Is this a carb issue?

[racerxnico]

Last November I picked up an '84 GS550ES project. It needed all of the normal things a bike that has been neglected needs. After doing all of those things including adjusting valve clearances and giving the carbs a good cleaning.

I got it all back together and it fired right up and ran great. I've been commuting on it since mid-January and now have 1000 miles of shake down running on it.

A few weeks ago it started running rough and acting strange. I pulled the valve cover again to double check the valves. I'd been hearing what sounded like occasional ticking from the top end and just wanted to make sure I hadn't missed anything. Then I balanced the carbs. Truth be told, I hadn't done this when I first put it together because it was running so well. After the balance it was running great again, but it only lasted about a week and a half before it started running poorly again.

Last night, when I got to a friends house, I spritzed the headers and determined that the #3 cylinder wasn't firing. I pulled the plug and it was badly fouled (black). I pulled the other plugs and they all looked a bit lean. I cleaned the plug and tried to adjust the mixture screws a bit (I let my friend confuse me and actually turned them in). It ran fine on the way home and started and ran fine on the way to work.

When I went to leave work, it didn't want to start. After a lot of cranking, I was able to get it to weakly start with no choke. Once it warmed up it ran, but only on three again. I rode it home and pulled the carbs after confirming that the #3 cylinder wasn't firing again. I went through them completely and I couldn't find anything amiss or different about #3. I put them back in, cleaned up the plug again and went for a test drive.

It seemed ok, but not confidence inspiring. If it acts up again are there any clues about what else I should be looking for.

thanks much.

[BassCliff]

Greetings and Salutations!!

Hi Mr. racerxnico,

It could be something as simple as replacing the plug caps. It could be some gunk in the carbs getting stuck in a float valve seat holding the float valve open. Did you properly clean the carbs?

Let me dump a TON if information on you and share some GS lovin'.

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[Graham]

A new plug and a compression check won’t hurt.

[hjfisk]

Are you talking #3 plug as in 3rd from left side as sitting on the bike or 2nd in on left side. the cylinders are 1234 counting from left side in the sitting position. If you are actually looking at it the opposite it could be your petcock leaking by on the vacuum line ,sucking fuel through the vacuum If you are looking at it correctly it could be a stuck fuel float valve.

[spyug]

I immediately think of a bad coil as it seems to act up once the bike gets warm. They can develope breaks in the windings. When the bike is cold the ends touch and when it heats up they seperate breaking down the spark. When the bike cools down again it works properly then as it heats up away it goes again. I'd change the 2/3 coil as it seems to be the one with the issue.

I've had this happen on 2 different bikes in the last 8 years. It is not common but it does happen. Worth looking into.

Good luck.
Spyug

[racerxnico]

First of all, thanks for the responses.

Additional information.

I did properly clean the carbs. I completely stripped them and dipped the jets and emulsion tube. I confirmed that all passages, jets, and airways were clear. I have no reason to believe I missed anything in the carbs as it ran so great for 800 miles.

It can't be the float valve. This bike has the rather unusual arrangement of "single double" carbs. Cylinders 1 & 2 share a float bowl, valve, and vacuum diagphram, same for 3 & 4. If it was the valve, #4 would be rich too. (hjfisk - I am refering to #3 in customary numbering position)

I did order new plugs just in case the one in #3 has some sort of flaw (I may try and swap its position as a test). I'm liking the plug cap theory.

I'd need a little more convincing to think coil. As you say, coil issues usually turn up when it's hot. Yesterday it ran fine on the way into the office, but after sitting for 9 hours, it was difficult to start and then only on 3. If it was a coil issue like you describe wouldn't it start fine and then drop one as it warmed up?

This morning it fired right up, but again only on three. After a idling for a short bit, it picked up and was running on four again. It ran fine for the commute again and I'm praying that it starts for me again at the end of the day.

The plan right now is to replace the plugs and do a compression test. The plug cap and wires look like they're in good shape, but if the new plug doesn't magically fix it, I'll probably try replacing those next.

Thanks again.

[racerxnico]

Grrr,
Problems continue. I have been able to rule out the coils, wires and caps (tried another set, switched two and three, primary problem remains on three).

My compression is great on all four. At this point I think my problem is the igniter. Ran the static resistance tests from the manual on it. Got some weird readings, so now I'm afraid this is the issue. Hoping to find a used part (suzuki wants $600+)

[Big T]

Hmm, I would think that igniter problems would affect 2-3, not just #3.

Especially when the problem didn't move to #2 when you swapped the plug wires

The one black plug is troubling, tho

You've changed the bad plug, or swapped the plugs around?

I've never worked on these weird carbs, where does the vacuum line for the petcock hook up? If it hooks at #3, it's a petcock problem

[Graham]

Shoot some starting fluid in number 3 carb when the bike is running. If the bike tries to run on that cylinder then more then likely it a carb/fuel problem. If not go back to ignition system.

[racerxnico]

One other thing that I did try was to put a hotter plug in the # 3 to see if it would help. It didn't seem to make any difference.

I'm intrigued by the suggestion that it could be a petcock problem. I believe the petcock vacuum line does connect at the #3 side of the right carb. I assumed the petcock works fine as it doesn't leak when lines are disconnected and fuel flows when it is. Are you suggesting that, when vacuum is applied, that I am getting fuel down the vacuum pipe and creating my rich condition?

This is a new avenue to explore. I am going to put a clear line on the petcock and apply vac to see if I'm getting fuel down that line.

thanks

[Big T]

One other thing that I did try was to put a hotter plug in the # 3 to see if it would help. It didn't seem to make any difference.

I'm intrigued by the suggestion that it could be a petcock problem. I believe the petcock vacuum line does connect at the #3 side of the right carb. I assumed the petcock works fine as it doesn't leak when lines are disconnected and fuel flows when it is. Are you suggesting that, when vacuum is applied, that I am getting fuel down the vacuum pipe and creating my rich condition?

This is a new avenue to explore. I am going to put a clear line on the petcock and apply vac to see if I'm getting fuel down that line.

thanks

A hotter plug isn't the answer, as you found

You have correctly diagnosed the situation - gas comes down the vacuum line and richens up the #3, causing it to foul the plug, then #3 fails and the bike runs poorly. The fact that it happened suddenly points the problem to the petcock. The vacuum diaphragm ruptures after 27 years and lets the gas thru.

Does your petcock have a prime position? If it does, cap the vacuum line at the carb and run the bike on Prime and see what happens.

The clear line is a good test also. But, I'd run the bike with it on to test it

[racerxnico]

Praise God. The petcock was the problem. I may still have a problem with my igniter, but the petcock was the issue with #3. I took the tank off, put four new plugs in, blanked off the vacuum line, put an accessory fuel supply in place, and.... it wouldn't run. It started slowly and then died out and wouldn't re-fire. I went inside to eat dinner and pray about what to try next.

When I went back out, I hooked up a vacuum pump to the vacuum spigot on the petock and a drain line to the fuel spigot. I was able to quickly determined that fuel was being drawn into the line, so I decided to try the bike once more. This time it fired right up, warmed, and idled beautifully on all four.

I blanked the vacuum line until I can get a rebuild kit and am going to try to run it like this (switching the petcock between prime to run and on when parked).

Concerned about why it wouldn't start the first time, but maybe I didn't have the fuel flow I thought I did. Or the igniter is going out (I really hope that's not it).

[BassCliff]

Hi,

Did you read your "mega-welcome"?

If so, you probably missed #7 and #13.

Common issues:

1. Intake O-rings (install NEW OEM or Viton only - common nitrile O-rings will quickly deteriorate from heat)
2. Intake Boots (install NEW -- these cannot be repaired)
3. Valve clearances (more important than most people think)
4. Carb/airbox boots
5. Airbox sealing
6. Air filter sealing
7. Petcock (install a NEW one)
8. On '79 models, install new points or Dyna electronic ignition (or at least verify that the old points are working correctly)
9. On all models, it's fairly common to have problems with the spark plug caps. These are $3 or $4 each, and often worth replacing if you're keeping the stock coils/wires.
10. Stock exhaust with NO leaks or holes -- good seals at the head and at the junctions underneath.

What I have noticed at the rallies is that very, very few 850Gs are actually running right. Make VERY sure it's actually running the way it's supposed to before busting out the modifications.

Brian's E-Z and fun plan for GS happiness:

1) Seal the airbox and air filter with weatherstripping.

2) Ensure no intake leaks. Spraying WD-40 or water doesn't tell you much, since very small air leaks can cause problems even though they won't suck in enough WD-40 to make a difference. Replace your intake boot o-rings and boots if needed, and seriously consider spending the lousy $28 for new airbox/carb boots.

3) Ensure clean carbs with correct settings, new o-rings, and original OEM jets. No, not just squirted with something. I mean completely disassembled.

4) Check/adjust valve clearances (Manual calls for every 4,000 miles. This is not optional.)

5) Ensure healthy electrical system.

6) Seriously consider upgrading coils and plug wires.

7) Install new, stock NGK B8-ES plugs gapped to .031".

8 ) Fine-tune float height and idle mixture screw to ensure best off-idle transition.

9) Clean air filter and reinstall with only the lightest oil mist -- over-oiling and/or letting the filter get dirty is a common and critical mistake, and will make the bike run funny at low speeds and run rich. This may take a few tries.

10) Make sure the exhaust seals are sealing.

11) Ooh, much better now, huh? You're gonna need upgraded suspension - Progressive or better fork springs and shocks. Set suspension sag appropriately.

12) Upgrade brakes with new pads and stainless lines to deal with all that extra speed.

13) Install new petcock, since I'm going to head to the roof with a rifle if I have to read about yet another #2 plug fouling and failed hillbilly attempts to rebuild the petcock and/or deny there's a problem.

14) Oh yeah -- check compression somewhere in there to ensure the valves and rings are reasonably healthy.

15) You'll probably need new OEM clutch springs -- the clutches last forever, but the springs get tired after 20 years or so under pressure. E-Z and cheap.

Carburetor maintenance:

Replace the intake boot o-rings, and possibly the intake boots. Here's the procedure:

http://bwringer.com/gs/intakeorings.html

Here's an overview of what happens with this particular problem:

http://cycleorings.com/intake.html

You'll also want to examine the boots between the carbs and the airbox. There's a good chance these are OK, but check them over.
And finally, if things still aren't exactly right, you'll want to order a set of o-rings for BS carbs from the GS owner's best friend, Robert Barr:
http://cycleorings.com
Once you receive these rare rings of delight, then you'll want to thoroughly clean and rebuild your carburetors. Here are step-by-step instructions that make this simple:
http://thegsresources.com/gs_carbrebuild.htm (for CV carbs)
Or for VM carbs: http://www.thegsresources.com/files/vm_carb_rebuild.pdf


Thank you for your indulgence,

BassCliff

[Big T]

Glad to see you have found the problem

Give it a good test this weekend and confirm that turning your petcock from a vacuum to a manual is successful

[racerxnico]

So far so good. Commuted to work and back yesterday and into the office today. In my excitement to be back on two wheels, I forgot to bring my rain pants with me yesterday so, of course, torential rain fall on the way home. In spite of the cold soak, I'm still smiling.