Mysterious dead cylinder

[RyanBiggs]

I've had a '79 GS1000E for about 10 years (wow I'm getting old :-D ). I moved up to Seattle a couple of years ago, and never have I ridden it as much, as slowly (in a bunch of obnoxious traffic), or in as much rain as I have since!

About six months ago I noticed that I had lost a little bit of power on an intermittent basis. Because so much of my riding over the winter had been commuting in traffic, it wasn't always obvious. However, the problem got more pronounced and frequent as time went on. Now I'm at maybe 40% power most of the time, although often the bike runs well for a couple of minutes at the beginning of a ride before it cuts out.

Eventually I pulled the plugs and did a compression check. The compression is fine across the board, but plugs 2&3 were sooty, and #3 was plain wet. #1 and #4 looked fine. Grounding the plug bodies with the ignition connected, I found that #3 was not firing, and #2 was intermittent/weak. Secondary resistance across the coil was high, so I figured that was the problem and sprang for a new one. I also cleaned the plugs and regapped them at that point. The bike ran great for a day, but then I was back to the same problem. I can pull the boots off of plugs 2 and 3 while the engine is running, and there is no noticeable change at idle.

Next I cleaned the internals of the plug boots. The spark seemed good when I checked at that point. Again, the thing ran great for a day, then went back to the same problem. I then bought brand new boots, but that didn't help. Everything is new in the secondary circuit of #2 and 3 except the plugs themselves, which I guess is my next thing to try.

I'm pretty sure the #3 cylinder is basically not running, as the header barely warms up. The #2 header gets fairly hot, but I can still pull that spark plug boot off at idle with no effect.

Any ideas? I originally thought this was a carburetion or compression problem, but my initial no spark and disconnected boot results on #2 and 3 made ignition seem like the likely culprit. Could a carburetion problem make #3 just not run at all? These carbs are so simple, that seems unlikely to my ignorant self...

Thanks in advance!

[p_s]

Plugs 2 & 3 share the same coil, so they will either both spark or neither. Suggests an electrical problem. I had this happen to me and the connection at the CDI ("ignitor") was just a little loose. Keep in mind that it takes more volts to spark under compression, so looking for a spark with the plug out isn't a definitive test.

(BTW, I'm in Seattle for the summer and I rode my GS550ES here. But more importantly I am away from my '63 Vespa, so my fingernails have become disturbingly clean. I don't like it, so if you want some tinkering help, PM me.)

[onchiman]

Sounds like cylinders 2-3 are running a bit rich and fouled the plugs. I'd get rid of the old spark plugs and start with a fresh set. Most often once a plug is fouled it's not going to be really cleanable because carbon will re-deposit more quickly and it'll just foul again shortly. Then you can tackle the rich mixture in cyls 2-3 issue.

[doctorgonzo]

Could still be ignition on 2 and 3. Didn't see a wire change in what you'd done, and as stated, could be igniter.

[doctorgonzo]

One more crazy out of left field on carb possibilities. My number 4 was always the one that died. When I had low voltage at coils, always 4 that went dead. When plugs started to foul back when I was running rich, always 4 that croaked first, etc... When I finally got a chance to sync my carbs which one was the one pulling crazy low vacuum compared to the others... #4.

[RyanBiggs]

Thanks for the ideas. I have a Dyna ignition, so I've figured that's probably not the problem since the plugs did spark during the plugs-out cranking test after I replaced the coil. The coil comes with the plug wires, so those got replaced at the same time. Could be resistance in the ignitor connection to the coils though, I suppose. I was suspecting that maybe I have spark during the no-compression check but not under load, as p_s suggests. Sounds like the next step is new plugs and cleaning up the low voltage (ignitor) terminals.

If the thing runs good for a week after that and then quits again, maybe it's running so rich it fouls. I was thinking the #2 and 3 sooty plugs might just be a result of poor spark; we'll see. I replaced the plugs last summer and synced the carbs; the old plugs looked OK then. I'll probably just rebuild the carbs anyway for good measure soon, but right now I'm working at the university, and parking sucks so much that the bike saves me 30 minutes a day or more in commute time. So I've been reluctant to tear into it just yet. That and I'm about to move, bad timing.

p_s, where did you ride up from?

[onchiman]

You mentioned riding slowly in traffic which (depending on your style) may mean your running it at lower speeds and lower throttle openings (more so than previously). So if you find yourself idling a lot and operating mostly at 1/8th throttle most of the time, it means using the pilot circuit a lot. It could be a simple mixture screw adjustment on 2 and 3 is too rich, thus fouling the plugs.

[RyanBiggs]

Quite possible onchiman, thanks for the idea. If new plugs get me going but only temporarily, that's quite likely. Previous to using the bike for the Seattle city commute, I typically didn't spend much time below 50-60 mph and reached full throttle on a regular occasion. These days I (sniff) use the pilot circuit most of the time. Somehow I always have figured that couldn't be good for an old literbike!

For good or ill, the about-to-be-moving is to Wichita, Kansas. This poses some disadvantages to Seattle, but time spent idling in traffic is not one of them. Looking forward to that, and full throttle opportunites once more!

[p_s]

p_s, where did you ride up from?

Champaign, Illinois. Hope you get to enjoy some of the local twisties before your move.

[Scotts]

Hey I live in Wichita. Are you in the Plane business?

Do you have a place picked out yet? I am over on the west side of town.

Scott

[RyanBiggs]

Ah, nice ride p_s! Yeah, gotta get out for a few more rides - Western Washington is so clogged up with traffic (at least when I'm not working/sleeping) that the twisties aren't as inviting as they should be, but I-90/Eastern Washington/Olympic pennisula can be good. Perhaps you've tracked down some good spots I'm not aware of. Maybe we can get a ride in sometime before I leave!

Scotts - yep, going to work for Cessna. Coming into town from the 10th-12th to look for a place. Probably will be towards the east side since I'm working near McConnell, but then again commuting across town isn't exactly the horror it is here in Seattle. Any suggestions?

Won't have a chance to pick up new plugs today, but I think I'll clean them up some tonight and add some idle air to 2 and 3 to see what happens. Does sort of make sense that they might be fouling from a rich idle and not firing well. Same thing happened with some junky old Cessnas I used to fly, if you didn't lean the hell out of them at idle.

[chef1366]

Are you getting at least 12 volts to that coil?

[bwringer]

Also, when's the last time you checked the valve clearances?

Prolly not your main problem, but whenever a power loss type of problem sneaks up slowly like this, it's worth asking.

[RyanBiggs]

Hmm... didn't know you could check the voltage at the primary easily - trying to think about how points work. Been a long time since I've messed with any. So I guess with those, you'd turn the engine until the contact closed, then measure the voltage at the primary leads to the coil? But will that trick still work with the electronic Dyna ignition?

Adjusted the valves about 9 months and maybe 2000 miles ago (mostly I've had short rides this last year). Maybe it could use another - trying to remember if the service interval on that is 1500 or 3000 miles, but it's not like it's never been done. I would think the compresson test would have told me if I had done anything really stupid like adjusted a valve so tight that it didn't close properly.

Thanks for all the help, you guys are awesome.

[Scotts]

I have been here 98. I have only lived on the west side. Goddard and the west side of town. I like it. Kellogg is flat a mess all the time. Derby is close to there might look down there. It seems to be a nice place, from what I have heard.

I will be leaving town when you come in.

Safe travels.

Scott