with spark not happening (on K series battery ignition) until key is let off start (to run position): Bad switch (#1) , or wrong switch (Someone put magneto ignition switch in place of battery ignition switch) - Another common cause is a bad ground strap on machines equipped with rubber motor mounts, or a bad ground in general (High resistance not allowing enough voltage to flow through coil to points), or a corroded glass fuse holder (Again high resistance causing low voltage to coil)  - Basically whatever is causing insufficient voltage through coil while cranking, but allows voltage once key is returned to run position. There's been a few UNCOMMON things I have found over the years, but so rare as to be unlikely to not be one of the above issues.