Noob with coil issues

M

Mags

Active Member
Well today I finally put the bike back together (1980 cb750k) and now I don't have any spark. Tested this with the plug in the boot while cranking the stater, whilst holding the plug close to the engine itself. No spark. After close examining, I saw that one of my coils is cracked. That being said, I have no idea where to purchase a new set of coils and plug wires. Could someone please point me in the correct direction? The only thing that keeps popping up is sohc cb750s.

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To update I checked the connector of the coils and they're reading 2.8 and 2.6 ohms. However testing the plug ends resulted in absolutely nothing.

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Most suppliers will carry the coils you need. Additionally the factory coils from a mid-90's CBR600 will also work for you and will allow you to acquire used parts and save some money, while getting a performance advantage. Used coils can be found at any local wreckers, eBay, Craigslist or whichever classified ad service you prefer.
Also, checking the coils involves connecting an ohm meter across the primary (low voltage) terminals. You should have 3 ohms (more and it's open, less and it's shorted). There is no real test for checking the secondary (high voltage) side that I'm aware of; but I'd assume open circuit is normal, otherwise the field would never collapse.
 
Thank you for the reply. I've ordered a new set of coils from deadbeat customs. I figure I might as well replace it since one of them is cracked.
 
They are double lead coils, yes? To check the high tension leads, check resistance between the two plug leads on one coil. You should get a reading of 12-15k. I had the same problem on my GS, and had actually bought new coils on eBay only to find out that those were dead and the originals were still good.

If you had spark before you rebuilt, it's likely a culprit other than the coils. They don't usually just die unless you leave the key on overnight.


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advCo said:
They are double lead coils, yes? To check the high tension leads, check resistance between the two plug leads on one coil. You should get a reading of 12-15k. I had the same problem on my GS, and had actually bought new coils on eBay only to find out that those were dead and the originals were still good.

If you had spark before you rebuilt, it's likely a culprit other than the coils. They don't usually just die unless you leave the key on overnight.


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Click to expand...

Sorry I'm not very familiar with electrical work so I'm learning a ton on the way. So I've probed the pig connectors on the coils and im getting power there. After leaving one of the probes in the connector, I put another probe into the spark plug boot and no power. If im not mistaken this is the correct way to check the secondary on coils? Anyway I've ordered a set since both coils are cracked. I'm pretty stumped as to why I'm not getting spark though, I did unplug the entire harness in order to remove the battery tray. Everything is plugged back in but...no dice.
 
Ignore the small positive and negative wires for now. Put your multimeter on 20k ohms and put the negative inside one spark plug boot, and the positive inside the other spark plug boot. That should give you a reading.

Better yet, snip off the very end of each spark plug lead, then push the probes right into the wire, that way you'll get an accurate reading.

You can screw them back on again after and it always helps to have a fresh bite of cable.

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advCo said:
Ignore the small positive and negative wires for now. Put your multimeter on 20k ohms and put the negative inside one spark plug boot, and the positive inside the other spark plug boot. That should give you a reading.

Better yet, snip off the very end of each spark plug lead, then push the probes right into the wire, that way you'll get an accurate reading.

You can screw them back on again after and it always helps to have a fresh bite of cable.

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Click to expand...

Will be doing this soon. Thank you for dumbing it down for me man.
 
If that nubbin is what you're referring to, my understanding is that it's purpose it to prevent the switch set from moving/rotating on the bar.
 
Ok that's what I figured. I thought maybe it was a form of ground.

So what I've gathered is, I'm getting power to one coil. I know for sure my starter solenoid is bad but I'm jumping the terminals to rotate the stater in order to check for spark, of which I do not have.

I've bypassed the kills witch (by connecting the two wires together)
I've also connected the red and black wires together on the ignition switch.

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Sounds like a bad connection or a shorted wire somewhere. Spark on both all 4 or just power to the coils?


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Nice job, Mags; congratulations!
advCo said:
Sounds like a bad connection or a shorted wire somewhere.
Click to expand...
Yup. It's a 35 year old bike. Check and clean all your connections. You want shiny, clean metal and good drag on the pins
 
I haven't checked if I'm getting spark on all cylienders, it does run terrible and it's a bit difficult to start. I'm guessing I'm running on 2 cylinders.

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