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Carb sync for dummies

  • Thread starter Thread starter claygs750e
  • Start date Start date
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claygs750e

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Ok, so I have the carbtune, bought the adapters from Z1 and have everything connected with a golf tee in the vacuum line. Several carb bodies were replaced during this build because the float mounts were broken. Plus the carbs were thoroughly cleaned and rebuilt by the guys from cycle recycle so I trust everything is within spec.

So when I started the sync I warmed up the bike then looked at the tool and the tool was barely registering on any level. I tightened them all down to the same levels and adjusted open from there. The problem I'm having is I can barely see any of the metal bars raise to actually start the sync. The idle is pretty high already, but if I don't keep constant throttle it will die. What am I doing wrong?
 
Yea, I have it connected exactly. Is there a starting point as far as the idle screw and the adjustment screws? Then I can start backing out from there?
 
You should do a good bench sync first. Basically adjust each carb to match the #3 carb with the #3 carb opened slightly. You can use the idle screw to set the #3 to be just open enough for a paper clip or thin feeler gauge to just barely slide through. Then adjust the other three carbs to match using the adjustment screws. Once set you should adjust the idle screw to about 3 turns in from just touching the tab. That should get you started.
 
Is there a video similar to the above (very idiot proof and step by step) for the bench sync procedure? Am looking at getting new carbs w/ a Stage 3 kit and want to make sure everything goes on right the first time.
 
Well after some tweaking I am able to see the bars now which are all pretty close to each other. I wish I could say everything seems ok now, but it's not. I've been playing with the idle mix screw and I ws going between 1.5 to 2.5 turns out and I'm really not sure what's going on. Now the idle is really high no matter what I do with the idle screw knob. That's one problem. The next is when I'm doing the syce and bring the idle down, it will randomly on it's own increase the idle up high for no reason. Then the last problem is every time I start it and the longer I play with it it will eventually not start any longer and cranks very slow. Even though the battery is ok. I thought maybe I flooded it, but I removed the spark plug and it's pretty black and dry. So frustrating! Any ideas? I've been messing with the carbs for weeks now with every problem you can think of.
 
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JTGS850GL said:
You should do a good bench sync first. Basically adjust each carb to match the #3 carb with the #3 carb opened slightly. You can use the idle screw to set the #3 to be just open enough for a paper clip or thin feeler gauge to just barely slide through. Then adjust the other three carbs to match using the adjustment screws. Once set you should adjust the idle screw to about 3 turns in from just touching the tab. That should get you started.
Click to expand...


Good advice here. I am assuming you are using a very good fan to keep the bike cool while you are running it??
 
it's not the best fan, but I am taking breaks between to let it cool and I'm not letting it run longer than 10 mins at a time at the max.
 
Idle is high probably because you have the butterflys too open, ie; you've adjusted the synch too high. What is the vacuum measurment showing on the carbtune? that being said make sure your main idle adjuster is not accidentally adjusted in too far, make sure your throttle cable hasn't somehow become snagged on something, etc.. For your other issue of random RPM increases, that sounds like a vacuum leak. Make sure the carbs are seated properly in all the intake boots and airbox boots, that you have no large exhaust leaks, etc... Thirdly, if the longer you run the bike the harder it is to start it could be any number of things. Bike is running VERY lean and you are causing damage to the engine (check all the plugs to make sure none are white like snow), a loose connection somewhere, ie; battery connections, main ground connections, main power connections in harness or starter relay, etc..etc.. And then of course you could have a charging problem, this can be tested simply with a multimeter and the instructions on Bikecliffs site or from posplayr GSR signature.

http://www.thegsresources.com/_forum/showthread.php?t=164993
 
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Ok so I took your recommendation and did the bench sync, but I have a few questions. The first thing I did was turn the idle knob to get carb 3 open less than the width of the paper clip. Then I adjusted each of the other 3 to match. My question is after I did this do I need to back the idle screw all the way back out and then turn it three times like you mentioned? Or do I adjust the idle knob enough where all 4 carbs are slightly open with the width of the paper clip.
What would you recommend setting the mixture screws on each carb to start with? 2 turns out on each? I've attached pictures with the current setup.
 
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Get the engine warmed up & then set the idle to 1200 rpm. FIRST thing, get the mixture screws adjusted CORRECTLY, using the fastest idle method. THEN you sync the carbs with the rpm at 2500. Get back to us after that.
Ray.
 
claygs750e said:
Ok so I took your recommendation and did the bench sync, but I have a few questions. The first thing I did was turn the idle knob to get carb 3 open less than the width of the paper clip. Then I adjusted each of the other 3 to match. My question is after I did this do I need to back the idle screw all the way back out and then turn it three times like you mentioned? Or do I adjust the idle knob enough where all 4 carbs are slightly open with the width of the paper clip.
What would you recommend setting the mixture screws on each carb to start with? 2 turns out on each? I've attached pictures with the current setup.
Click to expand...

Ok, so all the butterfly's open approx. the same. You turn the main idle adjust. knob in a bit, enough so the bike will have some RPM when you start the bike, you can always adjust it down up once the bike starts. The mixture screws can be set at 2 1/2 -3 turns out, this is just a starting point so the bike will start, then you can fine tune from there. Rays method will work fine as well.
 
On the bench you turn the idle adjustment screw out until it just makes contact with the tab. You then adjust it in 3 full turns. That's your starting position. Once the engine starts and warms up you adjust to the correct idle RPM of around 1100. You can set the mixture screws to around 2 1/2 turns from seated to begin with. Once you're ready to do the dynamic sync you can turn the idle up to around 2500 and do the sync from there. The RPMs may rise as you get closer to proper sync. You may find that you'll have to keep dropping the RPMs back down as you sync the carbs. This is normal. If you find that you have a hanging idle. RPMs stay high after a blip of the throttle, then you may have an air leak to hunt for.
 
That makes sense. I did make a pretty stupid mistake and one of the tubings landing on the pipes and melted so I cut that section off, and reattached the restrictor. it shouldn't make a difference that the particular tubing is shorter than the rest should it?
 
rapidray said:
Get the engine warmed up & then set the idle to 1200 rpm. FIRST thing, get the mixture screws adjusted CORRECTLY, using the fastest idle method. THEN you sync the carbs with the rpm at 2500. Get back to us after that.
Ray.
Click to expand...
That will work if your bench sync is rather close.

I have found that if one carb is closed considerably more than the other three, adjusting its mixture screw and expecting any change is an exercise in futility.

Personally, I will sync the carbs, then, while the gauges are still attached, do my mixture tweaking while watching the gauges. As the engine speeds up with a better mixture (and you don't change the throttle opening), the vacuum levels will rise in ALL cylinders, making adjustment an easy, visual thing, not just listening for subtle changes in idle speed.



JTGS850GL said:
On the bench you turn the idle adjustment screw out until it just makes contact with the tab. You then adjust it in 3 full turns. That's your starting position.
Click to expand...
I am going to try this on the next set of carbs I do for myself, which will be in the next couple of weeks.
It might help me set them somewhat close when I rebuild a set of carbs for somebody else. :D


JTGS850GL said:
Once you're ready to do the dynamic sync you can turn the idle up to around 2500 and do the sync from there.
Click to expand...
Why so high? :-k

The purpose of the sync process is to get them all the same at idle and very low openings. The Suzuki manual calls for 1500-2000, but I have always done it in the 1100-1200 range before I saw the official recommended speed. (I still do mine at 1100-1200.)



claygs750e said:
it shouldn't make a difference that the particular tubing is shorter than the rest should it?
Click to expand...
It will make no difference at all.

.
 
claygs750e said:
That makes sense. I did make a pretty stupid mistake and one of the tubings landing on the pipes and melted so I cut that section off, and reattached the restrictor. it shouldn't make a difference that the particular tubing is shorter than the rest should it?
Click to expand...
I did the same thing when hanging the Carbtune off the handlebar. It makes no difference whatsoever.
 
Steve: I actually do the same as you and sync the carbs at idle. Maybe just a little above like 1500. 1500 turned into 2500 with a little slip of the finger.:eek: Sorry for the confusion.
 
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Ok, so I did the bench sync and they look really close, took the mixture screws all the way out 2.5 turns, and the idle screw 3 turns in after touching the tab. I fired it up and the sync took was almost dead on so I got really excited. Then, as all my recent happy moments was short lived. The idle started going lower and lower and then died. I started it back up and when I pull back the throttle it immediately wants to die. Does it mean I need to tweak the mix screws lower? I tried to turn up the idle knob, but with no effect. I pulled one of the plugs to see if it looks real wet and it looks fine. I feel like I'm real close.
 
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Can you clarify what you mean by "pull back the throttle"? Do you have the choke engaged at this point?
 
Sorry, I mean give it throttle. The choke is not engaged at that point since it ran good for about 3-5 mins. Now it seems like when I give it some gas it bogs down and dies. It was running stead with the choke not engaged and then the idle got lower and lower and then died. Once it seemed like it was going to die I started increasing the idle knob with no help. I do have a golf tee inside the vacuum line attached to the carb. That's ok right?
 
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