1982 GS750E Coil trigger drops at temperature:

[MK3Brent]

Greetings!

I figured would move this particular question to this sub-section, as my other question stemmed from my carburetor thread.

What the bike is doing:
Starts, and runs very well.
I can ride for about 10 minutes before I lose 2 cylinders.

What I've done:
Determined that I have lost spark to the coil responsible for cylinders 2 and 3.

I cut the trigger wires, attached bullet connectors, and swapped the trigger wires from coil A to coil B.

The problem follows this approach.

The coil which gets the BLACK/YELLOW trigger will fail to spark after the bike reaches full operating temperature.

Measurements:
I removed the signal generator cover to visually inspect the unit.
Resistance measured between the terminals for the signal generator is: 360Ω.

The service manual says this value should be between the following tolerance: 120-200Ω.

Because of this, I believe my signal generator may be out of spec.
However, I have read in my searches here the resistance measured can be much higher.

I don't know the answer to that.

Shameless plug: If you have some known good replacements for the igniter, and signal generator please PM me!

Thank-you,

 

[shakeybone]

I had a similar problem on my 82 GS650E, after about 10 min I would loose all spark. I did alot of diagnoses like you did and felt that it was the trigger, replaced it and it did the same thing. I replaced everything including the coils with Dynatech and the bike runs better than it ever has.
With my limited knowledge, I believe if you have a mechanical advance it should be an easy install ( if not you must get a mechanical advance ). The only thing I had to do was file down the spacer that came with the kit.

 

[MK3Brent]

I think I'll purchase a new signal generator, and igniter and just replace one at a time.

They're good parts to have spares of.
Just have to find good parts.

 

[mike_of_bbg]

+1 the Dyna S is very reliable and an easy install if you have mechanical advance. It will replace both the ignitor and sig gen. The GSes started getting ignitor advance in 82 on some models, not sure where the 750E falls on that progression. (OK, I just looked at the parts fiche and the 750EZ does use mechanical advance so you should be golden to use the Dyna S DS3-2)

I'd sooner suspect the ignitor. The sig gen has two coils. There are three leads; one for each side coil and the center tap. If you measure across both coils the resistance should be about double what each individual coil would be.

 

[MK3Brent]

+1 the Dyna S is very reliable and an easy install if you have mechanical advance. It will replace both the ignitor and sig gen. The GSes started getting ignitor advance in 82 on some models, not sure where the 750E falls on that progression. (OK, I just looked at the parts fiche and the 750EZ does use mechanical advance so you should be golden to use the Dyna S DS3-2)

I'd sooner suspect the ignitor. The sig gen has two coils. There are three leads; one for each side coil and the center tap. If you measure across both coils the resistance should be about double what each individual coil would be.

Thanks for posting!

How can I determine if I have the mechanical advance version?

I would love to delete the igniter with a unit like this.
I can post some pictures today around 7PM Eastern.

 

[mike_of_bbg]

Well, here's the image from the signal generator fiche for the 82 GS750EZ. The advance mechanism is part #4. If you take the ignition cover off and can turn the rotor about 20 degrees by hand then you have mechanical advance; or just look for the parts down there but it SHOULD be there. The DS3-2 bolts in place of the signal generator (plus it comes with a new rotor), but has the igniter "built in" to the sig gen unit and wires directly to the coils. You should remove or at least unplug your old igniter when installing the Dyna. It seems Dyna's spacer is usually a tad too thick and won't let the rotor advance when the crank bolt is tightened down, so as noted you may need to sand down the rotor top a bit or find a thinner spacer.

Dyna installed:

You should also check your voltage at the coils. While you're re-wiring for the Dyna is as good a time as any to add a coil relay if your coil voltage is significantly below battery voltage.

 

[MK3Brent]

Edit: Nevermind.

I am pretty sure that's exactly what I have.
Same image from the babbits PDF parts sheet.

I'll double check tonight, then order the Dyna unit.

 

[MK3Brent]

I went ahead and ordered the DS3-2, so we'll start there.
I love the idea of deleting the igniter and replacing the signal generator in one step.

Thanks for the recommendation.

 

[MK3Brent]

Here's a brand new Dyna-S
Turns out my black/yellow trigger wire was damaged inside the igniter.
Doesn't matter now, cause the bike runs great with the Dyna.

 

[MK3Brent]

 

[mike_of_bbg]

Good deal. Did you make sure the rotor was still free to advance after you tightened down the crank bolt?

 

[MK3Brent]

Yes.

I don't know if they made a revision to the design, but there's 1/32" gap between the hex washer and the rotor surface.
It's free to move once tightened.

Bike runs like new again.

 

[JEEPRUSTY]

Very nice photo\writeup thanks.

 

[MK3Brent]

I didn't time it yet.
Just matched the angle as close to possible on the stock signal generator, and the bike runs great.