Uhhhggg!! Sometimes I hate carburators.

[JTGS850GL]

Just finished doing a complete strip and dip and sonic cleaning of my new to me set of GS1100G carbs. Everything mounted up, snugged up and ready to run. Start her up and everything seems fine except for one thing... Exhaust #4 not getting hot.

Seems to rev up nice but no fire on #4 at idle or even a little above. I checked for spark and compression and all is perfect. Cylinders 4 and 3 match at about 160psi warm and #4 has a nice bright blue spark. New plug caps as well. Plug seems to have liquid gas on it and no carbon buildup. Adding choke doesn't bring it back either. I can take the air filter off and put my hand over the carb. I feel strong vacuum but no change in idle. Do the same for any of the other three and the engine tries to die.

All carbs are in sync and valves adjusted. I tapped the float to make sure it's not stuck. Pulled plug wires while running on each cylinder. All create a significant drop in RPMs except for #4. Decided to swap the carb bank with the ones I had set up on the original 1000G engine. Now all 4 have fire again.

Guess it's time to tare things back down on number 4 and see what I missed. Maybe swap the body from one of my cleaned spares first. Really frustrating since everything was cleaned up and checked out great when squiring carb cleaner through all the passages. Vacuum sync shows all 4 cylinders equal.

Thanks for putting up with my rant. Just frustrated with the lost time. Really want to get this bike back on the road since weather is getting much better lately. Also want to get the GS850GL sold so I can start my next project.

[Steve]

At least you have done all the proper troubleshooting and narrowed it down to carb #4.

I was going to suggest cleaning the pilot circuit, but you said that the "choke" didn't help, either. Pull the drain screw, make sure you have gas in the bowl.

How far out did you set the mixture (pilot) screws? I usually start with three full turns, then fine-tune when it warms up. Giving the extra turn richens the mixture, sort of acting a bit like a 'choke', allowing it to start easier. Note that not all the screws will end up at the same setting. I had one carb on my son's bike that took about one full turn more than the others.

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[JTGS850GL]

Originally set all mixture screws to 2 1/2 turns. Once I noticed I had an issue, I screwed the mixture screw on #4 to seat and then backed up out until about 4 turns but the cylinder never came alive. Now I you have me thinking about it... I need to see if there isn't a broken tip in there. Still the choke addition should have brought it back I would think. Really strange. Almost like it's flooding cylinder #4 instead of being lean. I'll go back and check the float level next.

[eddie21]

This is how carburetors work, (in my mind). They drive me nuts too.

[JTGS850GL]

The problem is, even if you know how they work, without X-Ray vision it's impossible to KNOW that you've got all those tiny passages clean. It's even possible that you get the gunk loose and it just ends up moving to somewhere else smaller. Each carb was dipped for 24 hours, then sonic cleaned for 30 minutes, rinsed and then air sprayed through. After that, each passage that I could verify was sprayed through with carb cleaner.

I wish there was a definitive way of verifying that every passage is completely clear and open. These carbs were pretty bad when I first received them so I'm probably lucky that only one is giving me any trouble. Float bowls had so much crap built up in them that one bowl was glued to the main jet. Right now they look like new.

[chuck hahn]

The sync between 3 and 4 is off. loosen the adjuster nut and move the adjuster and she will fire off. May need to add a little on the idle knob as well. Basically all the other butterflies are open enough and carb 4 is too closed.

[jsandidge]

I'm willing to bet Chuck is right on this one. (he usually is). You would think it would still light off with some throttle though, when the butterflies have opened up some.

[chuck hahn]

His initial statement said something about it hitting with a little more throttle..which is exactly as you say. Then when you let off the grip and it returns to the idle stop the cylinder goes dead again. Classic symptom of a off kilter sync.

EDIT TO POST....Just reread it more carefully. He said the plug has gas on it but theres no fire. So I stand corrected. So now, i would consider a bad plug. Yes I have taken them out and held them against the engine and nice hot blue flash. Put it in and dead cylinder..repeat a dozen times and get same results. Throw in a new plug and abra ka dabra!!!

And yes I would recheck that pilot screws tip. 4 out seems like it would be god aweful rich to me. The 2 to 2/12 out is whats touted here as the optimal start point with some minor adjusting there after.

And if the wires are still plenty long cut about 1/4 inch off and rescrew the caps into clean fresh wires.

[JTGS850GL]

I really do appreciate the input Chuck. I'm still leaning on a carb #4 issue because the cylinder fires off with the GS1000 carbs installed. I would think that it should rule out the plug as being the source of the problem since it is firing now. Plug caps are virtually new and everything worked great with the 1000 engine installed. Only reason for swapping in the 1100 engine was a vibration in the 1000 engine prompted me to take it down for some rework. The 1100 engine just happened to be a plus. I'll look at the balance between carbs 3 and 4 but the manometer registered that 1 through 4 were in balance. I'll let you know once I swap out the #4 carb and see what happens.

[chuck hahn]

I missed the part about the 1000 carbs all worked when swapped out..so this adds a new perspective for sure. And your probably spot on lif your using a different set and style of carb. Funny how fickle they can be isnt it. Whats the vibration thing with the other engine all about????

[Nessism]

Did you hold the pilot jets up to the light to make sure they are open. Spray carb cleaner through the choke pickup tube and watch to see it come out into the choke plunger cavity? Check the pilot hole in the carb throat while squirting carb spray through the pilot passage to make sure the fluid sprays out?

[chuck hahn]

Wonder if the pilot jet rubber plug is leaking? That would make the cylinder flood and gas foul a plug in seconds. I am of course assuming these are then CV carbs for the 1100 engine.

[jagdriver]

I worked on the carbs of my son's KZ550 and could not get #3 cylinder to run at idle. We swapped out plugs, plug wires, Checked valve clearance, ran a compression test, checked sync and nothing fixed it. I had the carbs apart 5 times and could find nothing wrong. Until...... The last time I had #3 carb apart and took out the pilot jet, I sprayed carb cleaner through it and noticed it was coming out between the base plate and the carb body. The carbs on this bike were badly corroded just like yours. On the back of the carb one of the steel plugs for the idle circuit had corroded and fallen out. I put it back in the hole drove it home and sealed it with a drop of epoxy. The bike ran like a sewing machine after that. Of course it did, it had just a very complete full tune up!

So inspect the carbs closely paying particular attention the the condition of all of the sealing plugs, even those you can't see behind the main mounting frame.

[JTGS850GL]

I have a complete extra carb body. My plan is to swap all the jets and slides into it and see if that clears the problem. I'm pretty sure that all the jets are clean and open so it must be a carb body related issue. Once I have the system working I'll go back and inspect the original body and see if I can identify the problem. Thanks for all the input guys. Nice to know that others are there sometimes.

[mikerophone]

Along for the ride as I just literally finished two sets of carbs and I have another one in the works now...curious to know how this turns out.