557 East 3460, Provo, Utah 84604 and Rex A. Whiting, D.D.S., Box
I46, 5I West Center, Heber City, Utah 84032
Often all the mechanical work is complete on a fine little model
gasoline engine, or a grand old restored engine, and then comes the
question; ‘what am I going to do for an ignition system?’
If that is your dilemma, then here is an answer.
To help understand the operation a little better, first
we’ll have a very basic course on electromagnetism.
Whenever electrical current flows thru a conductor such as a
wire, circular magnetic lines of force form around that conductor.
(See Fig. #1)
Now if you take that wire and wrap it into a coil, the magnetic
flux lines complement each other. (See Fig. #2)
If an iron core is placed in the coil, the flux lines will
travel thru the iron. The flux lines like iron because they can
travel thru it much easier than thru air. We have now created an
electro magnet. (See Fig. #3)
There are some peculiar things about electricity and magnetism.
If an electrical current passes thru a conductor, magnetic flux
lines form around the conductor as we have just seen, and inversely
if magnetic lines cross a conductor they cause a current to flow in
that conductor. The latter is how we generate electricity.
Suppose we wrap two coils around an iron core and induce an
electrical current into one coil. We’ll call it the
‘primary coil’. This will cause a magnetic field or flux
lines to build around the iron core. As the flux lines are building
and cut across the wires in the ‘secondary’ coil,
electricity will flow in the secondary coil. This is called
Induction. (See Fig. #4)
Another peculiar thing about the above apparatus is that the
voltage in each of the coils is proportional to the number of turns
in the two windings. In an ignition coil for instance, the primary
coil energized by say a six volt battery would have relatively few
windings, and the secondary coil would have thousands of times more
windings of very small diameter wire in order to get the 15,000 to
25,000 volts needed to jump the gap in the spark plug.
Let’s apply the knowledge we have learned and make a diagram
of an ignition system for a one cylinder gasoline engine.
In the diagram, (Fig. #5) we have put a round head rivet in the
cam gear. The rivet acts as a contact to complete the circuit from
the battery and around thru the primary winding. This contact point
or switch needs to be adjustable so that the timing of the spark
will fire just as the piston comes to the top of the compression
stroke. This adjustment can be as simple as just bending the
contact finger that touches the rivet head. On large engines it is
very desirable to have some means to retard the timing
for starting, and then advancing it for running.
The timing point or contact does not necessarily need to be
located on the cam gear. It can be located on any moving part of
the engine that will cause the switch to close at the proper
In the diagram, (Fig. #5) we are using a buzz coil. This is the
same sort of circuit as was used on the old model T Fords. At rest
the buzz coil points are closed. As the circuit is energized the
iron core magnetizes and pulls the buzz coil points apart which
breaks the circuit and lets the buzz coil points snap back together
again, which energizes the circuit and the process starts all over
again. The result is an almost continuous arc at the spark plug as
long as the timing contacts are closed. If the buzz coil points are
not used as in modern engines, then there is just one snap spark at
the spark plug each time the timing contacts closes and completes
The condenser (or capacitor) is an insignificant looking, but
necessary little contraption. A condenser has the ability to store
and release small amounts of electricity. The best way to describe
it’s function is to compare it to an air dome on a piston type
water pump. Believe it or not, electricity flowing in a circuit has
kenetic energy similar to that of a flywheel. It takes effort to
get it to start moving, and to stop it once it is moving. The
condenser absorbs the surge as the points open and the flow stops.
Arcing at the points is greatly reduced. Then as the points close
again the stored electricity flows back into the circuit along with
electricity from the battery and adds that extra ‘Umpf!’ to
help fire the spark plug.
Now that we know all about electricity and how to wire it up to
our engine, let’s proceed to make a ‘SPARKER’ for our
engine. First we will need to acquire a magneto coil from a small
engine such as a lawn mower engine. Later models will have a more
compact coil than those that were made over fifteen or so years
ago. These coils may vary in shape from the one illustrated, but
they will all work.
You will want to check the coil to make sure that it is good.
This can be done by touching the primary leads to a ‘C’ or
‘D’ size flash light battery while holding thumb and finger
across the high tension lead and the ground wire. You will get a
mild shock if the coil is good.
If you are too much of a ‘Boob’ to make this test
yourself, you might get your wife to hold the high tension lead and
the ground wire while you manipulate the primary leads to touch the
battery, explaining to her that you cannot hold all those wires at
the same time. I can assure you that this method will verify
whether the coil is good, however I need to caution you that your
bodily injuries might be far less if you just perform the test by
With just a flashlight battery for power, the shock that you get
is more of a ‘startle’ than a ‘zap your finger off’
jolt that you get when you touch the spark plug wire of a running
Once the coil is proven good we can proceed to make the sparker
as follows: (See Fig. #6)
The simplest High Tension ignition system is the single spark
ignition system as shown in the diagram above. (Fig. #7)
You can build a small hardwood box of your own design to house
the coil, condenser, and battery.
If all you desire is a single flash spark ignition then you can
stop here. If you desire to build a Buzz coil spark ignition
system, then continue on to the next page.
Note: A condenser from any automotive or small gas engine
ignition system will work in the systems shown on these pages.
Direction of hookup is not critical.
For a buzz coil ignition system start with a mounting board
1/8‘ to 1/4‘ thick.
The board can be any non conductive material such as plastic,
masonite, plywood, or hardwood. Hardwood being the classic
Here is an alternate plan if you would like to make your own
Buzz coil points:
This is not a good picture-B & S coils on later models are
much smaller and a more compact unit can be built.