Ignition Coil Identification Help

Hi,
Can anyone help me identify the ignition coils on my bike?
It's a 1981 XJ550
The coils each have the following printed on them:
12v cm12-10 102 4go

The only place I found that referred to "cm12-10" was chacal's post for an XJ900RK. Does that mean my bike has the wrong coils installed? I could not find a part number for the XJ550 coils, so it's hard to confirm.

They both test 3.1 ohms on the primary side and 11k ohms on the secondary. I was surprised that 3.1 ohms was out-of-spec, and that both were testing the same amount out-of-spec. Maybe that means that I'm referring to the wrong spec?

I'm thinking that I need new coils (and the correct type this time), but I wanted to see if anyone disagreed.

 

Hi Absolin,
Since your results were the same from both coils I would check your meter.

Make sure you are getting a true 0Ohm reading on a dead short of the leads or try another meter before going out and purchasing new coils.

Also check where you are testing from, the end of the primary side wire or the point that the wire attaches to the coil, is in good condition.

The extra resistance could just be a corrosion error or meter calibration error.

I would expect the coils to be close to open or a dead short but not as close to the mark as what you are seeing, on the primary side at any rate.

 

Thanks cds, I'll recheck my calibration, and also try with another multimeter.

I checked the 1/4 coil where the wires connect to the coil, but I checked the 2/3 coil on the relay (the white plastic box that hooks up to the rest of the bike - that's relay, right?). Before getting new coils I'll pull it off and check right on the solder points on the coil.

 

I rechecked. If I dig the tips of the multimeter into the solder, the resistance goes down to 2.9.
When I touch the tips of the multimeter together, the reading is 0.5

I guess that means my coils are fine, I'll assume that 12v cm12-10 102 4go is the right part #.

Though my multimeter may not be - it's digital so I don't believe there is a way to calibrate it.

 

Well the reading sounds good now! Good one!

Sorry I have no idea about the ID on the coils but since it seems most of the TCI's may have common output currents with timing variations only on a sub-board within the unit, so it would look pretty good as a swappable component between capacities and years.

Not sure about the white plastic box either... whack a pic of it up, so we can see though!

It's the other side(secondary), with the screw on plug caps, that gave me most of my ignition problems at the beginning of my project.
Water ingress and corrosion played havoc with those connections so much that I shortened the leads a centimetre or so to get some fresh copper to screw into.

 

The plug caps screw onto the wires, and the resistor cores screw into the plug caps. I've had both come loose and drive me crazy overlooking the obvious.

If they're OE Yamaha coils, highly unlikely they're the wrong ones (of course anything's possible)

From chacal's catalog:

HCP420 OEM factory IGNITION COIL fits both the #1/#4 and #2/#3 cylinders. NOTE: originally, there were two separate coils that differed only in the length of their spark plug lead wires (the #1/#4 coil had longer wires) and the color of the wire on the primary input. These HCP420 original coils are now only available in the "longer wire" version, and will work as either a #1/#4 coil or a #2/#3 coil. Electrical specs are as follows: 2.8 - 3.0 ohms on the primary side, and approximately 13K ohms on the secondary side. Fits all XJ550, XJ650, XJ750, XJ900, and XJ1100 models. Each:
$ 109.00

HCP420SET2 OEM factory IGNITION COILS set of 2.
$ 195.00

And to confirm your coils: The "4G0" part number is your confirmation. "4G0" is the model number prefix of the original XJ400, and is found on many parts on the 550s. (Look at the inside of your alternator or clutch covers.)

The Yamaha part numbers for the coils (and they are still available, I'm showing $127.31 each or more plus OMG to ship) are 4G0-82310-60-00 (L) and 4G0-82320-60-00 (R.) The only difference being the wire lengths, as Len's listing points out.

Yours may be fine however.

 

resolved:
Plug 2 had a corroded wire
Plug 3 had a completely broken cap - resistance of 700ohms (vs 5ohm spec)

Running MUCH better now. 2 & 3 must have been firing occasionally, I was riding around mostly fine, the bike just felt a little underpowered and sounded inconsistent.


Also, I found that the diaphragm on my petcock needs to be replaced - I originally started to look into this because of a hard start.

 

Absolin, On a digital multimeter when you touch the probes together you said your meter said .5 ohms. THAT is your calibration. when you take your reading on the primary or secondary SUBTRACT the .5 from the reading you get and thats your measurement. Mine was .4 calibration and my measurement was 3.1 soo 3.1-.4 =2.7..right on the money