1970 Norton- testing coils... no spark at plugs

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Is your battery charged?
Is your wiring correct?
Are your plug wires ok?

Test resistance with plugs uncapped. You can also check with a test light with battery connected.
 
Disconnect the existing primary wiring from each coil.
Set your MM to most sensitive scale.
Measure Ohms.
Should be equal.

Slick
 
There are various electrical tests, including coil primary windings, detailed in the workshop manual. It can be found under the Technical Information sticky thread of the forum.
 
Primary coil wiring is the low voltage wiring that is interrupted by the points. This wiring is mostly external to the coil. The primary wiring inside the coil is the object of the Ohm test with the multi meter. If there is a break inside the coil, the Ohm reading will be infinitely high, and no high voltage will occur (no spark).

Secondary wiring is inside the coil and produces the high voltage that causes the spark. The fat wire terminating at the spark plug is the end of the secondary wiring.
 
Are you testing them because there is no spark at the plugs if you remove the plugs, lay them on the head where the plug screws in, reconnect the lead, turn on the ignition and kick the start lever?

That should be your first test - to see if there IS spark. If there is a blue-white spark, no reason to further test the coils
 
MexicoMike said:
Are you testing them because there is no spark at the plugs if you remove the plugs, lay them on the head where the plug screws in, reconnect the lead, turn on the ignition and kick the start lever?

That should be your first test - to see if there IS spark. If there is a blue-white spark, no reason to further test the coils
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Did that. Nothing. Coils are 50 years old.
 
okwebb said:
Did that. Nothing. Coils are 50 years old.
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It still might be something other than coils. My '74 original lucas coils still fine. You could have an issue with the points or condenser or ign power or grounding.
 
okwebb said:
I have a multimeter. Want to test my coils. Advice?
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If you have OEM Lucas coils they are marked on the bottom Either 17M 6 for 6 volt coils used on late bikes with a ballast resistor. or 17M12 for 12 volt coils used on early ( Pre 1972 bikes)

If you hook up a multi meter leads to the two terminals on top of your coil and set the meter to ohms . You should get approx.

2.5 ohms on a 6 volt coil and approx 4 .5 ohms on a 12 volt coil.

*** If you have a points ignition the point contact faces must be clean and oil free.

And then if one of the sets of points is closed and you have a spark plug hooked up to the coil, it and it is well grounded to the head, IF you open that set of points with a small screw driver with the ignition on , IT should cause the spark plug to fire, IF your coil is good and you are getting voltage to the ignition system. (meaning coils and points).

Because a stock OEM bike is positive earth, The battery + terminal is earthed (grounded) to the frame. The battery - is usually fused and IS not used as the ground, but goes to power the ignition switch and lights

The coil's + side goes to the contact breakers (Point's wires Black white and black yellow) and the coil's - side is fed power by the ignition switch. IF you are a positive earth system.
 
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okwebb said:
And what is primary wiring? I’m a novice.
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Primary wiring is the power supply to both coil negative terminals (for positive earth/ground) from the master switch, which on your '1970' model is normally white (see diagram below).
Assuming it still has its original points/contact breaker ignition and 12V coils, and not electronic ignition (say if it does) then for there to be no spark at either plug suggests a fault in the primary so there's no power to the coils or no engine ground to harness red and battery(+) as it would be unlikely, although not impossible for both coils to be faulty.

1970 Norton- testing coils... no spark at plugs
 
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Take a look at you tube there are many vids for checking coils etc
 
To follow up on Carl's good advice, you can also measure from either terminal to the coil output, where the big wire goes. It should show in the range of 5-8KΩ. Also check from the coil's body to the terminals or the coil output and you should read open. Sometimes the output can be open or the coil's turns are shorted to the body, neither of which are good. Of course these measurements with the coils out of circuit.
 
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