'79 GS850G no spark cylinder #2

[svahnm]

I noticed that cylinder #2 is not working properly and my GS850g is running with 3 cylinders. I changed spark plugs. I tested compression it was 125psi like others too (one 130psi). I tried to spray extra fuel to carburetor no.2 no difference. Spark seems to be allright on all cylinders when plugs grounded outside. When running normally no.2 seems to die totally. Arc from spark plug wires are about 10mm at least. Breaker points are good.

I have tested to swap coils, condensers, wires, boots and problem stays always on cylinder #2. Then I removed 1 and 4 plugwires and grounded them with extra plugs on the head. Then cylinder #2 started to fire!! Also alone it works without #3, but straight after I attach plugwires #1 or #4 cylinder #2 dies again??? How this is possible? What could be the next step?

[MekaniX]

plug gap maybe ?

Other cylinders could be taking all the energy away from that one cylinder ie: too much gap.

[mark]

I had a similar problem with my '79 850. Check your battery, it needs to be in very good condition. Using an ohmeter check for voltage from the battery to the orange wires that give power to your coils. Shouldn't have much of a drop in voltage....if so, some good connection cleaning is in order. Its important to have more than spark, it needs to be a good spark.

I had a couple of spark plugs that once they were fouled, refused to fire after that, even with cleaning, so have new plugs available. Check for arcing between the points if you still have points ignition. Test your plug caps for proper resistance. Test the primary and secondary wires of the coil for proper resistance (sorry I can't remember the specs on that).

Ultimately after a good cleaning of connections from the starter button on down, I got all four cylinders firing reasonably well. But my plug wires weren't in the greatest shape and I decided to go with a whole new Dyna S ignition.

That solved the problem for good!

[svahnm]

I forgot to mention I reduced plug gap to 0.3mm (#2) and kept others ~ 0.6-0.7mm. I tested three set of new plugs. I used battery charger while starting and running..

Yesterday night I was studying this forum and found out also those orange wires interested to be checked. In the Evening I just didn't get it because by swapping coils didn't move problem to other cylinder group so I thought it too mysterious.. At the end I felt even manuals (haynes,clymer) useless because there was claimed that failure should be pair of cylinders if coil etc...

I have breaker points (visually new looking, going to change them anyway soon) and they both seems to arc a bit, but my father said that much is normal. Is it? While I was slowly turning engine with a wrench they were arcing little. On running I don't remember was there any arc..

So, thanks guys for your advice. I will test battery, voltage (at orange wires), resistance of plug caps and those coils and might test to reduce all plug gaps somewhere 0.3mm..

I will report back after. Thanks.

[svahnm]

Here are some testing again..

1.First cylinders #2&3 orange wire to the coil gave almost 2 volts less than battery voltage. I cleaned connection and now both are same with battery. I tested those wires coils disconnected, other case it drops about 1-2 volt when attached. Is this ok?
2.Resistance of coils are about 4 ohm like manual says.
2.From plug cap to plug cap was about 22K ohm (15K ohm manual), but I would consider them ok, because both circuits gave same resistance (my multimeter is rather cheap).
3.Voltage was about 14V while running over 2000-3000rpm so alternator should work and give enough voltage to coils.
4. Resistance from breaker points up to coils is low so wires aren't damaged.

I realized that cold engine all the 4 cylinder fires but after few minutes number 2 drops away. So it seems to relate to heat? But if I remove 1 and 4 wires and attach them with grounded extra plugs on the head and start engine again, cylinder #2 starts to fire again with cylinder #3 even full hot! How another coil circuit can affect to this? Is there some crossfire possibility?
Yesterday while I was running engine without gas tank on it I heard like electric arc would occur somewhere near wires, or coils. Frequency is quite low, so only about every fifth spark would miss or something. Not sure, but sounded like that. I tried to see it in dark later, but then it didn't occur anymore.

I start to be quite helpless with this. Should I try to change breaker points for 2&3 anyway although another one works also at least for cylinder #3.

[mark]

You should have no arcing between the points....that indicates a bad condensor. Also it is possible for you coils to be good cold and mess up when they get hot......heat can definitely be a factor. Also just because the plugs are firing on the grounded plugs doesn't necessarily mean they are firing in the cylinder plugs.

make sure when you run your engine with the tank off that you plug the vacuum line because if you don't that will mess up your carburetion and cause problems as well.

I get your frustration but have had excatly the same experience.

By the way, is your bike stock? Stock airbox, stock exhaust? Done any carb work?

[SqDancerLynn1]

My advise would be to replace the coils !!!! some arcing is normal for the points !!!!!!!! If they don't arc then you have a problem. My 850 had weak spark, Replaced the points,cond,plugs still wouldn't run.. Turned out the coil were bad even tho it had some spark. When you measurte the voltage on the coils BLOCK the points open with a business card etc. CHECK the ignition switch, my 79GS850 had a high resistance & was loosing voltage thru the switch. You can usually get a used set from a Bandit, RF900, GSX (pre coil on plug) for cheap--just change the plug caps

[svahnm]

mark:

Heat must build up inside coils, because while running without tank failure occurs before coils are exposed to heat from the engine. should I start to play with cold spray...
While running engine, points are not visibly arcing at daylight (at least I didn't notice), but when I turned engine slowly by wrench then arc happened. Must be normal.
Vacuum line was plugged while tank was off.
Bike is stock with all the components. All the components from airbox to mufflers are stock. I bought the bike approximately 2 weeks ago. It was working fine for a test drive (2kms), but maybe cold weather or something made failure to postpone enough..

SqDancerLynn1:

Then both of the coils should be failing? Changing wires to another coil won't move failure another cylinder group.

Sorry about my ignorance, but I think I measured coils wrong way?? So, should I check voltage, points blocked and rest of connections attached? So, I measure orange wires near the coils to grounded where? Battery?

Edit:
I was calling around to find new coils, but in Finland it seems difficult to find parts for the bike (except points and condensers). One place stripping parts would have used tested coils for 60 euros per each (about 70-75 dollars). A New part would be starting from one hundred euros if I could find one. Are those spark plug wires possible to change? Those seems to be like glued in coil cover. Is there any change to modify with different kind of coils?

Thanks for your patience!

[mark]

All I can say is that I had the same experience and it got better when I went through the bike and cleaned every connection that I had....starter button, ignition switch, ground wires the whole thing. My points were visibly arcing badly which went away when I put in new condensors. Yours seem normal.

It was crazy. My coils tested O.K., everything tested normal, but spark was erratic, sometimes the coil would only fire one plug. Switching coils didn't do anything. I had plugs that wouldn't fire after they were fouled, put in a new plug and it worked. ](*,)

Finally, after cleaning everthing and installing a new battery and another set of plugs it actually seemed to work O.K., but I have to say the spark always seemed weak.

Three months ago, I decided to dump the whole set up and put in a new Dyna S ignition (about $275 dollars U.S.) including spark plug wires. I got tired of messing with it. Got it in in about 3 hours.

If you would like, I"ll send you my old coils for free and you can mess with them if that might help. One of the plug wires is cracked, electric taped etc. and they are very used, but who knows? They tested normal on my ohmeter. Can't say it will help at all, and it might be just more hassel, but PM me with an address if you are interested.

[svahnm]

Thanks Mark, but it would be far too much to ask you to send them to the Europe... If I end up changing coils I can afford those from that Finnish junk yard if I can't find the new ones or simply upgrade ignition. My bike is classified as museum vehicle, so it is not allowed to modify it a lot. Of course, if it is "invisible" change I can do it. I Should study that Dyna S, because I really like to ride with this bike. My GSX-R and GPZ are out of question if I just feel to cruise around countryside nice sunny day.

Back to problem, I have been reading other posts where Scud had problem with carbs. I started to think again is ANY change that carburetor would cause that (cold working, hot not working cylinder #2). Only what makes me not to consider carburetor is when removing 1# and 4# spark plug leads will make number 2 working also hot. Also tried to spray start spray to the carburetor #2 and no difference at all. Maybe it is just ignition related because compression was adequate too.

I'll be back after doing some more research.

[drcoopster]

Have you tried switching the two coils on your bike to see if the problem moves to a different cylinder? That should tell you if it's a problem with one of the coils. Otherwise it could be a problem with your #2 spark plug wire, it may be shorting to the engine block.

[svahnm]

Have you tried switching the two coils on your bike to see if the problem moves to a different cylinder? That should tell you if it's a problem with one of the coils. Otherwise it could be a problem with your #2 spark plug wire, it may be shorting to the engine block.

Yes, see the first post. Problem stays always #2 spark.

*******
I have tested to swap coils, condensers, wires, boots and problem stays always on cylinder #2. Then I removed 1 and 4 plugwires and grounded them with extra plugs on the head. Then cylinder #2 started to fire!! Also alone it works without #3, but straight after I attach plugwires #1 or #4 cylinder #2 dies again??? How this is possible? What could be the next step?
*******

Yesterday I decided that coils must be working, because failure stays always same cylinder. So it would mean that failure happens before coils. Even breaker points were obviously working for cyl #3 (so should be fine for #2 also), but on the other hand specific spark for combustion stroke for cyl #2 was another cycle than for cyl #3. So every second time #2&3 points opens it would fail somehow and screw the spark for the "dead" cylinder??
I started suspect breaker points anyway.

I tested with lamp to turn engine around slowly. 1&4 points were cutting current for every half turn, but at first 2&3 points seemed to keep contact all the way round. Only some moments little bit cutting current or then it was looking like that when other sparks took energy. I was confused and repeated to rotate slowly and it seemed that it was working unlogically. Some moments it cutted connection, but sometimes felt that light is on too much. Later I tested again and couldn't repeat it anymore.
I adjusted that "non-working" points gap a bit smaller to 0.3mm (before 0.4mm).

I made test ride and again it runs idle fine at first, but when hot #2 is cooler than others and is almost choking engine while idling and power is missing. Anyway after ride I casted some water on the pipes and also #2 boiled away so it must be firing sometimes, even plastic doesn't melt on the pipe like others do.

Please help me, is there any other factor than little lobe in axle pushing breaker points separated while turning engine? How on the earth it was possible that points would keep current flowing even they visible separate each other. Anyway that could be the reason for missing spark. I hope you still follow what I have done and found. Sorry my troubleshooting has been sometimes little bit jumping around. I'll try to be logical.

Today I try to have time to get new points. I need to take my father to help with ignition work.

[flyingace]

All I've seen is attention to the ignition system. From all indications, #2 plug fires OK like the other plugs - right? Is there something I missed in this thread that would eliminate a problem with #2 carb? If I did, just ignore me...

[svahnm]

All I've seen is attention to the ignition system. From all indications, #2 plug fires OK like the other plugs - right? Is there something I missed in this thread that would eliminate a problem with #2 carb? If I did, just ignore me...

My first post: **** I tested compression it was 125psi like others too (one 130psi). I tried to spray extra fuel to carburetor no.2 no difference ****

I actually sprayed start spray. Carb #2 did no difference, but other carbs seemed to choke from extra fuel while idling. Is that reliable test enough? How I should close out carbs? On the other hand it will run with two cylinders (2&3) if 1&4 plugs removed (even then it requires some throttle or idle adjust).Although It seemed utilize also cylinder #2 during last test drive. So spark isn't all gone..

I have been busy to sell my old Vette (so, now I'm officially just a biker, if we speak about vehicles for hobbies..). I'll try to finally get those breaker's contact points from the shop and will report again. Thanks.

[BadBillyB]

Sounds to me like your carbs are out of synch......BadBillyB