Strange Issue on a 1982 GS850G Rebuild

[wingnut357]

Greetings all. If this is not the right forum, please forgive my inexperience.

I recently picked up a filthy, but apparently mechanically sound GS850 that would barely (and roughly) idle and die upon any throttle application. It's clearly been sitting since the late 90s. It had recently had the tank cleaned and the plugs and oil changed, but that's it.

It also had a massive oil leak from the head gasket between cyls 1-2.

I'm looking to restore it as close to factory as I can, because I love the look of these older bikes.

Work done so far:

• Head pulled, cleaned and all gaskets replaced. Every thing was pretty carboned and oily, but the cams, bores, and pistons look factory new.
• Calipers rebuilt, new master cylinders and lines.
• New battery.
• Carbs rebuilt (although I don't really know what I'm doing here)

Here's the strange thing. Only cylinders 3-4 are firing, but they seem to be running well (I'm shocked that it will rev to 6k on 2 cylinders), while 1-2 are completely dead.

To troubleshoot, I:

• Swapped 1-4 plugs, no change, so probably not the plugs.
• Swapped 1,3 and 2,4 wires, no change, so probably not the coils or ignition. I did notice that the wires will shock the absolute hell out of you if you try to ground a plug on the outside of the block to check the spark, which seems suspicious.
• Tested compression, got around 120 across all 4 cylinders, so probably not the issue.
• Checked the carb float on 1, which was completely full, so there's fuel in there.

I'm thinking that the 1,2 carbs have to be the culprit, but since it's a little more difficult to move them around, I haven't tried swapping them yet.
Is it possible that carbs 1-2 are so out of tune that those cylinders won't fire? Any troubleshooting tips?

I'm not looking forward to pulling the carbs on and off the intake tubes between adjustments.

IMG-20210519-WA0002.jpg

[Markrkolb]

You could spray a little carb cleaner in 1 or 2 to see if it fires- if not you can eliminate fuel and concentrate on ignition. Just an idea….

[steve murdoch]

Welcome to the site, Wingnut.
A full carb rebuild would be the first thing on the agenda.

http://zeus.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

Nice looking bike.

[wingnut357]

Welcome to the site, Wingnut.
A full carb rebuild would be the first thing on the agenda.

http://zeus.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

Nice looking bike.

That's an awesome guide. Thank you very much.

[wingnut357]

You could spray a little carb cleaner in 1 or 2 to see if it fires- if not you can eliminate fuel and concentrate on ignition. Just an idea….

Thank you, I'll try that tonight. If it doesn't work, I'll follow the guide that's been posted.

[Nessism]

Clean carbs per tutorial and replace O-rings. Adjust valves. Review all items in the Newbie Mistakes thread and make sure you are not missing anything.

Shortcuts are long cuts. Doing all maintenance up front pays off in trouble free long term operation. Pay me now or pay me later.

[GregT]

Are the plug leads on the correct cylinders ? the pairings are 1 - 4 and 2 - 3. If you have only one of a pair on the right plug, you'll get the symptoms you have now.

[Rijko]

I did notice that the wires will shock the absolute hell out of you if you try to ground a plug on the outside of the block to check the spark

I just re-read your posting to see if there was anything i missed the 1st time.
And i did, your casual mention of being shocked "the absolute hell out of"

Thanks for the big grin on my face, having been there like many of us i know exactly what you mean !

Just hang in there, the guys on this forum know their stuff and we should be able to tackle this with you.

[Rijko]

Here's the strange thing. Only cylinders 3-4 are firing, but they seem to be running well (I'm shocked that it will rev to 6k on 2 cylinders), while 1-2 are completely dead.

To troubleshoot, I:

• Swapped 1-4 plugs, no change, so probably not the plugs.
• Swapped 1,3 and 2,4 wires, no change, so probably not the coils or ignition.

What do you mean by completely dead - not firing or no spark ?
The coils fire both wires on a coil at the same time, so do you have a spark at 1/4 and 2/3 at the same time ?

Have you replaced the 4 o-rings between carb boot and head ?

[wingnut357]

Update:

It's definitely lack of fuel on carbs 1-2. I bought some starter fluid, pulled the airbox, and sprayed it in the throats of 1 and 2 and it surged nicely.

I cleaned all the carbs, but clearly deeper treatment was needed for 1-2, so I'll follow the posted procedure to completely take them down and see what happens.

Then it's time for cleaning the rest of the bike and some additional pictures.

Thank you for all the replies and especially the carb guide. Hopefully I can return the favor.

[Markrkolb]

You sound like you are a much better mechanic than i am but if carbs are not your thing you can send them off. Chuck Hahn, Steve and others will fix them right if you need help. Chuck has a set of mine now😀