From:Dave Hennessey
Subject:RE: 63 scat no fire Date:Fri Mar 30 16:19:11 2018
Response to:22587

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 clips.

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 condensor.

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 information.

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 530/675-9963

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