Coil voltage question...

[Guest]

It was raining like crazy here in CT today, so i thought it was the perfect time to install that coil relay mod everyone here talks about.

I wired it on my "82 GS850GL - I think i did it right, I followed the instructions found here.

BTW - these are the coils that have the 2 leads wired directly into the coil body, then attached to a 2-prong plug.

Sooo... with the key & kill switch on, am I supposed to have 12V at EACH coil? I put a voltmeter across the connector plug on coil 1/4 and it reads 12V. When I check the connector plug on coil 2/3 I get 0.2V; however, if I move the ground from the connector plug to the battey (-) terminal, it also reads 12V, so I know I'm getting power to each coil.

Is this normal? I thought I would have 12V at BOTH coil connector plugs?

What's going on here? I didn't check any voltages first, so maybe it was messed up before. I do have a very sooty #3 plug, but #2 looks good.

Your thoughts & guidance please - thanks,

mike

 

[Guest]

as far as i know the coil voltage at the "hot" wire is constant but the other wire is used as a "trigger" by temporarily closing the circuit
only one trigger wire is open at a time
if you were to rotate the engine 180 deg. you shoud get a reverse of your current readings

 

[Guest]

as far as i know the coil voltage at the "hot" wire is constant but the other wire is used as a "trigger" by temporarily closing the circuit
only one trigger wire is open at a time
if you were to rotate the engine 180 deg. you shoud get a reverse of your current readings

I tried that without sucess, although maybe I didn't actually rotate it 180 deg... I'll try again.

Hope it doesn't rain again, who knows what else I can fix !

I've got a wiring digram, I'm going to track that ground wire and see if I can discover any issues.

Thanks for the suggestion,

Mike

 

[rustybronco]

psyguy is correct.
You will have 12v volts at each coil if the voltage is measured from the plus side of the coil to the negative of the battery. you are measuring the voltage to the coil and the ground that is controlled by the ignitor.

coils operate buy applying a voltage to one side of the coil and grounding the other side, this allows the coils to build up a magnetic field in preparation for the coils
"firing".
the coil fires when the ground is removed and that shows up on that one coil, by your no ground "connection".

 

[Guest]

psyguy is correct.
You will have 12v volts at each coil if the voltage is measured from the plus side of the coil to the negative of the battery. you are measuring the voltage to the coil and the ground that is controlled by the ignitor.

coils operate buy applying a voltage to one side of the coil and grounding the other side, this allows the coils to build up a magnetic field in preparation for the coils
"firing".
the coil fires when the ground is removed and that shows up on that one coil, by your no ground "connection".

So if the engine is rotated, then I should see the voltage at each coil going on & off then, right? I tried that but I'll try it again, just want to verify the electronics are correct after my coil relay mod job !

Thanks for the input...

mike

 

[rustybronco]

So if the engine is rotated, then I should see the voltage at each coil going on & off then, right? I tried that but I'll try it again, just want to verify the electronics are correct after my coil relay mod job !
mike

I don't know if rotating by hand will make a difference. it may not switch the grounds on and off until higher rpms (cranking speeds).

did you try and start it?

was an o-ring damaged upon assembly when you overhauled the carbs? (#3 carb)

 

[trippivot]

yes it is right!

if you want to actually see the power switch on and off at the negative primary lead it is better to use a test light at electric starter cranking speed

the goal is 12 clean volts avoiding resistance from the wiring harness. simple as that.

old contact point systems restrict the coil power down to 9 volts to prevent arcing at the points. (don't do this if you have contact point and capacitor system) electronic ignition systems only

the 3 extra volts will burn your points quickly if the key is left on for more than a few seconds without the engine running.

cleaning all chassis grounds including the coils mounting surface will benefit your desired outcome as well.

 

[Guest]

OK, problem solved!!

Actually, wasn't any problem in the first place, just me not rotating the engine around enough to trigger the other coil.

Hey, it was late last night when I finished up...

And yes, rotating the engine by hand works to check this, just remember to pull the plug wires off first to avoid an unwanted start!

Now that #3 BLACK plug - that's the next thing to trouble shoot. I have the tank off at the moment, so I'll open the carb & see if anything is amiss.

thanks for the help guys!

mike

 

[Nessism]

OK, problem solved!!

Actually, wasn't any problem in the first place, just me not rotating the engine around enough to trigger the other coil.

Hey, it was late last night when I finished up...

And yes, rotating the engine by hand works to check this, just remember to pull the plug wires off first to avoid an unwanted start!

Now that #3 BLACK plug - that's the next thing to trouble shoot. I have the tank off at the moment, so I'll open the carb & see if anything is amiss.

thanks for the help guys!

mike

Did you check the spark plug cap? You can unscrew it from the wire and then check resistance of the cap. Also, check the wire itself where the cap screws in.

Good luck.

 

[Guest]

Did you check the spark plug cap? You can unscrew it from the wire and then check resistance of the cap. Also, check the wire itself where the cap screws in.

Good luck.

I'm doing that now - do you know what the resistance is supposed to be thru the cap?

Also, since I didn't pay attention when I removed the cap guts, whats the order of the bits?

Is it, from the wire:

spring
tiny round contact pad
solid pin
screw connector

That's my guess - is it right?
​

mike

 

[Guest]

do you know what the resistance is supposed to be thru the cap?

3-5 k ohm (i think)

but dont quote me on that!

 

[Guest]

3-5 k ohm (i think)

but dont quote me on that!

Actually, I measured the old stock caps at 8K, and measured 2 brandy new NGK caps at 10K each.

I found that my #1 cap was bad, meaning I couldn't detect any continuity or resistance through it, both before & after cleaning. I had a couple of new NGK caps so I put them on the #1 & #4 wires to balance out the look. The other two "old" caps from #2 & #3 checked out OK, but I trimmed all 4 wires back about 1/4" to make sure the wires were "fresh".

Funny, didn't notice anything funky about the bad cap on #1 previous.:-k

However, after all the electrical stuff has been said & done I STILL have a very black & sooty #3 plug. Checked the slide & jet needle washers on it: all looked good & it operated smoothly in the carb body.

I also performed a compression check (as Chef suggested earlier) - all 4 cylinders were just over 150 psi - pretty happy with that.

Ran out of time & daylight (and motivation) to check the fuel level in #3 per the Suzuki method (as Nessism suggested), but will hopefully get to that tomorrow. I've ruled out anything electrical, so I guess I won't be surprised if it fails the fuel level test.

One last thing I now remember - I didn't use Mikuni jets when I rebuilt the carbs, I used the ones in the K&N rebuild pack (won't buy those again, didn't need hardly any of that stuff). Maybe the one in #3 is screwed up??

Anyway, I guess plug chops are in order to see what circuit is actually running rich.

Regards,

mike