Cylinder 4 not firing: ignition coil or petcock issue?

[klylor10]

I'm back for more...

I had this issue about 400 miles ago, and it happened again today: bike loses power, then more power, then in about 400 feet dies and will turn over but not catch. The #4 cylinder seems to not be firing, and while it's possible there's another one that isn't, I think it's just number 4.

both times this has happened the following has fixed it: reconnecting the plug cap on number 4 ignition wire, pulling the gas tank and wiggling the ignition wires where they connect to the coil. I've pulled plugs #1 and #4 and they don't look fouled at all, but on both the left and right coils there appears to be a burned spot from possible overheating where the ignition wire connects (can't post pics from my phone). There's also a small crack in my right ignition coil.

I've heard that a faulty petcock can cause cylinders to do this, but my hunch is that my ignition coils need to be replaced. Would you all agree?

if so, what brand would you recommend for an 82 gs850g? I've heard Dyna is good but can't find the right part for my bike.

[JTGS850GL]

If you have a no start issue, then it's not just the #4 cylinder. You could be loosing both the 1 and 4 cylinders together though. First thing I would do is to verify if you have spark or not. If you have no or very poor spark then it's electrical. If you have a good spark then I'd suspect fuel. All you need to do to verify spark is to carry an extra plug with you. Just unplug one of the plug wires and put it onto the extra plug. Lay the plug on the head and crank it over. You should see a nice bright blue spark. You can move the extra plug from wire to wire to verify spark on each cylinder. This way you don't have to remove any plugs to look for spark.

With that said, if you have a bad coil or want to replace the one with a crack, then you can use any 3 ohm coil. The stock coils are pretty reliable and you can pick them up for cheap.

One other area you might want to take a good close look at is the connectors that the coils plug into. They're notorious for getting corroded and melting. You might also want to check the main harness connectors under the tank. They're bad about melting as well.

[Brendan W]

Have you checked the resistances of the primary and secondary sides of each coil ? Primary about 3-4 Ohm, secondary 15k Ohm with the caps removed. What is the condition of the supply plugs to the coils. They corrode and reduce the voltage seen by the coils.
Coils are generally tough and if the resistances are even the problem probably lies elsewhere.

[klylor10]

Update: I think I'm getting closer to identifying the problem. There have been some new developments, but I want to address what JT and Brendan said first:

I've got spark a solid spark on all cylinders. The input spade connectors on both coils were a bit corroded, so I cleaned them and they are making what I believe to be a good connection. I unfortunately don't have any way to test the resistance where I am now.

Now on to the developments. While #4 wasn't firing when this problem occurred, it seems to be working now. I discovered that my lack of power and low mileage was likely due to running only on 3 cylinders, as cylinder #3 stopped working today, and when I pulled the plug it looks like it has relatively little wear on it, very different from all the other plugs, which all look normal. I noticed a small spot of oil at the point of connection where the #3 exhaust pipe attaches to the head. I think this is unrelated but I thought I would mention it.

Since I've got spark on all cylinders, this leads me to believe that I have a fuel issue. I also noticed that there's a dark spot on the back of my right exhaust, and my #3 exhaust tube has bluing. These all make me feel like maybe cylinder #3 is getting too much gas and not firing.

any thoughts on whether this is the issue and if so, how I might remedy it? I am unfortunately not in a place where I can do any major dismantling.

[klylor10]

Another update:

I am getting gas coming out of the #3 float if I open the drain plug, so I know fuel is in there.

I think it might be a blocked pilot jet, because when I run it with the choke on the #3 pipe gets hot. I'm hearing a bit of backfiring only when I have the choke on.

I'm very nearly on the side of the road, so before I crack open the carbs to check the pilot jet, can someone give me some input/agreement that this might be the issue?

When I do get that pilot jet out, any ideas on how best to clean it? I've got access to a grocery store, and an auto parts store will be open tomorrow.

[Chris]

if you have spark and fuel then check your compression.

[klylor10]

Hey Chris,

Not really sure how I can check compression out here... Maybe I can sweet talk a mechanic into doing it when they're open tomorrow. I checked it 3,500 miles ago and it was 120 on all cylinders. I can't imagine it changed much since then...

[tom203]

Just to clarify...... When you say #3 cylinder you mean the inner one under the throttle handgrip ? #1 being the one under the clutch lever as you sit on bike.

[klylor10]

Tom, yes, the third from the left, under the throttle grip.

[tom203]

Switch the spark leads on 2 and 3 and see if problem moves to 2- maybe it's a plug boot problem, so rule it out. I don't see how a clogged pilot circuit in 3 would effect normal running as badly as you described- though you'd get a poor idle

[JTGS850GL]

Sounds to me like you're due for a complete strip and dip on the carbs. If #3 is blocked then the others are going to be in need as well.

[60ratrod]

klylor if you were closer in the state i'd say bring it over and we can tear into it. I have almost every tool I would need. but if you wanna make the trip north to mt vernon, mi casa es su casa and what not.

[klylor10]

Sorry about formatting, I'm doing all this on my phone.

I swapped the wires for #2 and #3, and the problem didn't shift swap with them, so I am no longer thinking it's an ignition problem, but my coils look really fishy (see these pictures for burned area on outer sides of the coils where #3 and #4 connect

http://imgur.com/8l125ib

http://imgur.com/gy4t6dz

I'm a little bummed to hear that it may not be a coil problem because I spent 130 or so on new Dynatek coils and wires. Can anyone give me some encouraging words about this purchase? I'm thinking that my current coils might be leaking voltage a bit.

i think compression is good, as it sounds normal and even when it's turning over without plug wires attached.

I just did a rebuild of my carbs 4,000 miles ago using carb dip, spray, and an ultrasonic cleaner, so it's sad to think that I may have to do it again. I'm going to attempt leaving them mostly together but dismantling the float bowl on #3 to get to the pilot jet.

any suggestions would be greatly appreciated. Thank you!

[60ratrod]

The dyna coils and wires are a good move. Just be cautious with the bushing spacers cause spark can jump from the connections to the spacers and pop fuses. What i did is i went to ace and bought some nylon bushings to help alleviate that

[klylor10]

The dyna coils and wires are a good move. Just be cautious with the bushing spacers cause spark can jump from the connections to the spacers and pop fuses. What i did is i went to ace and bought some nylon bushings to help alleviate that

Do do you mean get some additional bushings to add more space? Maybe I'll know more when they arrive.


Any chance the problems described could be attributed to a petcock issue? I didn't smell any gas in the vacuum line, the plug didn't look wet, and from my research it's usually cylinder 2 that gets bogged down from the petcock issues.