Mikesxs stock coil replacement connections

79josh81

XS650 Addict
Messages
427
Reaction score
419
Points
63
Location
Kiel, Wisconsin
So I ordered two replacement coils from mikesxs (the ones for the original points system). I went to swap them in and noticed that the male and female terminals are swapped on the wire colors compared to the stock coils. Will they work normal if I hook them up how they are? Or do I have to rewire the connectors (which would be lame).

I tried searching the forums for the answer and found some insight but I’m still confused as to whether they’ll work fine the way they are. I’m new to xs650 electrical stuff but I’m trying to understand it better. Any help would be appreciated. Thanks in advance.
 
You'll get spark either way, but here's a pic of the coil wiring.
70-70_CoilWiring.jpg


The proper wiring has the common tie point in the coil going to the points. Backwards wired primaries may cause some points arcing, and unwanted voltage spikes on the power feed line. You'd need to do a few combinations of probes of the coil wires with a good meter to determine this, looking for 8k +/- 4ohms. Don't think a budget meter would be up to the task.

I'd have to think about this awhile to cook-up a definitive test...

Edit: Another, better pic.

70-70_CoilWiring2.jpg
 
Last edited:
Could one tell by where the wires enter the coil? The originals have the orange (points) wire entering closer to the spark plug wire, brown (power) wire farther back .....

PAzSKOS.jpg
 
Thanks for the replies. Well I got the coils in and I'm happy to report everything seems to be running fine. I'm just happy its running at this point to be honest. lol The fact that it's a 40 yr old bike that hasn't ran for over 5 years and a week ago, when I bought it, i poured gas in it and it literally poured out of the petcocks, fuel lines, and carbs. Once I replaced everything there and went through the carbs I figured out it didn't even have spark. So I went through all the electrical and ignition, replaced what needed to be replaced, and the old girl took her first breath in 5 years 30 mins ago. *high five*
 
I think there's only one reasonable way to know -- the leg with the primary would have a slightly higher resistance to the plug wire than the other leg does.

Or -- if you say one way causes more sparking at the points, try connecting it the way that sparks less :)
 
The polarity of the coils primary does matter. It has to do with the polarity of the high voltage to the spark plugs. The convention is to have the voltage to the spark plugs a negative voltage. If the primary wires are reversed, then the high voltage to the spark plugs will be positive, with a few consequences:
1. Timing lights are designed to work with the conventional negative voltage to the spark plug. A positive voltage will cause the timing light to be erratic or not work at all. You can work around this problem by reversing the clamp on the spark plug wire.
2. Spark plugs are designed to work with a negative voltage. The tip of the spark plug gets hotter that the ground electrode to "encourage" the electrons from the negative voltage to jump the gap. A positive voltage on the spark plug center electrode can require as much a 40% higher voltage resulting in poor starting, less power and lower gas mileage.
3. An Iridium spark plug will only provide better power and economy with a negative voltage on the spark plug because the secret to the Iridium is the super hot center electrode encouraging the electrons to jump the gap, allowing for a wider gap. There is zero benefit operating an Iridium plug with a positive voltage.
 
The polarity of the coils primary does matter. It has to do with the polarity of the high voltage to the spark plugs. The convention is to have the voltage to the spark plugs a negative voltage. If the primary wires are reversed, then the high voltage to the spark plugs will be positive, with a few consequences:
1. Timing lights are designed to work with the conventional negative voltage to the spark plug. A positive voltage will cause the timing light to be erratic or not work at all. You can work around this problem by reversing the clamp on the spark plug wire.
2. Spark plugs are designed to work with a negative voltage. The tip of the spark plug gets hotter that the ground electrode to "encourage" the electrons from the negative voltage to jump the gap. A positive voltage on the spark plug center electrode can require as much a 40% higher voltage resulting in poor starting, less power and lower gas mileage.
3. An Iridium spark plug will only provide better power and economy with a negative voltage on the spark plug because the secret to the Iridium is the super hot center electrode encouraging the electrons to jump the gap, allowing for a wider gap. There is zero benefit operating an Iridium plug with a positive voltage.

So are you saying I should rewire the connectors on the coils?
 
How to determine the polarity of your spark plug wire:
If you are uncertain of the polarity of your spark plugs wires, there is a simple way to find out and the only tool you need is a very sharp #2 pencil.
Hold the tip of the pencil between the spark plug wire and the spark plug terminal with the spark plug cap removed.

spark_polarity.gif
If the Voltage is the correct negative voltage, then you will observe a shower of electrons emanating from the tip of the pencil to the spark plug terminal. Just remember that you are fooling with several thousand volts here, so be careful!
Why do this? Because if one or both of your coils are reversed you are not getting the best performance from the engine, even with a points type ignition.
Now, having said all of the above, there is no need for this with a dual output coil because one of the wires to the spark plugs is negative while the other is positive, so nothing can be done about the positive wire except that the typical dual output coil is designed to produce about twice the minimum voltage required in order to overcome the 40% deficit on the positive wire.
 
The polarity of the coils primary does matter. It has to do with the polarity of the high voltage to the spark plugs. The convention is to have the voltage to the spark plugs a negative voltage. If the primary wires are reversed, then the high voltage to the spark plugs will be positive, with a few consequences:
1. Timing lights are designed to work with the conventional negative voltage to the spark plug. A positive voltage will cause the timing light to be erratic or not work at all. You can work around this problem by reversing the clamp on the spark plug wire.
2. Spark plugs are designed to work with a negative voltage. The tip of the spark plug gets hotter that the ground electrode to "encourage" the electrons from the negative voltage to jump the gap. A positive voltage on the spark plug center electrode can require as much a 40% higher voltage resulting in poor starting, less power and lower gas mileage.
3. An Iridium spark plug will only provide better power and economy with a negative voltage on the spark plug because the secret to the Iridium is the super hot center electrode encouraging the electrons to jump the gap, allowing for a wider gap. There is zero benefit operating an Iridium plug with a positive voltage.
 
On a 4 cylinder magneto such as the Slicks on Lycomings, 2 plugs fire positive and 2 fire negative. All 4 put out the same power. Every 100 hrs, you rotate the plugs to even out tip erosion. It's worked that way for goin' on 80 yrs. Just sayin'..... ;)
 
On a 4 cylinder magneto such as the Slicks on Lycomings, 2 plugs fire positive and 2 fire negative. All 4 put out the same power. Every 100 hrs, you rotate the plugs to even out tip erosion. It's worked that way for goin' on 80 yrs. Just sayin'..... ;)
Is it also true that the four wires from the magneto are distributed with two on the top spark plug of two of the cylinders and two on the bottom of the other two cylinders and that there are two magnetos with similar wiring and that they are arranged to complement the other magneto so that each cylinder has one spark plug with a negative voltage to one of the two spark plugs?
 
Is it also true that the four wires from the magneto are distributed with two on the top spark plug of two of the cylinders and two on the bottom of the other two cylinders and that there are two magnetos with similar wiring and that they are arranged to complement the other magneto so that each cylinder has one spark plug with a negative voltage to one of the two spark plugs?
It is..... and it's also true that the engine will still make rated take-off power with one mag. inop... or just shut down. You'll get an rpm drop of about a hundred revs. And that's mainly due to the single flame front moving across the piston vs. two fronts burning towards the middle with two plugs. Not really much to do with polarity.
 
Back
Top