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**OldVet66** · 10-05-2011, 10:28 PM

You should put some information about your bike in your signature line from the User CP on the left of the upper blue bar . Make, model, year. Makes it a lot easier to answer your questions. Welcome to the forum. Basscliff will be along soon to overwhelm you with his Mega Welcome with tons of very useful information that you will need to make your bike safe, happy and fun to ride. Vacuum leaks at the O-Rings between the motor and carb boots, or just old stiff cracked boots can cause lean spitting like that. Going through thorough maintenance will take care of a lot of those problems. The information should be coming your way soon.

**Larry D** · 10-06-2011, 07:45 AM

Welcome !!

We need to know what bike you have. Sounds like you didn't get the carbs clean enough, please explain exactly how you did that....--or-- the the idle air mixture screws are not adjusted properly making the idle erratic. You also could have air leaks somewhere in the intake system, it must be airtight.

**viper711** · 10-06-2011, 08:10 AM

Thanks for the welcome! I added the bike to my signature but it hasn't shown up.

To clean the carbs I stripped them down and blasted carb cleaner through everything. They were recently rebuilt so I didn't want to soak them and risk destroying seals. They were really clean to begin with.

Is there more than one idle air screw on these? I see the screw with the plastic thumb screw on it, but that's all. (the teeth are stripped so I need to unbolt the tank and slip a screw driver in there)

I have adjusted the mixture screws on each carb, two turns out and then back them out until the idle reaches peak.

**Larry D** · 10-06-2011, 10:37 AM

Originally posted by viper711 View Post

Thanks for the welcome! I added the bike to my signature but it hasn't shown up.

To clean the carbs I stripped them down and blasted carb cleaner through everything. They were recently rebuilt so I didn't want to soak them and risk destroying seals. They were really clean to begin with.

Is there more than one idle air screw on these? I see the screw with the plastic thumb screw on it, but that's all. (the teeth are stripped so I need to unbolt the tank and slip a screw driver in there)

I have adjusted the mixture screws on each carb, two turns out and then back them out until the idle reaches peak.

So, what carbs does it have ? I think they are BS34SS....CV carbs, which is odd for a '79......anyway.....Post up some pics, if you can.

How do you know they were recently rebuilt ? Did you do it ? Have all the internal o-rings been replaced ? This is what should be done.

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http://www.thegsresources.com/gs_carbrebuild.htm

Carbs can look clean, but, the fact of the matter is the o-rings are rubber and will break down after +-30 years and cause problems.

There are idle/air adjust screws on the top of each carb body that controls the mixture at idle. Having them 2 turns out from lightly seated is a good starting point.

**viper711** · 10-06-2011, 11:36 AM

They are the CV Mikuni carbs. You're right, I was told they were rebuilt recently and they looked super clean but I didn't check all of the o-rings and that wouldn't hurt.

I fiddled with the mixture screws some more, but no amount of turning them out from 2-turns stopped the backfire. (Clockwise leans the mixture and counter-clockwise richens it, right?)

Not sure what idle rpm is set to right now, the tach cable is broken.

**Larry D** · 10-06-2011, 01:00 PM

IMHO, the best approach is to dip and rebuild your carbs, yourself, as per the instructions I listed earlier. Get your orings here.

index

http://www.cycleorings.com/

While you're "in there" verify that the jetting is correct and that the idle/air screw tip has not been broken off in the carb body. These carbs have very, very small internal passages that must be clean, just spraying some carb cleaner will not suffice. Make sure your air system airtight and that your getting good spark.

Also, if you're not familiar with bringing a +-30 year old bike back to roadworthiness, spend as much time here as possible. Read and learn as much as you can, these things don't just jump up and run on their own.

Use the search feature, there is a years and years of great info there.

**BassCliff** · 10-06-2011, 01:37 PM

Greetings and Salutations!!

Hi Mr. viper711,

Properly cleaned carbs, tightly sealed air intake system, and well adjusted valves will go a long way toward a well running Suzuki. See the links below.

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

I just stopped by to welcome you to the forum in my own, special way.

If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", "Top 15 Tips For GS Happiness", the Carb Cleanup Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. This is what NOT to do: Top 10 Newbie Mistakes. Now let me roll out the welcome mat for you...

Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed. I will put you on my prayer list.

Thank you for your indulgence,

BassCliff

**1_v8_merc** · 10-06-2011, 02:58 PM

First, pull your plugs out and look at the color.
Are they totally sooted black, wet black,etc?
(just post up some pictures if you want)

I had the same problems on my 750, turns out I was running WAY too rich.
I opened up the Air screws just a little more, and it finally leaned out my plugs.

But I have VM carbs...whilst you have CV's.

**viper711** · 10-07-2011, 08:15 AM

I haven't checked the plugs yet but I did pull the points cover and checked the timing. It was almost fully retarded, and one of the point was barely gapped. I adjusted the points, and advanced the timing (almost all the way) and it's running great.

Does this make sense to you guys? I suppose the spark was firing so late that the mixture was burning as the intake valves opened.

**chuck hahn** · 10-07-2011, 12:17 PM

They may have been cleaned properly and have all the new orings and such. But what i didnt see anyone mention is were they at least closely bench synced when they went thru the rebuild process!! I wouldnt do squat except pull them and do a really close bench sync and THEN see how they react. Get all 4 butterflies as close to the same as you can and set the mixture screws at 2 to 2 1/4 out. And while the carbs are off be sure to put in new carb intake boot orings. And be sure that when you do the bench sync the big idle adjustment knob IS NOT touching the throttle linkage. Sync , touch the knob to the throttle linkage and then add 2 turns to the knob. It may idle a bit high when started but you then adjust the idler a bit and let the bike warm up..keep a fan blowing on the engine. Once its warmed up youll be better able to tell whats happening. If it seems to have improved, then its time to do the guages and get them vac synced.

**chuck hahn** · 10-07-2011, 12:22 PM

They may be perfect in every aspect but if they are way out of sync then nothings gonna be of any value till theyb are..Youve got 4 cylinders basically fighting each other over fuel and ignition. And you will also need to check the timing once its running decently. All these factors tie together to effect an archestra of events that make it all work..proper sync, proper timing, proper fuel ratios..

EDIT..Airbox...with or without it installed? The airbox provides a natural slight vacuum for the carbs. People "fool" them by putting a T shirt over the front of the carb intakes.. best is to actually have it installed as it would be if riding. This is gonna make every involved system influence the carbsas they were designed to do. Youll get the best feedback from the bike if everything is as its supposed to be.

**TheCafeKid** · 10-07-2011, 02:07 PM

He's only got two cylinders there chuckie

but yeah a bench sync is always a good idea.

I see you say you've got it running better now that you've adjusted the points. One thing you can do, if you've got the duckets, is swap the ignition out for a dyna S electronic system. It eliminates the old points and condenser units, set it and forget it. No more replacing and galling and all that truck...

**chuck hahn** · 10-07-2011, 02:26 PM

2,4,10..its all the same principles.

**viper711** · 10-11-2011, 02:58 PM

I placed an order on cycleorings but I chose VM series for some reason (just saw pre-1980, not the 4-cylinder part). Pretty sure they are the BS series (BS34). Can anyone confirm this? They are identical to this picture from the 400-450cc Suzuki manual. Idle/pilot mixture screw is on the side of the carbs as shown by the arrow in the smaller picture

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