Measure ....voltage? to spark plug??

[pacer 3,176]

Got a 17.5 Briggs and spark seems ...weak? and engine is a bit ornery to start, so I'm curious as to how the spark off the coil is measured. Almost certainly the coil is going south, but I got to wondering if/how would/could you check it at the plug wire? Is it AC or DC and what would a good reading be?? Guessing AC cause thats what the internal charging coils are putting out. Just curious........

 

Edit: Guess I should clarify that this is a magneto type.

Edited April 18, 2023 by pacer

[953 nut 58,053]

The power to your spark plug is a single instantaneous high voltage pulse. There are lots of types of ignition spark testers on the market, this is the type I use and the brightness of the momentary light it produces will give an indication of your ignition strength. I am not a B&S man but there is probably a set of breaker points and a condenser under your flywheel as well as the Magneto coil. The condition of the points and condenser has a great deal of impact on the quality of your spark pulse. Coils are binary,  they work or they don't.

Take a look in the reference section for a service manual for your engine. https://www.wheelhorseforum.com/search/?q=B%26S&quick=1&type=downloads_file&nodes=15

[8ntruck 7,402]

Did you try new plugs?  I have a B&S that I used to have to about pull my arm off starting it.  Plug looked good.  Replaced it just for the halibut.  Starts on 1 or 2 pulls now.

[RED-Z06 2,479]

Really isnt a way to test the spark power, its alot of volts..no amps, most testers are a bulb with a universal resistance..if it lights the bulb its adequate, or a Gap style that if it jumps the excessive gap in the tester...its enough.  Cant really go by sight, some light sources, humidity, etc..can make it look blue, orange, pink, white...all of which mean nothing.  If i suspect a bad coil i drop the gap to .020". If it suddenly perks up...coil

[gwest_ca-(File Mod) 11,259]

Spark voltage is likely 15,000 to 25,000 volts. No meter is going to measure that. An oscilloscope was used with automotive ignition testers in the past. They displayed the voltage and the length of time  the spark existed.

[pacer 3,176]

As usual @gwest_ca comes thru and gave me the answer I was looking for -- and that is, you cant get a reading in the typical home shop.

 

A little back ground -- I got this Briggs in a Troy built for $50 and was just curious to see if I could ... bring it back to life?  Well, that hasnt happened yet, I've thrown about $50-60 onto it and while it does 'run' it has about got me frustrated enough to give up on it, what with the huge mess of wiring and just the overall condition - got lots of wear all over.

[kpinnc 13,823]

Some emory cloth across the flywheel magnets tends to help sometimes. They tend to rust over the years, and clearing them off definitely helps.

 

And of course check the magneto gap as well. 

Edited April 20, 2023 by kpinnc

[BESTDOGEVER 218]

The ignition module on Briggs engines are solid state I don't know of any old style (points and condenser) being used in the last 30years. The module is pretty simple if you can observe spark they are good and if not they are done  not much in the way of middle ground. There are coil/magneto testers out there but they cost more than the parts,  ok for a  shop to have kind of overkill for the average guy. 

[pacer 3,176]

This was a whim sort of thing, saw it was only $50 and decided I needed to get familiar with the magneto set-up. I pretty much know the points/condenser system backwards and fwds

 

For a while there I couldnt get it thru my head that that the ign coil did not need any source of external power - it makes it own! As I mentioned the engine runs pretty well, but wont charge the battery. While fooling around with the wiring mess, I was spinning the engine/flywheel with a big electric drill and noticed the spark plug was merrily sparking away... with absolutely no wiring hooked up. Witnessing that cleared a lot of  ...fog? out of my old brain.

 

So, on to the rest of the story, I found the stator was bad and obviously wouldnt charge the battery ---- New stator one the way, and ,,,,maybe this gem  of a lawn tractor may come back to life! 

 

Amazing the differences in it and our horses .... sad!