Still a Mystery - #3 & #4 not Contributing at Idle

[WingMan71]

All,

I'm still fighting a mystery on my '83 GS650GL restoration project.

Here's where I am now:

1. Valves checked - all in spec.
2. Ignition system checked - I've got spark at all 4 cylinders. (Coil resistance readings are in spec. I swapped the plug wires around twice just to make sure that the symptom stayed with the cylinder and not the plug wire.)
3. Compression good on all 4 cylinders.
4. Carbs rebuilt. (Removed, disassembled, dipped, cleaned and reassembled with all new o-rings per instructions on BikeCliff's web site. Pilot screws are set to 2 full turns out. I've got 20 hours alone in the carb rebuild. I've been very slow and careful with it.

Remaining problem:

#3 and #4 cylinders are still not contributing (running) at idle. If I pull the plug wires off of either #3 or #4 at idle, there is NO change in RPMs at all at idle. If I pull the plug wires off of #1 or #2, the engine dies immediately. So #3 and #4 are definitely not running at idle. As soon as I get off of idle I can tell that #3 and #43 kick in. The bike pulls really hard when you get on it out on the road. There's just no way that it's only running on 2 cylinders when the revs are up. So, I'm convinced that I'm running on all 4 when the carbs are on the Main System. Also, all 4 cylinders are running when the choke is pulled on as well. I can actually feel and hear the difference between idle with choke on and off.

My diagnosis at this point is that I must have a plugged Slow System in the Pilot Circuit somewhere. The question is where?

I followed to the letter both sets of carb cleaning instructions on BikeCliff's site. This one http://www.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf , and this one http://www.mtsac.edu/~cliff/storage/gs/mc_maint/GS_CV_Carb_Cleaning_Series.pdf . I was particularly fond of the "wire brush bristle in a match stick" tool for cleaning out small passages. Nice trick.

My point is that I followed both of those set of instructions to the letter and I still seem to have an idle problem that must be in the pilot circuit somewhere. I made sure that any and all tiny little passages or bleed holes referenced in those instructions was cleaned and cleared and open before I reassembled the carbs. So, I'm searching for what I could possibly have missed.

Here's a picture of the Slow System from the service manual. I've marked a small bleed passage with a red arrow. I DON'T remember any of the instructions showing a bleed passage there, nor including instructions to make sure that that particular bleed passage was cleaned an open. If there was, I would have done it.

So, my question is: Is there really a bleed passage that goes from just underneath the main jet over to just above the pilot jet as shown in this diagram? Or is this more of a functional diagram rather than an exact replica of how the carb is actually built? If it actually is there, I don't remember seeing it, or being directed to inspect/clean it, or to making any special effort at cleaning it. If it's not where this diagram indicates, just exactly where is this bleed passage?

Maybe I got lucky on #1 and #2 and the carb dip cleaned it out, but didn't get #3 and #4 clean. I just don't know at this point. It's a royal pain in the butt to take the carb bank out of a GS650, there just isn't any room. I hate to do it again if I don't have to.

So, what say the rest of you. Is my diagnosis of a plugged pilot circuit somewhere a reasonable explanation of why the bike runs on all 4 at speed and only on #1 and #2 at idle? If not, what else could it be?

And, is there REALLY a bleed passage exactly where the red arrow shows in the diagram?

I could sure use some help noodling this out before I turn another wrench.

Thanks for any advice.

***

 

[chuck hahn]

Loosen the adjustment nuts on the back and readjust the sync screws as it is running. More times than not its just a matter of the butterflies not opening enough. Once you get all 4 hot...then you do the gauge sync. Even though the bench sync " looked really good" this still can happen. had a guy just a few weeks ago i told to do the same thing and like magic....fire!!!!

 

[jsandidge]

Chuck is probably right if your carbs are indeed as clean as you think. There is a passage where you pointed to in the diagram though. I really thought mine were clean too, but I had the same problem with #1. Another dip did the trick for me.

 

[chuck hahn]

If they are getting hot at more throttle than at an idle that means the carbs are working and the pipes do get hot because now the butterflies are open enough.

Then when you go back to idle they stop working means the butterflies are too shut at the idle position to work..follow me???

 

[WingMan71]

Loosen the adjustment nuts on the back and readjust the sync screws as it is running. More times than not its just a matter of the butterflies not opening enough. Once you get all 4 hot...then you do the gauge sync. Even though the bench sync " looked really good" this still can happen. had a guy just a few weeks ago i told to do the same thing and like magic....fire!!!!

Check,

Thanks for the reply. I hope that does the trick. I have only done a bench sync at this point.

I DO remember having to turn the idle speed adjusting screw WAY down when I first fired up the bike. Maybe the butterfly valves are nearly completely closed as a result and not open enough to get the idle circuit to operate. I hope so! That will be an easy fix.

Can I maybe just crank the idle adjusting screw to open the butterfly valves up all at the same time and try that? Or should I just leave the idle screw where it's at and open up the #3 and #4 butterfly valves a bit using the sync screws?

I do have a carb sync tool and I will definitely sycn the carbs on the bike after I get #3 and #4 running.

 

[WingMan71]

Chuck is probably right if your carbs are indeed as clean as you think. There is a passage where you pointed to in the diagram though. I really thought mine were clean too, but I had the same problem with #1. Another dip did the trick for me.

Well... I sure wish ONE of those sets of instructions would have mentioned that bleed passage! Darn!

 

[WingMan71]

If they are getting hot at more throttle than at an idle that means the carbs are working and the pipes do get hot because now the butterflies are open enough.

Then when you go back to idle they stop working means the butterflies are too shut at the idle position to work..follow me???

Chuck,

Thanks for mentioning that. I forgot to mention it. The exhaust pipes wouldn't really get hot at all at idle. I could lay my fingers on them for like 3 or 4 seconds without getting burned, where I could barely touch the #1 and #2 pipes for a fraction of a second without getting burned.

But, when I rode down the road a ways and came back the #3 and #4 pipes were nice and hot. They WERE running on the main system.

Thanks again. Now I have some work to do.

 

[chuck hahn]

Dont worry about the passage right now. Set the idle at around 1200 as its running right now and feel the two pipes as compared to the 2 known good ones. Both are cooler...right??

Run the RPMs up and they get hotter...right? return to idle and they start to cool down and not seem to be running like the others..right???

Readjust the screws that effect 3 and 4 and then recheck the pipes. idle will most likely go up as a result also. get all 4 acting right and do the gauge syncing.

 

[chuck hahn]

Was typing as you were replying. your carbs are fine..the adjustments at the butterflies is off. exactly the symptoms i was suspecting and typed ut.

 

[WingMan71]

OK... note to myself.

If #3 is not open enough to idle, I'm going to have the crank on the idle adjusting screw a bit to open up #3 since it has no sync screw! DUH!

Then I can adjust the #4 sync screw to get #4 open enough to idle.

Thanks everybody. I'll try this tomorrow on my Labor Day vacation!

***

 

[chuck hahn]

Dont take the carbs off. just use a slave tank and adjust the screws till its working. thats all she needs.

 

[chuck hahn]

Yes...3 is the master carb. Turn up the idle till 3 is like it should be. But get everything set up and ready first. Slave tank set up, loosen all the adjuster nuts, have the screw driver ready, etc etc.

This is because your gonna need to adjust the other carbs to get the idle down again have lots of air flowing across the engine too. Soon as you start youll soon see what I mean by be ready to start adjusting the three screws.

Its a process of a tad of adjustment here..a little there. The refinesse them again. Youll get it, I am confident.

 

[WingMan71]

Thanks Chuck and everyone.

I'll try to get this done tomorrow morning before it gets too hot here in Atlanta.

I have an auxiliary tank, carb sync tool, and everything I need to get it done.

I will have to buy you guys a few beers if this fixes it!

 

[Steve]

I do have a carb sync tool and I will definitely sycn the carbs on the bike after I get #3 and #4 running.

Just to make sure you have your head straight on this, ... synchronizing the carbs will bring #3 and #4 "on-line" and get them running.

Just connect the gauges, do the sync, already.

.

 

[WingMan71]

She's alive ! ! !

She's alive ! ! !

SHE'S ALIVE ! ! ! :triumphant:

ALL FOUR CYLINDERS ARE ALIVE AND SHE'S RUNNING GREAT ! ! ! :biggrin:

First thing this morning I hooked up all of my gear. Auxiliary tank, carb sync gauges, etc., and warmed her up.

I first cranked on the idle speed adjustment screw a bit to get #3 running. Then I sync'd #4 to #3 and things improved quickly. That left both #1 and #2 a bit too far open, so I had to back those two off a bit to get all four sync'd. Here's what I had on the gauges at idle:

The hardest part was getting #2 right. My Motion Pro carb sync tool (in picture) could not be connected to the #2 sync nut/screw. A piece of the 650 frame was in the way directly above that nut/screw, so I could not use it on #2. I eventually got the #2 nut loose using an 8mm socket and a flex-shaft screwdriver thingy. It was not easy to get #2 right, but this should be plenty close enough.

SO, SHE'S ALIVE AND RUNNING GREAT ! ! ! :smile-new:

I was surprised at how hard this little 650 pulls! She's pretty eager to get up and go!

THANKS FOR ALL THE HELP. IF YOU EVER GET TO ATLANTA, PM ME FIRST, I OWE YOU GUYS A BEER! :applouse:

***

 

[chuck hahn]

Barqs or A&W for me please.

 

[WingMan71]

Barqs or A&W for me please.

Ahh! ROOT BEER ! ! !

I'm a fan too! You got it!

 

[Steve]

THANKS FOR ALL THE HELP. IF YOU EVER GET TO ATLANTA, PM ME FIRST, I OWE YOU GUYS A BEER! :applouse:

***

Barqs or A&W for me please.

Same here, thank you very much.

.

 

[chuck hahn]

Well!!! Havent posted for a while, so are we to assume that youre getting some saddle time in now? Whats the status???

 

[WingMan71]

Well!!! Havent posted for a while, so are we to assume that youre getting some saddle time in now? Whats the status???

Chuck,

YES! She's running great! See my post #15 in case you missed it.

I've been working on this restoration during my free time since December of 2013, and I'm finally close to being done with her. Just some aluminum polishing left to do and she'll be ready to go to her new owner.

A friend of mine at work wants to buy it for his daughter as a starter bike. She just took her beginner MSF course and got her license.

Here's a shot of her when I first got her back in December of 2013:

A one owner bike that I bought out of an estate sale. She was ridden from 1983 to 1993 and then parked in a garage never to move again until I bought her. I'm over 100 hours into the restoration work and am glad to be nearing the end.

Thanks again for your help!