Backfiring through the exhaust

[PTmowerMech]

this may damage the coil transistors since the High Voltage has to dump somewhere.

Correct not a good thing to pull a plug wire on some ignition systems.
Also
If you have one of these inline spark testers it will also allow grounding the the ignition while the engine is running if the spark plug boot is the molded type and cannot be slide back on the ignition wire for access to the tip of the spark plug.
OREGON SPARK TESTER Repl Briggs 19051 19368

Doesn't the same effect on the coil happen when you run a 2 cylinder on only one plug wire. As in removing one plug wire, starting it, then repeating the process with the other side?

The electricity being created by the coil with the disconnected plug wire has to go somewhere also. Right?

 

[Hammermechanicman]

Look at this wiring diagram from an onan engine. What happens when you disconnect a plug wire to try and run on one cylinder?

 

[Auto Doc's]

Doesn't the same effect on the coil happen when you run a 2 cylinder on only one plug wire. As in removing one plug wire, starting it, then repeating the process with the other side?

The electricity being created by the coil with the disconnected plug wire has to go somewhere also. Right?

Hello PTmowerMech:

An adjustable spark tester is recommended so the coil electric energy will be dissipated. If a plug wire is just left off loose even briefly the coil will overheat and fuse the internal windings.

 

[RevB]

Doesn't the same effect on the coil happen when you run a 2 cylinder on only one plug wire. As in removing one plug wire, starting it, then repeating the process with the other side?

The electricity being created by the coil with the disconnected plug wire has to go somewhere also. Right?

As was stated earlier, better to remove plug, insert into plug cap, and ground the plug to discharge energy via spark.

 

[Forest#2]

View attachment 71570
Look at this wiring diagram from an onan engine. What happens when you disconnect a plug wire to try and run on one cylinder?

this is termed waste spark ignition.
normally when a plug wire is purposely pulled the Onan waste spark ignition engine will not run on the opposite cylinder because the spark plugs are in series. (kills the spark to both cylinders)
To test this system ground the spark plug cable one at a time of kill the engine and insert a grounded spark lug.
But I've seen B43/B48 engines run on one cylinder due to a bad dual tower coil.
Also one size (part number) does not fit all on the Onans. The points and electronic coils are different part numbers.

 

[Auto Doc's]

Hi Forest#2,

The OP is working on a B&S twin not an Onan, but it is good information to know. I occasionally see Onan generators in RV's. Thanks

 

[Hammermechanicman]

this is termed waste spark ignition.
normally when a plug wire is purposely pulled the Onan waste spark ignition engine will not run on the opposite cylinder because the spark plugs are in series. (kills the spark to both cylinders)
To test this system ground the spark plug cable one at a time of kill the engine and insert a grounded spark lug.
But I've seen B43/B48 engines run on one cylinder due to a bad dual tower coil.
Also one size (part number) does not fit all on the Onans. The points and electronic coils are different part numbers.

Exactly. Lots of folks assume onan engines are like most other engines.

 

[RevB]

this is termed waste spark ignition.
normally when a plug wire is purposely pulled the Onan waste spark ignition engine will not run on the opposite cylinder because the spark plugs are in series. (kills the spark to both cylinders)
To test this system ground the spark plug cable one at a time of kill the engine and insert a grounded spark lug.
But I've seen B43/B48 engines run on one cylinder due to a bad dual tower coil.
Also one size (part number) does not fit all on the Onans. The points and electronic coils are different part numbers.

So...on an Onan two cylinder opposed, is there but one coil for both since both would fire at the same time. The only way for plugs to be in series would be on the opposed cylinder models.

But looking at the diagram from post 62 shows the outputs to be in parallel, not series.

Any V configuration would require two coils to service it's particular cylinder but you still get wasted spark there, too.

 

[Forest#2]

So...on an Onan two cylinder opposed, is there but one coil for both since both would fire at the same time. The only way for plugs to be in series would be on the opposed cylinder models.

But looking at the diagram from post 62 shows the outputs to be in parallel, not series.

Any V configuration would require two coils to service it's particular cylinder but you still get wasted spark there, too.

Lots of info on-line about waste spark ignition systems
AND
Onan's waste spark ignition system

 

[Hammermechanicman]

The onan engines are opposed twins