Coil Gap question

I've heard some folks use a business card to set the coil gap. Just to see what my coil gap was I did a google search. I found my Kawa FC420V gap setting but was confused by some others that had 2 numbers. What exactly does it mean when it says something like .012 - .050 ?
Kawasaki Coil Gaps
FC401V .012
FC420V .012 <-mine
FC540V .012
FD440V .018 - .047 <-? does this mean anywhere between .018 and .047 ?
FD501V .018 - .047
FD590V .018 - .047
FD611V .018 - .047
FD680V .010 - .016
FD731V .010 - .016
FD501D .012 - .050

1RB2534 said:

I've heard some folks use a business card to set the coil gap. Just to see what my coil gap was I did a google search. I found my Kawa FC420V gap setting but was confused by some others that had 2 numbers. What exactly does it mean when it says something like .012 - .050 ?
Kawasaki Coil Gaps
FC401V .012
FC420V .012 <-mine
FC540V .012
FD440V .018 - .047 <-? does this mean anywhere between .018 and .047 ?
FD501V .018 - .047
FD590V .018 - .047
FD611V .018 - .047
FD680V .010 - .016
FD731V .010 - .016
FD501D .012 - .050

Click to expand...

You guessed it :thumbsup:

John R said:

You guessed it :thumbsup:

Click to expand...

Thanks for the answer, I guess some coils have enough power to operate in a wider range.

Once Atom Industries patient on the Hall effect magnet Trigger expired all the miserable cheapskate companies who would rather their customers fought with points than pay the 20¢ royalites to use Atoms trigger, fitted Hall effect triggered coils.
If you remember what you should have been taught is high school science, the closer the coil to the magnet the higher the current generated which is the same as increasing the strength of the magnets.
The problem with Hall Effect triggering is when the units get hot the spark retards due to increased resistance ( high school physics again ) in the trigger circuit.
Also the timing is fixed so engine speed is regulated by the amount of fuel only thus an accelerating engine has to run rich or it can not accelerate.
The EPA does not like that idea so many attempts were made to electronically control the timing .
Most were dismal failures and the engine makers eventually got their motors to run really leanly keeping the EPA happy.

Back to your magneto.
The closer to the magnets the pick up is the more advanced the spark will be and the greater the current ( fatness ) in the spark.
Just about every magneto coil will work at .250" away from the magnets, but it will take longer for the magnetic field to generate trip voltage in the Hall Effect trigger so the smaller spark will be latter thus retarding the engine.
You can tune these engines to a limited degree by moving the coil closer or further away from the magnets.
The coil is passive it has no "strength" as such.
Mower engines basically run fixed timing ( another reason why the EPA will force fuel injection ) and as such there is a window for the spark around 5 to 8 degrees of crankshaft rotation where the engine will run because they run quite slow so timing is not as critical.
So kawasaki is simply being honest by giving you a range while Briggs & Kolhler specify an exact amount

Wow, thanks for the detailed summation bertsmobile1, it was most informative. Actually Physics 101 was quite always back for me as I'm in my late 60s. As for the Hall Effect I do (vaguely) remember Edwin Hall who discovered it back in ? (a long time ago). However I do understand the voltage spike that occurs from the coil field collapse when the current is cut off. Of course this occurs from different implementations but with lawn mowers it's usually the magneto apparatus. My limited knowledge of magnetos is that as the magnetic field reaches its maximum (or required) voltage a switch in the control unit opens therein breaking current through coil causing the field collapse voltage spike.

Now your reply really kicks up some notches of my previous understanding of the magneto abilities. I had always just imagined that when the magnet passed the coil collapsed and that was that. But you elaborated the aspect of the coil saturating becoming hotter which increases resistance and retarding the trigger.

I'm a bit rusty on Electronics 101 but guessing to understand the how of what you said I'm envisioning heat induced resistance in the coil lowering voltage through put (in a series circuit) therein increasing the time to reach voltage for control switch to break current therein retarding the coil collapse and spark?

Then you delineated further with the facet of moving the coil further away from the flywheel also effects a timing retard or advance respectively. Since this affects the time of the magneto control circuit getting required voltage for it to open the switch (please correct me where wrong as I enjoy learning these aspects). As you said a sort of crude timing effect not having a distributor to rotate or a programmable CPM box for fuel injection.

When I used to own a Harley (which was fuel injected) I installed a tuner to get around the lower performance of the EPA emission standards forced on Harley in their stock sale products. I had to tap wires into the coils of each cylinder and also tapped the wires going from the crankcase position sensor to the CPM. That allowed a professional putting the bike on a Dynometer to advance or retard the timing by uploading map files with desired timing data. It also allowed to richen or lean the fuel mix. Of course any aggressive advance would warrant very careful listening for knocking or some Dynos have sensors to test for such.

Anyhow thanks for the reply. BTW many decades ago I was in the U.S. Army stationed just a bit northwest of your location doing a year stint in Vietnam. But that was another life all together.

See you knew all along.

It gets a little more complicated becuse the magnet approaching the coil causes current to flow in one direction then the magnet leaving the causes the current to flow in the opposite direction.
but it will all come back to you.

The problem is one of cost and backwards compatiability.

As you know you can not make electricity flow faster ( sub zero temperatures excluded ) so any attempt to apply an advance curve to a magneto , is actually a retard circuit as it is easy to slow electricity down.
So you have to grab the power at its peak, hold it in something ( capacitor ) then wait for the right time to release it and what varies is the release time.
These systems are not as robust as one would hope for and of course it adds substantially to the costs.
'The engines fitted with the controlled ignition systems run so much better than the strait magnetos
However it is hard to sell this to Joe Public that the mower with the 12Hp SAM engine will mow better than the same mower fitted with the 20Hp engine cause we all know that "bigger is better "
Down here we got a 9Hp Kuboa that ran a Kawakasi engine with a controlled ignition.
It was a 38" or 42" deck with Hydro drive and it makes modern 20Hp mowers look stupid.
Similar story with the older JD's, small engines with a really good power delivery system delivered fro the SAM equipted Kohlers, so much better than the latter singles and just not quite as good as the V twin engine at double the rated output.
Also so much more fuel efficient

in reply to bertsmobile1:
I didn't think you could make current flow slower either but I surmise you mean slow the rise in coil voltage by increasing resistance? The rest of your reply reminds me of my much much younger days when I had a 650cc Triumph Bonneville. I loved that bike more than any of the 5 bikes I owned in my life time. Back in those days the aftermarket folks were just starting sell those CD ignition boxes to upgrade bikes like my Triumph. I even bought a CD unit but thieves broke into my apartment and stole the CD unit and my cousin's 30-06 deer rifle. We knew it was an inside job but never found out who. I later sold the bike to pay for some dental work. Good talking with you buddy. Always love talking bout electrical stuff.