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Discussion Starter #1
Hi All,
I fitted a 123 distributor in my 105 to replace the Bosch points distributor all was going great but it now won’t start fuel ok but while I get spark to the lead ends the plugs don’t seem to spark when the electrode is earthed on the cam cover. Could the coil not be put out enough juice?

thanks Phil
 

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When I first installed my 123 I used the old Marelli coil and it failed soon afterwards.. Put one plug lead into the coil, bypassing the distributor and see if you get sparks. If not, try a new spark plug. If still no sparks then it could be the coil, provided that the 123 and coil are wired correctly.
 

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Discussion Starter #3
Thanks, I just tried the the spark plug connected directly to the coil and the spark is strong but weak once coming through the distributor. Does the coil break down slowly providing a weak spark or does it just completely die?

I have wired the 123 red to coil positive, black to coil negative, blue to earth on the body & green from the ignition switch connected to the coil positive.
Does this seem incorrect?
 

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I only know the two wire 123 distributors but your wiring appears to be good if you get strong sparks from the coil.
Verify that the phasing of the distributor is correct. When #1 cylinder is at TDC on the compression stroke the rotor should be pointing directly at the #1 electrode. Also make sure that the rotor is good and seated properly. Measure the resistance between the button on the center top of the rotor to the electrode on the end. It should be no more than about 5K ohms. Also check that the spring loaded graphite button in the center of the distributor cap is not broken or loose.
 

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Don't the 123 systems recommend their own coils?
They recommend coils with a certain resistance value. So the problem could be that Philyg's old coil has the incorrect resistance.
 

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Yeah, they'll work with any coil with >= 1 Ohm primary resistance

If you're describing the problem and the test results right it does sound like an issue with the cap and/or rotor
 

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I had a similar situation and got some great help from @alfaparticle. I discovered that the issue was my distributor which was a worn out Marelli unit. I replaced it with a 'less worn' distributor and it started. However, I also discovered that the 123 ignition is sensitive to your choice of plug/coil wires. I ended up buying a set of magnacore wires and it has been solid since. (coil is Bosch blue even if I think it would work better with other coils).
 

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If it is making strong sparks with the plug wire inserted into the coil then it is not a coil problem.
 

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Discussion Starter #10
Hi All, thanks for the advice. After going to the store and grabbing new plugs and leads she’s back running again. Thanks all it seems the coil wasn’t the issue but I might get a new one regardless. It is amazing though that the plugs and leads could stop the car dead.
Thanks again Phil
 

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The Pertronix coil is 3 ohms. You will get stronger sparks with a lower resistance coil but you must not go below 1 ohm. The Bosch Red is about 1.3 ohms. The Bosch Blue is 3 ohms makes lower energy sparks than the Bosch Red and it was designed for points distributors. I have posted graphs of energy versus rpm for several different coils and Bosch Blue is the worst of the lot.
 
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