Fixing up an '81 GS850 - update

[Nayt G]

I didn't know if it made sense to continue this story in the GS Owners forum since it's evolving into more than an introduction.

So I did something I rarely do, and decided to listen to the advice of those around me and see what would happen if I put everything back to stock. I got rid of all the Dynojet Stage 3 stuff and the cheapo pods and patched up my airbox using the guide from BassCliff. It's running WAY better than is was with the pods and Stage 3. No more hanging idle, it doesn't rev up on its own any more, and it doesn't backfire while idling. It seem to be pretty happy until I get to 3500-4000rpm. It starts to stutter and starts backfiring again at 4k+ rpms. I've tried setting the mixture screws on the carbs anywhere between 1.5 - 3.5 turns out, and it seems to be the happiest around 2.5, but still has the same symptoms. So this is where I'm at:

1981 GS850G

New boots between the engine and carbs becasue they were bad, including new O-rings.
Completely disassembled the carburetors and dipped/cleaned everything and replaced all of the O-rings and gaskets.
I had a broken float post on carb #2 so that has been replaced with a new body.
All factory jets in the carbs.
Adjusted float height.
Sealed up the factory airbox and am using an oiled UNI filter.
I didn't realize this myself but it was pointed out to me that this thing does does not have the factory exhaust. It's a 4 into 2, but it's not the one it is supposed to have.
I did the propane method to try and find intake leaks and can't seem to find anything.

So next up on my list: Check the valve clearances, check the spark plugs, and replace the petcock because my oil smells like fuel. And change the oil because it smells like fuel. Also, if anyone has any tips or tricks on how to get the airbox boots to all slide onto the carburetor easily I'd love to hear it. I struggled for what felt like half an hour to get that thing connected, and I'm still not happy with how it's fitted. Am I missing anything on my "Next up" list? The guides and new owner do's and dont's on this site have been super helpful so far.

 

[Nessism]

My preference is to pull the carbs out of the boots on the head and slide them backwards. Then attach the airbox boots to the carbs and tighten the clamps. Lastly, push both the airbox and the carbs forward together until the carbs are seated into the carb boots on the head, and install the bolts holding the airbox to the frame.

 

[jsandidge]

Yeah, the rest of the maintenance on your list is likely to fix your running issues. That leaky petcock could be leaking down the vacuum line into carb #2, causing it to run rich. The valve check is crucial too. As for fitting the airbox, you'd be surprised what new boots will do.

 

[Nayt G]

Yeah, the rest of the maintenance on your list is likely to fix your running issues. That leaky petcock could be leaking down the vacuum line into carb #2, causing it to run rich. The valve check is crucial too. As for fitting the airbox, you'd be surprised what new boots will do.

New airbox boots were certainly considered, but these seem like they are nice and soft and flexible still. I like Nessism's idea of attaching the box to the carbs first. I don't know if I would have ever though of that myself!

 

[wymple]

My Gs850, an 81, had a terrible time with surging and bucking in crosswinds until I got that airbox sealed really well, and new boots.

 

[bwringer]

Yep, even if the old boots still seem flexible, you'll be shocked at how much larger new ones are (more than one person has panicked thinking they received the wrong parts). They shrink over time. They're 37 years old -- it's time.

 

[Nayt G]

1 month later update:

New petcock installed, valve clearances back to within spec (They were all way too tight), oil changed, and new (properly gapped) spark plugs. And Nessism's recommendation to attach the air box to the carb first was spot on - it's nice and tight now.

So it fires right up. It idles nice - no hanging or erratic idle at all. It revs up pretty smooth until I get up into the 5k-ish+ range. It doesn't struggle to get past 3500-4000 any more, but it does start backfiring (popping) a little bit at higher rpms. And now for the really sad part - I noticed that the 2nd cylinder isn't firing. The exhaust is not getting hot at all. I pulled the plug and it has a great spark. There is fuel in the bowl of that carb, so with the complete cleaning and rebuilding of all 4 carbs, I don't know why it wouldn't be getting fuel into the motor. I guess I'm going to have to get myself a compression tester? Also I don't know if it's my imagination or not (probably not) but it seems to have picked up a slight ringing or rattling sound sometimes from what seems like the engine area. Ugh.

I've learned a ton about carburetors in the last 2 months, I guess it's time to learn about the engine!

 

[jsandidge]

Even doing a thorough cleaning per the tutorial, some carb clogs can be very stubborn. I had to clean mine multiple times before they were right. Yes, I had them on and off several times, and I was sure I had them clean each time. I've read posts by many other members who have had the same experience. Carbs are still your most likely problem. #2 is also the carb with the vacuum port to the petcock. Is that hooked up?

 

[Nayt G]

Yep, the vacuum line is connected. I wouldn't be getting any gas at all without that would I? Hoping to find time this week to pull the carbs again, and I ordered a compression tool.

 

[850 Combat]

There are two air passages from the carb bell mouth. The one that goes to the pilot jet emulsion tube and to the progression holes at the carb butterfly valve can be hard to clean. The diagram in the factory manual shows them. You should be able to squirt carb cleaner in the air jet and have it squirt out at the bottom of the pilot where the plug goes, and out of the other openings. If you have the Adobe version of the factory manual which is or was on Bikecliff's site, it is on page 301 of 454. One bike of mine had a very stubbornly blocked air passage which kept it from running on the one cylinder. In my personal experience, the air passages can be stubborn.

http://gsarchive.bwringer.com/mtsac/~cliff/storage/gs/GS850_Manual_HiRes.pdf

 

[Nayt G]

I opened the carbs up again today to see if I could find anything, and I noticed this weird thing. On the #2 carb - the one that I replaced because of a broken float post - the one that that feeds the cylinder that isn't firing - the opening on the tube that sucks the fuel out of the bowl is TINY compared to the other 3. Is it supposed to be like this? If not, do I drill it out?

 

[Nayt G]

Genius boy here just realized he still had the broken one to look at for reference. Yes, the opening is full size on the original that I replaced.

 

[Steve]

Some carbs have the tiny opening for the enrichment circuit ("choke") at the end of the tube, others have them in the mating passage in the float bowl. I don't think it hurts anything to have them in both places, but there should be at least one restrictor in the circuit.

Will that affect how #2 runs? Only when you have the "choke" engaged. When you have the "choke" knob pushed in, no fuel will be flowing through that tube.

.

 

[2BRacing]

…. - I noticed that the 2nd cylinder isn't firing. The exhaust is not getting hot at all. I pulled the plug and it has a great spark. ….

Try swopping the spark plug from another cylinder with #2 cylinder spark plug, and look if the exhaust of #2 cylinder now gets hot (and if the exhaust of the cylinder where you moved #2 spark plug to, now stays cold).

After nearly pulling out what little hair I have left due to a similar situation (plug sparks when out of cylinder, but exhaust does not get hot, and carbs properly cleaned), I replaced that spark plug with another one, and voila! - exhaust got hot quickly!

A very rich mixture (like raw fuel down the vacuum line from faulty petcock) somehow "kills" the spark plug, causing it to spark when out of the engine, but not fire at all when under compression installed in the engine.

 

[Nayt G]

Well I managed to grab that thing with a little drill bit and pull it out and now that cylinder seems to be working. The exhaust is warming up at the same rate as the other 3, where before it wasn't.

 

[Nayt G]

False hope? I fired it up last night when I was trying to get my turn signals working and that pesky 2nd cylinder wasn't firing again!