[homefried1]

Went to mow the sides of the road in front of the house today and the mower wont crank up. Turns over just fine, just wont fire. Pulled the plugs out and looked for fire, none. Took the cover off the engine exposing the flywheel and the 2 coils, with plug wires coming out to the plugs. Could not see anything wrong.

Now I'm thinking that the coils are grounded out so I start looking and see where each coil has a wire plugged into it on the bottom so I thought I could unplug those, and it should fire, but it didnt. I even went as far as polishing up the magnet on the flywheel though I have laughed at other people doing that before and of course that didnt help.

I dont know where to go next. IF the flywheel is turning, and there are no wires hooked to the coil to ground them out, it should be firing, right?

Thanks for any help!

 

[38racing]

You have not said exactly how you tested for spark to confirm that there is on. It could not be starting for fuel reasons like no power to carb solenoid.

 

[rayjay]

It is highly unlikely that both coils died at the exact same time !!! My first guess is that the motor has had one bad coil for some time and the other coil failed today making the motor not run. If this was the case one plug would have been cruddy and the other looking mostly normal.

 

[homefried1]

You have not said exactly how you tested for spark to confirm that there is on. It could not be starting for fuel reasons like no power to carb solenoid.

At first I just plugged the plugs back into the plug wires and turned the engine to see if I could see fire jumping, which I didnt. Before I quit I was holding the wire in my hand while turning the engine over to see if I could feel any fire, and could not.

 

[homefried1]

It is highly unlikely that both coils died at the exact same time !!! My first guess is that the motor has had one bad coil for some time and the other coil failed today making the motor not run. If this was the case one plug would have been cruddy and the other looking mostly normal.

Best I remember both plugs looked the same. Those wires I spoke of, they would have to be ground wires, dont you think?

 

[bonusbuilt1950]

Put the wires back on the plugs and rze-connect the coil ground wires. Get a can of silicone spray ( do not use starting fluid ) and spray some down the carb throat. Try to start it. If it fires and dies, it is not electrical, but probably a fuel problem. Take the fuel line off the carb and take the plugs wires off the plugs, put the carb hose into a can and crank it over to see if you have fuel squirting into the can. If not, the fuel pump may be bad or the line to it plugged or restricted.
It's hard to check for spark with the way you did it. Make sure the plug is well grounded to the motor and have someone crank it over so you can look closely for a spark. A spark tester or a brand new plug works well as long as it is grounded properly. Take a set of feeler gauges and see what the gap is at each coil and the flywheel by the magnet. The gap should be somewhere in the range of 2-12 thousands. I always set mine at 10 thous.

How was it running before it died?

 

[rayjay]

Best I remember both plugs looked the same. Those wires I spoke of, they would have to be ground wires, dont you think?

Yes, those are the kill wires which ground the coils to kill the spark. With the kill wires disconnected there are only a couple of issues could cause a no spark situation. #1 would be bad coils. Unlikely for both to fail at the same time. #2 would be the signal magnet on the flywheel has failed somehow.

 

[tomw0]

Does this ignition have a diode that prevents one cylinders coil from firing the other cylinder? I have not thought out how it works, but some have a diode that kills the ignition for both cylinders when (at least) one is grounded.
If you have the schematic for the mower, take a look at the ignition coil and ignition switch wiring. I think a diode failure would kill both coil outputs at once. But, don't bet your paycheck.
tom

 

[rayjay]

He disconnected the kill wires from both coils...... Still no spark.

 

[38racing]

He disconnected the kill wires from both coils...... Still no spark.

Except it is not clear if he had no spark. Did he actually have the plugs grounded when he did the spark check.

 

[rayjay]

Except it is not clear if he had no spark. Did he actually have the plugs grounded when he did the spark check.

He held them in his hands and didn't get the heck shocked out of him :thThumbsU

 

[38racing]

He held them in his hands and didn't get the heck shocked out of him :thThumbsU

Reminds me of a childhood visit to my uncle's farm. His brother held the electric fence wire and got no shock. He was wearing rubber boots.

 

[homefried1]

Thanks for all the help guys, but I figured it it myself! The mower is cursed!! Haunted or something, cause when I tried it again, after having done nothing except poking around on it, it fired right up. I am sure there is a bad wire somewhere that got moved while messing with it.

Took it out and mowed about 2 1/2 miles of road shoulder then it broke the drive belt and had to pull it home with my truck.

 

[rayjay]

In 40+ years of fooling with infernal combustion engines the one absolute is that they can always throw you a curve.

My favorite was a Honda XL100 a customer brought me. It sputtered and generally ran poorly. I was messing with the points and with the motor running I could pry the movable arm over with a screwdriver so that it was not touching the fixed point and THE MOTOR WOULD STILL RUN !!!!! I never did figure that anomaly out.

 

[homefried1]

Well, here we go again! Exact same thing is going on again. I have reviewed the replys here from last time, and still have no clue, OR spark. One difference is, I now know that the wires coming from the 2 coils combine into one, and is grounded coming FROM the coils. That doesnt seem right to me. I dont mean the wire going from the ignition switch to the coils, I mean the wires that are plugged into the coils themselves. They shouldnt show a ground should they?

 

[Walt 2002]

The ignition is killed by shorting thru the small wire. I am not sure how you are testing. Sounds like a problem in the "Kill Wire" harness to me as suggested by tomwO. When you tested for spark with both Kill Wires disconnected from the base of the engine, you held the plug wire in your hand with something stuck in it to make contact, did you also touch metal on the engine to ground yourself? And the engine must turn about 800 rpm before it will spark.

Walt Conner

 

[homefried1]

The ignition is killed by shorting thru the small wire. I am not sure how you are testing. Sounds like a problem in the "Kill Wire" harness to me as suggested by tomwO. When you tested for spark with both Kill Wires disconnected from the base of the engine, you held the plug wire in your hand with something stuck in it to make contact, did you also touch metal on the engine to ground yourself? And the engine must turn about 800 rpm before it will spark.

Walt Conner

I tested by hooking a test light to the hot side of the battery, and touching to the wire coming FROM the coils. The light lit up when I touched the point of the test light to the wire.

Reckon one of the coils is bad, causing it to ground, and that is also grounding the other stopping both from firing?

 

[rayjay]

They should only be grounded with the ign sw turned off. With these wires unhooked from the coils you should get spark if the coils are good.

 

[tomw0]

I do not think putting 12v from the battery through a bulb, through the magneto coils is a good idea. You essentially ran the bulbs on the windings of the magneto. I do NOT know if that will damage them, but have seen here regularly that putting voltage to a mag is a no-no.
Magnetos are 'self exciting' coils, developing a smidge of juice to energize the coil winding using one magneto winding, and the second winding developing a spark when the first juice goes away. The magnets on the flywheel cut through the windings of the coil, creating 'juice'. Give the coil external juice, and they may fry.

 

[Walt 2002]

"Reckon one of the coils is bad, causing it to ground, and that is also grounding the other stopping both from firing "

These coils seldom go bad. The diodes in the Kill wiring do go bad and affect the ignition in strange ways however IF you disconnect the Kill wires at the base of each coil then they are completely independent.

NEVER put any battery power to a magneto coil of a B&S engine. Of course the bulb is going to light in your case. I just hope the bulb limited the current enough to not damage anything.

Walt Conner