testing coils 81GS1000G

[Guest]

I searched the forum for an answer to this question. No luck, so here it is.

I'm having trouble testing the secondary windings on my coils (81 GS1000G). Primary windings test above 4.5 but below 5 (multimeter set on 200 ohms). Can't get any readings at all for the secondary windings of either coil (multimeter set on 20K). I know at least one of the coils is working because the bike runs. It stalls when I pull either of the leads on cylinders 1 and 4; but the bike does not stall (or run differently in any way) when I pull both leads on 2 and 3 at the same time.

The fact that the bike is only running on 1 and 4 leads me to think there is a problem with the coil for 2 and 3.

Strange thing is that I'm getting spark to all four plugs (laid the plugs on the side of the engine and witnessed a spark). Also, when I pulled the leads by hand with the engine running, no. 3 shocked me numerously and painfully (can't remember if no. 2 did that to me too but don't feel like finding out). Can this have something to do with my problem?

The fact that all the plugs are actually firing makes me think about the carburetors . . . but I want to eliminate electrical first. Am I just getting a weak spark to 2 and 3? Would that be the coil or something else?

First things first . . . how come I can't get a reading on the secondary windings? I'm putting one lead of the multimeter in a lead from the coil and the other lead in the plug boot (meter on 20K). What am I missing?

Thanks in advance for your time and considered reply!

[tom203]

As to first things first.....
On each ignition coil,remove spark plug boots from coil wires, then insert meter probes into the coil wires and measure between them on 20 kohm scale- you'll probably get about 12 kohm reading. The boots give erratic readings due to corrosion.
You got spark on all 4 plugs, but maybe not enough- try cutting back coil wires about 7 mm and reattach boots. Check for signs of fuel on 2 and 3 - in bowls and at plugs. Maybe your carbs' idle circuits are plugged- what maintenance have you done?

[von reckless]

As to first things first.....
On each ignition coil,remove spark plug boots from coil wires, then insert meter probes into the coil wires and measure between them on 20 kohm scale- you'll probably get about 12 kohm reading. The boots give erratic readings due to corrosion.
You got spark on all 4 plugs, but maybe not enough- try cutting back coil wires about 7 mm and reattach boots. Check for signs of fuel on 2 and 3 - in bowls and at plugs. Maybe your carbs' idle circuits are plugged- what maintenance have you done?

bought the bike a year ago. Barn find. Worked on it all winter. Among many other things, I adjusted the valves, cleaned the tank and carbs (replacing all o-rings). New fuel lines. Didn't rebuild the petcock, so some chunks could have come out of there. Bike fired right up and ran great on a 2000km tour. It had a flat spot on acceleration at about 1/4 throttle. I thought this was the result of jetting as PO put on pipes from a GS550 (no idea why). On a cold start the idle was low. I didn't turn it up because it idled just right once warm.

Couple of days ago the bike started backfiring a bit as I descended a hill close to home. Once I pulled into the driveway, the idle was very low, like it was when it was cold . . . but the engine was nice and warm and would normally be idling around 11 or 12. That is when I started pulling leads to find out if everything was firing. I let the bike idle for a minute or a bit less to see if the plugs in 2 and 3 would become wet with fuel. They didn't, but maybe I didn't run the bike long enough. I thought it was more likely a coil than the carbs because cylinders 2 and 3 run off the same coil.

Any thoughts?

I shall shorten the leads and the float bowl as you suggest.

thanks for the suggestions.

[tom203]

Since #2 firing is in doubt, check petcock for correct operation- making sure that fuel ain't leaking down vacuum line and fouling plug especially at low rpm. This would also cause backfiring stuff, since unburned fuel would meet up with hot gases down the pipes. Compare spark strength on 1 and 4 to that of 2 and 3

[von reckless]

As to first things first.....
On each ignition coil,remove spark plug boots from coil wires, then insert meter probes into the coil wires and measure between them on 20 kohm scale- you'll probably get about 12 kohm reading. The boots give erratic readings due to corrosion.
You got spark on all 4 plugs, but maybe not enough- try cutting back coil wires about 7 mm and reattach boots. Check for signs of fuel on 2 and 3 - in bowls and at plugs. Maybe your carbs' idle circuits are plugged- what maintenance have you done?

I removed the boots and clipped the ends of the HT leads. Resistance between the HT leads is 11.75 on 1 and 4 coil and 11.92 on coil 2 and 3 (tester set to 20K). That's close to what you say they should be.

However, the Youtube clips I've watched say I should be testing the secondary windings of the coils by placing one end of the tester in the HT lead of the coil and the other in the connector on the supply side of the coil. Is it enough to test each coil between the HT leads as you suggest and I have done, or should I also be doing it the way it is suggested on Youtube?

If you are interested, this is one of the videos I watched.

http://www.youtube.com/watch?v=rRQ45lT2d3c

One more thing: How does one check the relative strength of the plug spark? All the plugs sparked . . . pretty hard to tell visually whether some of the sparks are stronger than the others. Any suggestions? I can try again and look more closely.

Thanks again. I'll get into looking into carburetion and fuel supply once I have eliminated the electrical.

[koolaid_kid]

Put the bike in the garage where the light is not bright sunlight. Evening works even better. Blue or bright white are good colors. Yellow and red are bad, indicating a weak spark.

[Arthur]

Hi guys,

I join this post because i ha a similar problem, but only on #1.

the thing is, i noticed the #1 exhaust was warming later than the others, so decide to remove the respective coil xuri g the bike runing, and nothing.... tryi g diferent position of the throttle but still nothing. I did the same with the #4 and the engine slowed down when coil removed. ...

i dont understand. ...

[RGM]

You probably just have bad plug leads. There is a resistor in them that can burn out. You can get new leads or remove the resistor and put in a chunk of thick wire or thin rod and then use resistor plugs. Make sure your condensers are good too, they can cause weird problems.

[Arthur]

Tks RGM but i dont understand very well, what is the plug lead?

[von reckless]

Tks RGM but i dont understand very well, what is the plug lead?

Here are the names of the parts: First there are the coils (one coil for a two cylinder engine, two coils for a four cylinder). They are bolted to your frame under the gas tank. They are the size of a medium sized bottle of pills. They are probably white (mine are). Could be black. The "leads" are the thick wires that run from the coils to the spark plugs. The part of the lead that attaches to the plugs are called plug "boots" or "caps". Inside these boots are small resistors. I think RGM is saying these resistors may not be working. He is saying you might be able to fix them, but if you can replace them with new boots, that would probably be better.

The first thing you should do is remove the spark plug from the cylinder, re-attach it to the lead and lay the plug on the engine so the metal part of the plug is touching the engine. With the lights out (or at night), see if the plug is sparking when you run the engine. If the plug is sparking white or blue it is good (as Koolaid sugested below). If it is sparking orange or yellow or not at all, then fix the boot as RGM suggests or replace it if you can get one. To remove the boot from the lead, slide the rubber protector off the boot and up the lead, then unscrew the boot from the lead (do not pull it off).

Good luck.