Backfiring through the exhaust

I have replaced the twin tower ignition coils on some emergency generators during a emergency and the gen needed immediately by using two automotive coils by connecting the primary windings in series. (have to keep a heads up about correct polarity primaries when connecting in series)

Few years ago the Onan dual tower ignition coils were costly, not readily available and only available from Onan at prices higher than todays clones and long waiting period for a replacement.
 
Forest#2 said:
I have replaced the twin tower ignition coils on some emergency generators during a emergency and the gen needed immediately by using two automotive coils by connecting the primary windings in series. (have to keep a heads up about correct polarity primaries when connecting in series)

Few years ago the Onan dual tower ignition coils were costly, not readily available and only available from Onan at prices higher than todays clones and long waiting period for a replacement.
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All you did was supply 12V and ground to each of the coil's terminals. Series, parallel, whatever.....makes no difference as far as I know. Each gets 12V and ground on the correct terminal. The reluctor wheel's magnet on the crankshaft triggers a Hall effect transistor in the "ignition module" which dumps the primary and induces the secondary to collapse its field and that is dumped to ground thru the spark plug. If there were no module it would be points doing the work. Same thing for the dual tower. There is no magnet passing by a trigger coil to collapse the field induced in the primary by the magnet. So, yes, + is + and - is -....or bad things happen.
 
Dpmulvan said:
How many hours on the mower, what year is it? Is it parked outdoors, any sign of vermin? Sounds like an mis to me not a backfire. Does it get worse when it’s warmed up? If so probably a coil. Start easy,
obvious, before chasing your tail. I’d type more but the pop ups on this site make it ridiculous sometimes.
very annoying.
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Download Origin Ad Blocker for your browser. You are welcome.
 
RevB said:
Grab the cap and pull it off...won't get shocked unless you want to stick your finger in the end...🤔 The voltage isn't enough to each around the insulated cap
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This is a 25 year old mower. Chance could be poor boot insulation or cracked weathered same deal. Guy will get blown out of his socks LOL.

Dude, EXPECT to get shocked messing with high voltage like this.

Use a grounded test light to draw the spark to the probe. Then pull the boot off with gloves on. Keep the probe close to the spark area. Even then beware........
 
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PTmowerMech said:
True that. But what I'm supposed to be looking at is gaps between sparks, instead of a constant blinking, correct? Even with the junk ones like I have, these gaps are visible.
I did notice some gaps in the spark. But they didn't coincide with the backfiring. As in many times there was several back fires in a row, when the sparks were constant.

Maybe there's more to those that are adjustable than I'm aware of. Above my pay grade, sort of speak.
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Spark needs to jump a healthy gap, in free air, to overcome high pressures in the compression stroke. Just because you can see it in free air, doesn't mean it's on time, and enough voltage to jump the plug gap under compression. Adjustable gap testers are king. Any light bulb types are inferior wastes of money.
 
And here I thought the coil to flywheel magnets was 0.010 or a standard business card.

or the service manual puts it Armature Air Gap .008” − .012” (0.20 − 0.30 mm).
 
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