Replace Ignition Coils on Any Seventies Honda Four

| 12/17/2013 4:41:00 PM

Stock coil next to the replacement coil at right

When it comes to motorcycle repair, most of us prefer to stay away from electrical problems — and for good reason. Without the benefit of proper diagnostic tools and experience, tracing electrical shorts and other electrical equipment problems can be difficult.

But that shouldn't stop you from at least trying to suss out some electrical problems, because every now and then you get off easy, like we did recently with a friend's 1972 Honda CB750. The owner had been trying, without success, to track down the source of an intermittent running problem — typically the worst kind of problem to track because, well, it's intermittent. In this case the bike would mostly run perfectly, but then it would misfire, acting like it had one or maybe two cylinders cutting out.

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A quick inspection showed fuel flow to be OK, and the ignition timing was spot on, but when we went to inspect the spark plugs the no. 1 and no. 3 spark plug caps literally fell off the plug leads after we disconnected them from the spark plugs. Looking at the plug leads, we could see that the wires inside the lead were stressed and breaking off inside the insulation. Problem found.

7/11/2018 1:26:04 PM

Very helpful article, doing a similar thing with a '76 cb400. When buying modern coils what ohm is appropriate for a 4 cylinder 70s bike? Seen ones from 3 to 5, but can't figure out which is best suited.

1/16/2014 11:52:58 AM

You can usually just use your old coil and wires by trimming the end of the old wire back a half inch or so and find fresh copper wire to screw into.

Steve Seiwald
12/19/2013 10:20:05 AM

Great article but that first pic is like seeing grandpa in a dress.