From:john b cross
Subject:RE: RE: 63 scat no fire Date:Sat Mar 31 21:57:44 2018
Response to:22589


The Service Manual tells us that we should never energize
either of the coils in the magneto with a battery while the
coil is physically in the magneto, as this can partially
demagnetize the rotor.

Play it safe and disconnect things before testing them. To
test the coils, remove them from the magneto. This
includes testing with an ohmmeter, as the ohmmeter
contains a small battery.

You will need a multimeter that has an ohmmeter, a small 6v
battery (a lantern battery, or the $6 gel-cell we use on
battery bikes), and some hunks of wires with alligator

You didn't say whether this bike is new to you. If it is,
perhaps the previous owner wired it incorrectly. It will
never start if it's wired wrong! Use the Scat wiring
diagram (in How-To-Restore), and rotate it so the headlight
points up. Note: The lower coil and upper points run the
ignition. The lower points run the stop light.

Trace out all the wires, and make sure they go to the
correct places. Attach a photo of your magneto to your
posting if you want us to look it over.

The first thing to check are the ignition points. Remove
the wires from the ignition points. Connect your
ohmmeter's + probe to the points terminal, and ground the -
probe. Opening the points with your finger should give
infinite resistance. Closing them should give 0
(definitely less than 1) ohms. If the you're not getting
very close to 0 ohms, your should carefully file the point
faces until it does. The metal seems to oxidize over time.

To test the condensor, you need an old-fashioned analog
multimeter set to Ohms. First touch the condensor wire to
its case to discharge it. Now connect the + probe to the
wire end, and - probe to ground. The needle should swing
towards 0, then immediately reverse direction and head
towards infinity. Leave the probes connected for 15
seconds to charge the condensor. Now reverse the probes.
Again, the needle should swing towards 0 and then return to
infinity. If you get no swing, it's time for a new

Digital multimeters won't work, so you'll need to swap out
the condensor. Just about any condensor from the auto
parts store will work for testing - they're all about the
same capacitance.

If we're good so far, test the external coil and spark
plug, using your wires with alligator lips. Remove the
wires from the external coil. Jumper the - side of the
coil to ground. Hook the - side of a 6v battery to ground.
Lay the spark plug on the cylinder head. Now momentarily
touch the + side of the battery to the + side of the coil.
The spark plug should fire as you disconnect the wire.

Still good? Now it's time to test the magneto coils.
Remove them from the bike, and remember which one went
where. Test each one with your ohmmeter. It the ohmmeter
reads infinity, the coil has a open, and will need to be
replaced. If the ohmmeter reads 0, the coil has a short,
and will need to be replaced. I can't remember the proper
reading right now, but it's pretty low, less than 1 ohm if
I remember correctly. Test both coils, and compare the
readings - they should be about the same. You can also
test them by hooking them up to a 6v battery and taillight
bulb. The bulb should glow about the same on both of them.

The last possible thing to go wrong is the rotor. The
manual says "in rare instances, the magnets may become
demagnetized, through careless handling, careless storage,
or naturally through years of service". The rotor is
probably not your problem.

If you need points, condensor, coils, etc. try Duane
Taylor,, J&M Collectibles - check the
Parts section for contact info.

You can get a copy of the Service Manual at your local
Harley dealer. Ask for Part# 99444-93 "1958-1966
American-Made Lightweights". About $40. Your dealer may
not stock them, but can get one in about a week. This book
has a parts catalog, a service manual, and a ton of other

You can get a dedicated condensor tester from Amazon for
about $20. But you'll probably use it about once every 10
years, so it's not worth it unless you fool around with a
lot of old condensors.


I'm new to magnetos and cant get any spark to the
points. everything looks like new and is very clean. i
adjusted the points to 20% and tested both coils. still 0
spark. any help would be great. john cross

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