Another post on coils

[anthony8488]

1982 CB750SC, stock carbs(clean)/jets/airbox. Carpy 4-1 Yoshi exhaust.

Swapped my valve cover and I finished tried to start it up to check for leaks. It started idled about 2 sec and then backfired (sounded like a shotgun). After some forum reading first thing was spark issue, so pulled the coils off the bike and tested them as everything says primary at 200 reading 3.8 for both.

Then on the secondary side is where I am stumped, terminal to terminal (wires removed) reads 17-18k for both. One plug wire(spark plug end) to terminal same reading. Two wires (spark plug ends) I get no reading.

All wires show a reading with just one wire in and the other on the terminal, no sets of wires give me a reading plugged in.

Now if i remove the one cap(brand new NGK's on all four) and test the exposed end I get a good reading.

What is this leading too? The wires by them selves check good, a wire with the new cap checks good, both wires and caps = no reading.

Any help would be appreciated.

[TOOLS1]

To test coils with an Ohm meter, you just need to check for continuity between the two plug wires. Continuity=good. Then check for continuity between the two terminals. Again, continuity=good. I am betting that you either switched some plug wires, or the wires going to the coils while you had the valve cover off. The backfiring means that the engine is out of time.
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[anthony8488]

This is where I am having an issue testing them, if i test one plug wire(and cap) on the secondary and touch the other secondary terminal it reads fine, two plug wires on the secondary I get no reading. I bought new caps since when I originally tested them two wires wouldn't read even after sanding the brass fitting within the caps.

If I have two plug wires on the secondary terminal and take one cap off and then test the exposed end and the cap on the other wire, it reads good. Also all wires checked fine being hooked up one on secondary and touching the other secondary terminal(no wires)

I hopped on here and found a service manual that showed the cylinder order as 1432 (sitting on bike looking down) so I hooked it up left coil T1 to cyl 1, T2 to cyl 4 and right coil T1 to cyl3, T2 to cyle 2.

[shinyribs]

Yep. One coil will fire cylinders 1 & 4, the other fires cylinders 2 & 3. The leads of each coil are reversible. Meaning the wires going from the coil to plugs on each coil aren't plug-specific.

THe coil to fire 2 & 3 needs to be trigger by the pulser with the yellow wire, 1 & 4 fire off the blue wire.

It's goofy, but I remember this by thinking of the the two center cylinders, 2 & 3, as the yoke (like an egg), therefore they are yellow.  Hey...it works lol


In stock form the left coil will fire the outer cylinders (1 & 4), but you may have their physical location swapped by accident. Easy to do. Left and right don't matter, but blue and yellow do.

[anthony8488]

I never figured out why when testing both plug wire ends I never got a reading but I did go recheck my wires and I was the problem, hooked them up wrong initially. Got them wired correctly bike fired right up.

The egg idea is good, something odd enough i'll remember down the road for sure.

Thanks for the quick help!