Ignition System Tips & Troubleshooting
Most people assume the coils or spark plugs to be at
fault whenever there is an ignition problem, such as poor performance or
“missing”.
Usually it is some other problem, and pulling the coils
or plugs out may temporarily resolve that problem…..until the next time.
Things to check:
First check the carburetor adjustment. The correct way to adjust is to run the
engine at moderate speed, then turn the mixture control in or clockwise until the
engine sputters, then turn it back a half turn.
Also check for vacuum leaks in the gaskets. This is the problem when it runs good at high
speed, but needs a different (richer) adjustment at idle.
Then look at the ignition system.
A good way to test to see if all circuits are good up
to the timer is to remove the timer housing and touch each terminal to
ground. The respective coil should buzz
(be sure the ignition is turned on bat).
Also touch the housing to ground to make sure that terminals are not
shorted to the timer case. Check the timer to make sure it is not shorting out
at one terminal when moved by the advance lever, and that it is cleaned and
adjusted per manufacturer’s recommendations.
Some timers require frequent service.
If all coils buzz when the respective timer terminal is grounded, then
make sure the coil is producing a spark at the spark plug by touching a
screwdriver to the plug and to ground (the head).
If you have spark there, but the engine still
“misses” on one cylinder, then it may be a spark plug problem….clean and
re-gap.
If that did not fix the problem, or if the problem is
intermittent, here are some things to check:
Make sure you have power to the coil box with the
ignition switch on “bat”. Use a test
light made from an old car tail light socket and bulb and touch one wire to the
terminal and the other to ground. (test
the test light first across a battery to make sure it is good). If it lights, you have power that far. If not, check battery connections, the
connection at the starter switch, the ignition switch and terminal block. You can use your test light to see if power
is present that far.
If you do have power at the coil box terminal, then
check to see if there is power to the bottom strip of the coil box by touching
your test light to the strip. If you do
not have power there, there may be a connection problem or broken wire from the
terminal to the bottom strip. (It could
be the switch if you have an early model with coil box mounted switch). Make sure the strip is clean and is making
good contact with the coils by slightly bending the strip’s contact tips
upward.
If you have power on the bottom strip, then clean and
bend the terminals slightly out on the strips on the back of the coil box to
make sure of good contact to the coils.
Check the alignment of the coil contacts to the coil box contacts. You may have to shim the coils one way or the
other to get good contact. Replace the
coils in the box. Now you know that you
have power to the coils and good contact with the coils.
Next, check the connections through the back of the
coil box by using a jumper wire to ground each top terminal of the coil
box. The coil should buzz. If one coil does not, switch with another to
see if it is the coil or the coil box slot at fault. If the “good” coil doesn’t buzz either, there
is probably a poor connection where the stud goes through the coil box and
connects to the terminal. Remove and
clean these studs with a wire brush. If
all coils buzz when grounded, then all that is left is the wiring to the timer
and the timer. Ground each terminal at
the timer to see if the wiring is good.
Be sure to ground the timer case to see if it is shorted
internally. If the coils buzz when the
respective timer terminals are grounded, but do not buzz when the engine is
turned, the problem is probably a bad or dirty timer.
Note that some replacement wooden back plates for the
coil box can absorb moisture and actually make a conductive carbon track to ground. I have seen this several times where all
would seem to be well with the circuits and even spark to the spark plug, but
enough spark was “drained” by the back plate that the engine would not fire
right. Note that I offer an oak coil box back plate made by
Steve Tanck of
Note that some cam shafts have the pin hole drilled
through and so the rotor can be installed 180 degrees off. If everything checks out but it won’t run,
and you just changed the timer, check to see if this is the problem.
This is an attempt to cover some of the potential
trouble areas that may be encountered with the Model T Ford Ignition
System. It is surely not complete, and
your comments or additions are welcome.
Frank’s Timer Service, 2251 Morgan Lane, Ingleside, TX 78362
Telephone: 361-230-0318, e-mail: Frank@andersontimer.com