Urgent

[DMPLATT]

Sorry to be so helpless here. I posted about losing 2 cylinders on the way to work this morning.

Now I'm kinda stuck. I got a multi meter and pulled the coils. I got about 4 ohms on the primary on both. However, on the suspect coil I got like 1600 mega ohms on the secondary. So I pulled the plug caps and I get 15k ohms without the caps. I measured both plug caps and 1 I get like 9 ohms, but the other one seems to be dead open. I can't get any reading on it. So I'm going to have the wife come and see if I can find a cap somewhere. And hope that I just didn't have one of the plugs grounded good enough. I only got spark on #3, but not #1 and #4. #1 is the one with the bad cap.

2 problems.
1. I've checked before and the bike shops don't have my caps in stock. Can I use an automotive cap? Or what resistance and so on do I need?

2. Of course with my tank off I collected a crowd of co-workers and while I was taking the wires off the back of the coils, 2 are almost the same color and I can't remember which is which. Is this a problem? Is there polarity? I know the one wire has 12v and I assume the other is the signal? Can someone tell me which connector the 12v goes to?

Sorry to sound so urgent here, but I don't really want to leave the bike if I don't have to.

Thanks so much.

[DMPLATT]

Also, if a coil has 1 bad plug cap, would it still fire on the other cylinder?

[Dink]

orange/white wire goes to the positiive terminal.
You need a resistor cap any will do.
it should spark one cap even if the other is no good
Dink

[Anonymous]

You can use any resistor plug cap that fits.
If one plug cap is bad, the other spark plug would still spark.

Orange/white is the positive lead for both coils.

From my GS850: black/yellow goes to the coil for cylinder #2 and #3, the other one to #1 and #4.

[earlfor]

Re: Urgent

Dave, the 12volt power input (supply) to your coils should be an orange/white wire. Those wires are just a "Y" from the harness and are the same. It makes no difference which coil is powered by which orange/white wire. The negative side of the coils have different color wires. The negative wires from the coils are solid black and solid white.
The negative wires run to the ignition under the right crankshaft end cap.
Usually, the black wire goes to the left coil (cylinders 1 and 4) and is connected to the left sensor on the crankshaft end. The white wire goes to the right coil neg and is connected to the right sensor on the crankshaft end (2 and 3 cylinders). Sometimes though, people in working on a bike assemble things with the black and white wires reversed to the sensors.
As long as the left sensor is wired to the left coil, color does not matter.
You might want to remove the cover on the right crankshaft end to check which color is on which side.

Any resistance on the coils between the + and - terminals between 2 and 5 ohms is within specs. (coils must be unpowered when this test is done)

The resistance on your spark plug caps is 5K ohms. You can use any 5k ohm cap that can be screwed onto your plug wire ends.

Also, check you spark plug wire ends when you have the caps off to see that there is indeed core at the end of the wire to contact the plug cap screw/fitting.

The resistance between the plug caps on each coil (everything, plug caps etc in place) should be between 30K and 50K ohms.

Earl

Sorry to be so helpless here. I posted about losing 2 cylinders on the way to work this morning.

Now I'm kinda stuck. I got a multi meter and pulled the coils. I got about 4 ohms on the primary on both. However, on the suspect coil I got like 1600 mega ohms on the secondary. So I pulled the plug caps and I get 15k ohms without the caps. I measured both plug caps and 1 I get like 9 ohms, but the other one seems to be dead open. I can't get any reading on it. So I'm going to have the wife come and see if I can find a cap somewhere. And hope that I just didn't have one of the plugs grounded good enough. I only got spark on #3, but not #1 and #4. #1 is the one with the bad cap.

2 problems.
1. I've checked before and the bike shops don't have my caps in stock. Can I use an automotive cap? Or what resistance and so on do I need?

2. Of course with my tank off I collected a crowd of co-workers and while I was taking the wires off the back of the coils, 2 are almost the same color and I can't remember which is which. Is this a problem? Is there polarity? I know the one wire has 12v and I assume the other is the signal? Can someone tell me which connector the 12v goes to?

Sorry to sound so urgent here, but I don't really want to leave the bike if I don't have to.

Thanks so much.

[earlfor]

Yes, the other cylinder would still fire.

Earl

Also, if a coil has 1 bad plug cap, would it still fire on the other cylinder?

[Anonymous]

Re: Urgent

Usually, the black wire goes to the left coil (cylinders 1 and 4) and is connected to the left sensor on the crankshaft end. The white wire goes to the right coil neg and is connected to the right sensor on the crankshaft end (2 and 3 cylinders).

This might get confusing. The schematic of a GS850 (electronic ignition) says the opposite....

[DMPLATT]

Thanks for the replies.

I found the 2x 12v lines and put them on the + terminal of the coils. I didn't see the markings on the coils before.
So that should be well.
Of course the Motorcycle shops don't have the caps and closed at 6:00.
The auto stores say they don't have the screw in kind. :?

Also, check you spark plug wire ends when you have the caps off to see that there is indeed core at the end of the wire to contact the plug cap screw/fitting.

Yes I did that, and I trimed about 1/4" and re-checked and still some mega ohms. That 1 cap seems to be bad.

So, I have about 4 ohms on both coils. I have right at 35k on the good coil between the caps.
On the coil with the bad cap I get 15k with out the caps on, I get about 25k with the one cap on and like 1600 mega ohms with the other cap. THe one cap measures about 9 ohms. So I guess that one is gone too? Would that be enough to keep that plug from firing? Also, I'm assuming here then that the coil is probably ok, just bad caps?

Thanks a bunch for the help. It looks like I may have to try and limp it home. Or stay the night at work. :?

[DMPLATT]

Re: Urgent

Usually, the black wire goes to the left coil (cylinders 1 and 4) and is connected to the left sensor on the crankshaft end. The white wire goes to the right coil neg and is connected to the right sensor on the crankshaft end (2 and 3 cylinders).

This might get confusing. The schematic of a GS850 (electronic ignition) says the opposite....

I had the 2 wires from each coil together, I just didn't see the markings on the back of the coil. I also wasn't sure which terminal the wire with the 12v went to. I found it in another thread. So I should be ok there.

Has anyone else ever had a plug cap just fry like this? Seems strange?

[Anonymous]

It's very rare, but it happens.

In case of emergency, you could just strip the high voltage wire an inch or so and wrap the copper core onto the top of the spark plug.
We used to do that "in the old days" and it always worked.
It will get you home. It shouldn't be raining though...

Oh, found a schematic of an 85 GS750. Black/yellow goes to coil for plug #2 and #3.

[RacingJake]

Make sure you got fuel first.

No spark on 1-4 or 2-3 could mean bad coil, bad ignition, open or short on that side of the wiring. Even a corroded kill switch can cause problems with low voltage to the coils.

Best bet is to trailer it home where you can take your time to troubleshoot it.

[DMPLATT]

Thanks for all the help.
I made it home. I managed to fix the #4 spark, actually got a zap too. 8O So I was at least running on 3, instead of 2. :?

I had bought a plug cap a while ago while at the parts store, they only had the 90deg short one. I was sure it wouldn't have worked but it was only a couple bucks so I just bought one.
When I got home tonight I put it on the wire that had the bad cap, low and behold - A nice blue spark.

Anyway, thanks again for all the help. Hated being stuck at work, but THANK GOD FOR THE GSR. You guys ROCK.

[Anonymous]

Is there any reason for resistor spark plug caps, except for minimizing static on am radios that may be near by? You can screw the inside out of the spark plug cap, remove the resistor a replace it witha piece of 10 ga copper wire the same leingth as the resistor, screw the inside back in the cap & you have a non resistor cap, that will never go bad. We did this to a lot of GS's back in the GS era & never had any problems, except for the static imposed on a radio if there was one close by.