NGC - small engine ignition troubles

[brider]

Apologies up front for another NGC post....my tractor forum ID expired and they sent the confirmation e-mail to an out-of-date address, and you guys know anything they do anyway...

I have a tractor with a Kohler K341 single, 16hp, with battery ignition. End of last season I couldn't get it started, so I released the hydro valves and pushed it into the shed. Just this weekend (it's my leaf-collection tractor) I replaced the points & coil, adjusted the points to .020 gap and the plug to .035 gap (it WAS at .030-ish). After turning it over a few times, I re-checked the points and they checked closer to .018, but I left them alone because it's a major PIA to adjust them on this engine.

Bottom line, there is no spark at the plug OR at the points, even though I think I shouldn't see the points arcing. Here is the system and observations:





It just occurred to me that maybe my opening the gap on the plug made it excessive, but then, it didn't run at the original gap. Also, could the low point gap result in too little "dwell"?

So, what next to check on this VERY simple system? I did NOT change the plug (it looked to be in very good shape) OR the condensor....I have a new condensor for a Tonti I was going to swap in, but the mount hole was too small and I didn't know if it was the same "spec" as the Kohler?

Kind of stumped, but I'm sure it's simple. Thoughts?

[nc43bsa]

What I would do:

1) Replace the condenser with the Tonti condenser.  For diagnostic purposes, one condenser is as good as another.
2) Turn the crank so the points are open. Turn the switch on and short the points momentarily with a screwdriver;  if you have spark, button everything up and see if it runs.

[MikeP996]

 Sounds like the points are grounded.   It is possible  to easily and accidentally ground the points by improperly installing the lead wire to the points.  Check carefully to be sure any insulators are in the correct position in relation to the lead wire.

[brider]

Sounds like the points are grounded.   It is possible  to easily and accidentally ground the points by improperly installing the lead wire to the points.  Check carefully to be sure any insulators are in the correct position in relation to the lead wire.

THIS is interesting....I recall attaching the lead wire by the glow of a fading headlamp with by bad eyesight...it was all a dimly-lit blur but that is one simple connection, wonder how I could've screwed it up? I'll definitely look more closely with better light.

And the check nc43bsa suggests, is that to verify that the coil will send a charge to spark the plug?

[brider]

UPDATE:

I installed the Tonti condensor (local equipment supply house wanted $45 for an OEM Kohler condensor!) and a new spark plug. Turned it over, no spark. Then I did the test nc43BSA suggested, got an arc across the points but no spark at the plug. Swapped in a new automotive plug wire for the hi-tension plug lead, again no spark.

I am really baffled. I don't think I've ever worked on such a simple system where I couldn't get a fat spark at the plug.

I have the plug clamped to a lifting lug bolted to a head bolt as shown in this highly technical sketch, and I checked continuity from the plug to the batt (-) before testing:





Any further thoughts? I've replaced every part of the system.

[michaell32]

I was always taught when measuring voltage, current needs to be flowing for it to be accurate. Ignition systems make that hard. I would do a continuity test on the ignition switch to see if you are losing voltage going to the coil once the points ground.

[MikeP996]

Just to clarify the process - A spark is generated when the points OPEN, not when they close.  When they are closed, power is (should be) flowing to the coil.  This is the "dwell time" -  the coil is being charged.  Then, when the points OPEN, the electric field in the coil collapses which generates the spark.

If power is flowing through the points and no spark is being generated at the plug ASSUMING the plug is properly grounded on the engine, the coil or its connections are at fault.  FWIW, you don't really need the plug for the test, just arrange to hold the spark plug end of the coil wire within about 1/8 inch from the engine block.

[brider]

If power is flowing through the points and no spark is being generated at the plug ASSUMING the plug is properly grounded on the engine, the coil or its connections are at fault.  FWIW, you don't really need the plug for the test, just arrange to hold the spark plug end of the coil wire within about 1/8 inch from the engine block.

For power flowing through the points, we're talking basically when they're closed, key on, my light probe will light when touched to the fixed contact & ground, right?

For the coil: It's NOS Kohler from a box I've had for 15 yrs banging around the garage. I assume there's a method I can look up to bench-test it?

I haven't yet measured voltage to the coil (+) with key on.....

[n3303j]

Fixed contact is connected directly to frame ground at all times.
Coil is always supplied POSITIVE current from the battery when the ignition is switched ON.
The moveable point is wired to the NEGATIVE (ground) side of the coil.
When the points are OPEN there can be no current flow through the coil because the open moveable point has no connection to ground.
When the points are closed the current moves from the battery, through the ignition switch, through the coil, through the closed points and into frame ground (which should match battery NEGATIVE.

[brider]

When the points are OPEN there can be no current flow through the coil because the open moveable point has no connection to ground.

And referring to the generic diagram in my original post, with the points open, there is NO parallel path (current flow thru coil) to ground thru the condensor, based on the design/function of the condensor?

[n3303j]

Condenser doesn't conduct a lot at 12VDC. Not enough to charge the coil.
But when you open the circuit with the points and the magnetic field inside the coil collapses it generates a current in both the primary winding connected to your points and the secondary winding connected to your spark plug.
The spark plug dumps this secondary winding energy surge through the gap to ground.
Most of the primary winding surge is dumped into the capacitor and it bleeds to ground. Without this path the points would arc extremely at every opening and would burn out quickly.

[brider]

OK, new data:

With points OPEN, I verified that the (-) lead to the points is NOT grounding (as an earlier contributor questioned), and the fixed contact is grounded.

With points OPEN and ignition ON, I measured 12.3 V to the coil (+), 12.3V to the coil (-), and 12.3V to the points (-) contact.

Does this tell me anything?

[MikeP996]

IF I'm understanding correctly how you checked the voltage, it indicates that the primary windings of the coil are not broken but that's all.  I'm assuming you put the black probe of the multimeter on the engine block (ground) and the red probe on coil's + terminal, then moved the red probe to the coil's - terminal, then to where the wire from the coil connects to the points.  As you found, there should be battery voltage at those points with the ignition on/points open.  The circuit to charge the coil is not complete until the points close.  Then, when the points open, the spark is generated.

Check to be sure the points are opening AND closing as you turn the engine over by hand.  If the points do not close due to incorrect adjustment there will be no ignition.  Check this with the multimeter to be sure they are ELECTRICALLY closing, not that they APPEAR to be closing.

FWIW A shorted capacitor (condenser) will render the system inoperative since it will act as a ground and complete the circuit regardless of what the points are doing.

[Tony F]

Are the points clean? I know they are new but a quick wipe with a points file of some emery paper might solve the problem.

Check the resistance in the HT lead. If its aged, particularly if its a carbon lead, it may be open circut.

[brider]

  If the points do not close due to incorrect adjustment there will be no ignition.  Check this with the multimeter to be sure they are ELECTRICALLY closing, not that they APPEAR to be closing.

To paraphrase Forrest Gump's drill sergeant: Mike, you are a goddamned genius! And so were all you others who were spot-on with your suggestions. For all the checks I made, I did not think to check the flow thru the points when closed.

IT WAS THE POINTS! Specifically, the new set of points (that had been sitting on the shelf for 15 yrs) would not conduct with the contacts closed. I cleaned them, filed them, but no continuity across them. That itself is a mystery.

Rummaged thru the trash and found the old points (which may have been original, I did not touch them in the 15 yrs I owned the tractor and it's 46+ yrs old), did a DMM check and they checked good even without cleaning. Not pitted, either. Installed them, gapped them, checked them again with contacts closed, turned it over and FAT spark at the plug! Oh Frabjous Day! With a few sprits of starting fluid the tractor fired up and then idled happily, something it wouldn't do last season and the first symptom of impending trouble.

Learned a lot with this little science project, and like I said at the beginning, you guys know anything they (the tractor guys...) know anyway.

Thanks to all!

[n3303j]

Some sort of oxide forms on some point materials and it is HARD and NONCONDUCTIVE. Used to have an Ariens snow blower that lived in a damp environment. If it didn't run every year then it wouldn't start. The points became nonconductive. I would restore them with about ten minutes of dragging #600 wet/dry paper between them under point spring pressure. I think wet/dry is silicon carbide abrasive. I think points are tungsten. Whatever, points not in use can form a hard, insulating, INVISIBLE coating that renders them useless (As you have just discovered).

Glad it's fixed.

[brider]

Glad it's fixed.

Amen, brother, and thanks for your input.

Used to have an Ariens snow blower...

Did I mention that the tractor in question is an Ariens?

[John A]

A good way to clean the points after filing or sanding is a business card with some solvent rotated between the contacts. If you pull the card through it will leave fiber on the contacts. I do it until it doesn’t leave a spot on the card. Finally a use for all those old business cards!

[MikeP996]

Glad you sorted it out!!!   

[brider]

Since I replaced everything except the points & plug lead, I don't know WHAT the original problem was.

[RinkRat II]

Since I replaced everything except the points & plug lead, I don't know WHAT the original problem was.

     Carburetor 

    Paul B

[SIR REAL ED]

     Carburetor 

    Paul B

As "they" say 90% of ignition problems are carburation....