CB750 Ignition Coil Test Problems

I know there's a method of testing the coils without the multimeter but I've heard that there many components that cause an inaccurate diagnosis. So far I did the basic test of starting the bike with the spark plugs off & grounded to the exterior of the engine. So I'd receive at least little to no sparks from the plugs. I've also ran the multimeter test through the primary to which I receive 5.0 ohms at 200 but on the secondary side at 20k produces no result. I figure it might possibly be just the coil wire or the boot itself. It it possible that I could change out the wire & replace them with new rather than having to replace the whole coil set itself.

Any feed back would be great, thanks.

With a 4 cylinder motor or a twin with single coil, it is important to ground both sides of teh coil when testing for spark. The motor does not need to be running - It's enough to spin it over a few times.

On a double ended coil the test is from one plug cap to the other. If the values are much above 20-30K ohms, pull the plug caps off and test again. Caps break down and oxidize over time. The ends of plug wires also deteriorate over time and often there is no metal left where the cap screws in. If you have enough lead, trim them back by 1/4" to get fresh steel/copper for tho cap to bite into.

is it possible to replace the whole lead with a new lead if I cut it too short?

Which CB750, and do you have resistor caps? The caps can go bad. I just had to replace all four on a 1978 CB750f. You should definitely test the resistor caps, if you have them.

When I check my primary i get around 4.7 ohms at 200 on both coils. Secondary testing on both coils: Coil 1- 13.90 @20K ohms & Coil 2 - 15.20 @ 20K ohms. Are those readings normal? I guess if I don't get any readings with the resistor caps, it's probably what's causing the problem?

Jrperida said:

When I check my primary i get around 4.7 ohms at 200 on both coils. Secondary testing on both coils: Coil 1- 13.90 @20K ohms & Coil 2 - 15.20 @ 20K ohms. Are those readings normal? I guess if I don't get any readings with the resistor caps, it's probably what's causing the problem?

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Yeah, if you get no reading through your caps, then they're bad. They will also increase in resistance as they go bad.