Topic: Coil Resistance?

[Fartyboy]

Anyone know what the coil resistance should be on a CB750K8?  From all the posts, I'm going to guess 5 ohms?  With aftermarket coils going down to 3 ohms?

Now, if you'll excuse my ignorance of the multimeter... I took a reading of the resistance of each coil, but could only get a reading when it was switched to "20M" on the meter... and it read between 15-17.

Obviously the difference between the different settings is a matter of a decimal point, but I'm not sure which setting it should be on... 200, 2k, 20k or 20M?

So, my question is REALLY:  Are my coils bad?

Thanks,
Tim

[cbjunkie]

timely post for me, farty - i'm gonna keep watch on this one til TT weighs in...

[eldar]

If I had to guess, you tested the secondary resistance and not the primary.
I have never actually tested mine so I am unsure. The number sounds in the ballpark for the secondaries but I cant remember.

[Fartyboy]

Secondary?  I only have four wires attached to the coils (besides the spark plug wires)... one in the front of each coil (which I assumed were positive), and one in the back of each (I assumed negative).  How would the primary resistance be found?

Thanks,
Tim

[eldar]

Well I have never done it. Each coil has a primary and secondary winding. That is how the voltage is changed from 12v to whatever it is that goes to the plugs.

[malcolmgb]

The primary are the 2 thinner wires, usually about 5 ohms on std coils.
The secondary are the HT cables to the spark plugs, the resistance varies according to the type of cable, resistive carbon or copper wire, also the longer the cable the greater the resistance, then the plug cap may also have a resistor inside. Again std measured from the end of 1 lead through coil to other lead is usually approx 15K/ohm without caps I believe.
If you had meter set on 20M and it read 15-17 then that suggests 15-17M/ohms which suggests a very high resistance.
This is my understanding.

[TwoTired]

Each coil has a black wire and either yellow or blue wire  These are the primary windings.  Stock coils measure in the vicinity of 5 Ohms plus or minus 0.5 ohms.


There are a lot of different multimeters out there.  You should probably post a pic or at least a brand and model number.
However, in general, you usually use the lowest resistance scale available on the meter for this test.  20 Meg ohms is 20 million ohms.  5 is pretty low on that scale.  This is kinda like trying to count rocks in a moon crater with your binoculars.  
For measuring the primary, I would use your 200 scale of resistance.
If you want accuracy, either zero your meter (if it has an adjustment) after putting the probe tips together, or note the reading on the scale and subtract that reading from subsequent measurements on that scale setting.

Make your measurement again and report back.

There is also a test process in the FAQ.  Search for "gazintas" or "gazoutas".

Cheers,

[cbjunkie]

see. good things come to those who wait. 

thanks TT

[Fartyboy]

Okee-doh-kee...

pulled out the wires and tested them on the 200 level... got a 4.8 and a 4.6... so that hints that the coil is fine, right?

Now, the problem is that I have a weak spark, so now what do I do?  I can't check the resistance on the sparkplug wires like I would on a car because there is only one exposed end--the plug end... so how do I know if the wires are bad or not?  And if that isn't the issue, what else could it be?

I have a new battery and new sparkplugs, btw.

Thanks again (I'm gettin' there.

Tim

[Bob Wessner]

Perhaps the plug end of the wires are corroded, which would increase the resistance and demish the spark. Unscrew the plug caps from the wires, snip about an 1/8th in. off the end and screw the plug cap back on, it might help. Also assuming the correct plugs with proper gap and the points are set to spec.

[TwoTired]

pulled out the wires and tested them on the 200 level... got a 4.8 and a 4.6... so that hints that the coil is fine, right?

The primary is.

Now, the problem is that I have a weak spark, so now what do I do?  I can't check the resistance on the sparkplug wires like I would on a car because there is only one exposed end--the plug end... so how do I know if the wires are bad or not?  And if that isn't the issue, what else could it be?

How do you know you have weak spark?
The two fat wires (to spark plugs) is your secondary.  Unscrew the Spark plug boots and measure across the two wires. The wires are all solid core.
Check the spark plug cap resistance terminal to terminal.  S/b 5k-10K.

http://www.sohc4.us/forums/index.php?topic=5752.msg8383#msg8383

I have a new battery and new sparkplugs, btw.

What are your spark plug numbers?