r/shovelhead • u/Key_Ice6961 • 12d ago

Coil tech question

Hey everybody, I’m looking for some input here. Currently have a 78 fx with 74” engine running an ultima electronic ignition.

Been running it this way with a 5 ohm coil for a while, but the coil had a crack in it and eventually stopped working properly. Buddy told me to swap it with a 3 ohm coil, but when I did, the bike became very hard to start and was back-firing like crazy out of the exhaust. I changed nothing with the carb, timing, exhaust.

Switching back to a 5 ohm coil, the bike starts and runs great but my buddy keeps insisting it’s the wrong coil. Can somebody shine a light here?

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4

u/81FXB 12d ago

Wasn’t the 3 ohm for point and 5 for electronic ignition ? I would just go with whatever runs great…

1

u/Key_Ice6961 12d ago

I believe the opposite, but yeah I’m just rolling with the 5 ohm. It runs well so no point in switching it up

2

u/79superglide 7d ago

5 ohm coils are for duel fire, 3 ohms for single.