I wish I were mechanically savvy...

[randyshipp]

Despite the best efforts of me and my dad, I feel like I'm only inching towards having my new 1980 GS850GL on the road for good. The other day I took the wife for a trip on it and thought things were going OK, but some investigation into its sort of rough sound and poor power led to me spit-testing the headers. Sure enough, number 2 (left inboard) cylinder was all but cold. Didn't even evaporate the spit after a 20 mile ride.

So, today I replaced took new plugs out to the driveway. First I started the bike, got it warmed up and idling, and then pulled the number 2 wire. That was my first surprise, since it zapped me pretty good through the boot. That's not normal, is it? The boot isn't cracked or visibly damaged, but it sure seemed like the wire was leaking, cause it was a pretty good shock.

I shut the bike off, pulled the #2 plug, stuck it in the boot, and started her up. When I maneuvered the plug into contact with the head, there was what my untrained eye thought was a pretty weak looking spark across the electrode. Not bright or white, but kind of sparky and orangish. (Those are technical terms.) Went ahead and replaced all four plugs, reseated the wires. The plugs that came out were (in order from left to right) medium-brown w/ slight sootiness, black and wet (the cylinder that wasn't firing), black and rather sooty, and tan and healthy looking (again, to my untrained eye).

Then I started it up. Immediately, I could hear and feel a difference. All four cylinders were running, and the #2 header quickly came up to temp, seeming only a little cooler (based on evaporation time of spit) than the others. Encouraged, I threw on my helmet and hit the road. On the side streets, I was very happy -- it felt like a whole new bike! Amazing how not running around on three cylinders improves the experience!

But, when I got out on the highway, problems were immediately apparent. Whereas on three cylinders I'd managed to get up to 65-70 mph (~5K rpm) with some effort, that didn't work now. When I got into 5th gear and about 4500 rpm I started feeling the power intermittently dropping off, causing the bike to rapidly lose speed and kind of gently lurch. Trying to open the throttle a bit to push through this little sticking point didn't help, so I pulled off the highway, only able to maintain about 55mph.

Again, it behaved well on the side roads.

So, any clues? Does this sound like something going bad electrically, like wires or coils? Or might it be starved for fuel at higher rpms? And why would it have been able to hit those higher rpms before I got #2 firing.

And why can't this just run well until the riding season is over? ;-)

Randy...

[rkubik]

things to check

Each coil fires 2 spark plugs (I forget which fires which two plugs, but just follow the spark plug wires back to their respective coils to find out). So if a coil is firing one plug well and not the other, it's a problem in the big wire. Could be something as simple as corrosion in the connector.

Individual carbs could also be a bit plugged with varnish etc., so a cleaning might be in order. It's tedious and time consuming but not that hard or expensive and I found the results are worth it for smooth running.

I have the same bike but an '82. Maybe it's running bad to provide you with a project for the winter LOL.

[maparker]

It sure sounds to me like its time to clean those carbs! I know you don't want to here it but I almost guarentee an improvement in performance. I put off doing mine and thought I just had a weak bike that was too small to really pull me (6'4" 200+). I finally took them off, soaked everything that wasn't rubber or plastic in Berryman's ChemDip and it was a whole different bike!

It sounds to me like you have some clogged passages in one of your circuits...I can never keep straight which comes on when, but I suspect a really good cleaning will have you smiling when you ride


parker

[rustybronco]

You can check the spark plug wires for leakage in a dark garage or what have you room? at night when it is running, (watch out for carbon monoxide) also if your petcock is vacuum operated did you check the vacuum line for fuel leakage in the vacuum line yet ? black and sooty #2 plug = too much fuel, this is only a thought...

[LW_Icarus]

Id replace the wires if you can solder, or the coils if you can't, just on general principle, mine are bad enough I dont ride in the rain because the bike acts up. otherwise they are not causing a problem.
New resistor caps at the wire ends may help, and they are cheap, the NGK replacements are like 3.50 each.
ensure that you have good voltage to the coils positive terminal, alot of the GSs have resistance in the system, mine had about 10 volts to the coils before I fixed it.
try the dark garage thing too, just don't gas yourself,if its running poorly it doesnt take much time to fill a small garage with exhaust.
the 850 should move out pretty good, I tend to agree that the carbs probably need looked at, if you havent already, there are alot of little things to go over, but each one done is another off the list, eventually you'll have a great bike to ride (I absolutely love my 850, now that it runs right )

[bwringer]

You have the textbook symptoms of a bad vacuum diaphragm in the petcock. The wet #2 plug is a dead giveaway.

The vacuum line that operates the petcock is attached on the #2 carb. if the diapragm is leaking, it allows gas to enter this vacuum line and get sucked into the engine, causing #2 to run extremely rich and eventually foul.

Replace or rebuild the petcock. You can find a new petcock or rebuild kit here:

http://crc2onlinecatalog.com/

[bwringer]

The bad vacuum diaphragm in the petcock could also cause the starvation problems at higher RPM because it wouldn't open the petcock all the way.

You should also check for excess rust, dirt, little green men, etc. when you drain the tank to replace the petcock.