First time carb syncher requesting tips.

[woodsietx]

1981 GS 750E.

I am about to head over to finish putting on my valve cover and installing a new tach gear. I have my rebuilt carbs in hand and want to put them on and possibly synch them up.

Is is possible to synch the carbs with no tach? If possible, is it recommended?

I read it is good to put a thin layer of white lithium grease on the edge of the carb boots to facilitate removal later. Is that safe to do on both sides of the carbs?

I have a V&H 4-1, stock airbox with a K&N filter. I believe that I should set the carbs to the same level in the gauge? I bought a CarbTune and have yet to use it.

Any other pitfalls or surprises I should be aware of? I'll have a laptop with the service manual with me.

Thanks.

Woodsie

[woodsietx]

Follow-up question:

Is there anything special about the plug screws in the carb intakes? If I replace them with stainless will that cause me any trouble?

Woodsie

[BassCliff]

Hi,

Is is possible to synch the carbs with no tach? If possible, is it recommended?

Normally you will set your vacuum levels at around 2000rpm. Use your throttle adjustment screw to raise your idle a little while you sync.

I read it is good to put a thin layer of white lithium grease on the edge of the carb boots to facilitate removal later. Is that safe to do on both sides of the carbs?

A little lube won't hurt and will facilitate the installation.

I have a V&H 4-1, stock airbox with a K&N filter. I believe that I should set the carbs to the same level in the gauge?

I'm assuming that you have all the proper jetting paraphernalia (like a Stage 3 kit). Yes, sync them up straight across, all the same level.


Thank you for your indulgence,

BassCliff

[TheCafeKid]

ACtually, he said he has a 4-1 with the stock airbox and a KN filter..He'd need a stage one kit...

At any rate, ASSUMING you have taken care of your jetting (you HAVE done that right? Sync will do nothing to help that, its simply to balance the effects of vaccum from one carb to the next based on what the cylinder is pulling..) Ive recently been playing with a sync tool and vacuum style carbs myself. Its a bit tricky, unlike the mechanical carbs, which have independent control of sync, the vacuum carbs are effected by eachother...

Carb #3 is the "Master Carb" so you need to balance the REST to it. The best way *I* have learned is to follow THIS proceedure, YMMV:

Set the RPMs around 2-2500RPM
Balance #4 to #3
Balance #2 to #3...notice that it will CHANGE #4, so you may have to go back and play with that one..take note of how MUCH it was messed with by #2, and take that into consideration.
Now do #2 again, and HOPEFULLY it will fall in line with 3 and 4
Then balance #1 to #2...again, it will likely mess with them all...

When doing this, you will NEED to have a couple of box fans blowing DIRECTLY on your bike's head. It may take a little while to get them to sync, and you dont want to cook your head. If its taking TOO long, shut the bike off for a while and let it cool down a bit, then start again. Be patient. THIS IS THE MOST IMPORTANT PART.

Good luck, hope this helps...

[cavehamster]

The Suzuki manual says that (in a round-about sort of way) that 1-2 and 3-4 are ganged together (ie, the set screw between each will adjust them against each other) and that the middle set screw will balance the two sets.

Clear as mud?

I found it easiest to mess with the set screw between 3-4 so they are balanced, then balance 1-2 against each other, and then use the middle screw to pull the 1-2 set into balance with the other guys.

Before you do all this, make sure you have your air bleed screws set as well. Don't be like me, though: make sure your idle is around 1000 RPM when you mess with the air bleed, or else the engine will be going too fast and that circuit will not make any difference, and you'll tear your hair out trying to set them. I set my air bleed screws via the 'ol highest idle trick... rotate until you get the best idle, re-adjust the idle RPM back to around 1000, lather, rinse, repeat, then do a carb sync.

Make sure you have some airflow around the engine. I didn't have a spare fan, so I tried to work quickly and let it cool if I started messing up

Once you think you have it, rev it up to like 5000 or so, and make sure it is all still sync'd. Don't forget to lock down the sync screws and double check the sync when you are done.

Note that the Suzuki shop manual also indicates that the outside cylinders, ie, 1 and 4, will pull a little more vacuum, when using the recommended steel ball gauge. This is due to the air box design. I couldn't duplicate this with my vacuum gauges and a 4-1 exhaust, so I just set them equal.

I didn't put a Stage 1 on mine with the new 4-1 exhaust... maybe I should. Ah well, going for fuel injection this winter.

[Steve]

Carb #3 is the "Master Carb" so you need to balance the REST to it. The best way *I* have learned is to follow THIS proceedure, YMMV:

Set the RPMs around 2-2500RPM
Balance #4 to #3
Balance #2 to #3...notice that it will CHANGE #4, so you may have to go back and play with that one..take note of how MUCH it was messed with by #2, and take that into consideration.
Now do #2 again, and HOPEFULLY it will fall in line with 3 and 4
Then balance #1 to #2...again, it will likely mess with them all...

Actually, Your Mileage Should Vary just a bit.

The Suzuki manual says just about the same thing, but the order is different. Sync #2 to #3, adjust #1 to a level slightly higher, then match #4 to #1. Not sure if it make a whole lot of difference, just be aware that when you adjust #2 to match #3, #1 will follow it as it is slaved off the other side. And, yes, adjusting one WILL affect the others. This is why it is best to have a gauge set that allows you to see all four vacuum levels at the same time.

The Suzuki manual says that (in a round-about sort of way) that 1-2 and 3-4 are ganged together (ie, the set screw between each will adjust them against each other) and that the middle set screw will balance the two sets.

Clear as mud?

I found it easiest to mess with the set screw between 3-4 so they are balanced, then balance 1-2 against each other, and then use the middle screw to pull the 1-2 set into balance with the other guys.

Before you do all this, make sure you have your air bleed screws set as well. Don't be like me, though: make sure your idle is around 1000 RPM when you mess with the air bleed, or else the engine will be going too fast and that circuit will not make any difference, and you'll tear your hair out trying to set them. I set my air bleed screws via the 'ol highest idle trick... rotate until you get the best idle, re-adjust the idle RPM back to around 1000, lather, rinse, repeat, then do a carb sync.

Make sure you have some airflow around the engine. I didn't have a spare fan, so I tried to work quickly and let it cool if I started messing up

Once you think you have it, rev it up to like 5000 or so, and make sure it is all still sync'd. Don't forget to lock down the sync screws and double check the sync when you are done.

Note that the Suzuki shop manual also indicates that the outside cylinders, ie, 1 and 4, will pull a little more vacuum, when using the recommended steel ball gauge. This is due to the air box design. I couldn't duplicate this with my vacuum gauges and a 4-1 exhaust, so I just set them equal.

I didn't put a Stage 1 on mine with the new 4-1 exhaust... maybe I should. Ah well, going for fuel injection this winter.

Several issues going here.

1. Where did you see, even in a "round-about way", that you should balance 1&2, then 3&4, then balance the pairs? As mentioned above, the Suzuki manual says that the order is to make the necessary adjustments between 2&3, then 1&2, then 3&4. There are no "pairs" involved.

2. There are no "air bleed screws" in the BS series (CV) carbs. The only adjustment on the outside of the carbs is the "idle mixture adjustment screw". It actually controls a mixture of fuel and air, so it's not really a 'fuel' screw or an 'air' screw, it's a 'mixture' screw.

The 'circuit' that the screw adjusts will actually be feeding fuel virtually all the time the engine is running, but it's effect is most pronounced at idle and very low thottle openings. At 2000 rpm, with the bike on the centerstand, it will be the only 'circuit' in use. And the determining factor is not so much engine speed as it is throttle opening. If you were to be running at 2000 rpm in fourth gear and open the throttle, the needle and main circuits would be supplying much more fuel than the idle circuit.

3. The difference in vacuum levels is not "due to the airbox design". The vacuum level is a measure to show how far the throttle is open for that cylinder. The airbox is on the other side of the carbs from the vacuum gauge, how is its design going to affect the vacuum readings. A higher vacuum shows that that throttle blade is closed a little farther and that cylinder is not producing as much power. By slightly reducing the power pulses at the outside cylinders at idle, there is a bit less twisting in the crank, smoothing everything out.

Personally, I had never used that concept of different vacuum until I read the Suzuki manual, and had always set the vacuum levels the same with good results. Could they have been better if they were set according to the manual? I don't know.

If you could not duplicate the vacuum levels, you somehow could not adjust your carbs. I does not matter what you have downstream in the way of an exhaust system, you should be able to adjust your carbs to whatever levels you want. Of course, some levels will work better than others, but you should be able to make the adjustments on the carbs.

.

[tlepac]

Confused yet Woodsie?


Terry

[bmac]

syncing carbs

From reading the suzuki service manual I would like to add( RPM should be set @ 1750). Adjust 2 to 3 then 1 to 4. Depending on Carb sync tool 1and 4 would be set 1/2 ball higher than 2 and 3. I have Motion pro merc. tool and set the 2+3 half a bar less than the 1+4 and runs fine. Bmac
Just adding input, not looking to offend anyone.

[2BRacing]

Together with my GS850GX, I obtained a factory Suzuki manual which unfortunately only described the earlier VM carbs, instead of the BS carbs on that model. According to the description for synchronising the VM carbs, the levels were supposed to be the same on all four gauges.

However, after only recently becoming aware of GSR and all the useful info, I at long last obtained access to the proper factory manual for BS carbs (courtesy Mr BassCliff). Imagine my surprise when noting that 1 & 4 were set slightly higher than 2 & 3 !

I have since wondered why there would be a difference? Could it be due to the balance pipe (or "junction box") between 2 & 3 headers on later 850G models with BS carbs (earlier models with VM carbs did not have that design AFAIK).

How much difference would the different settings really make? Maybe the 4 into 1 designs probably need to be set equally?

Would be interesting to hear what the knowledgeable folk here have to say on this! (not meaning to hijack the original thread!)

[rustybronco]

Imagine my surprise when noting that 1 & 4 were set slightly higher than 2 & 3 !

I have since wondered why there would be a difference? Could it be due to the balance pipe (or "junction box") between 2 & 3 headers on later 850G models with BS carbs...

Yes it's because of the pre-muffler (or whatever you would like to call it)

How much difference would the different settings really make?

My opinion?, not very much difference. there are some people here that set them straight across the board.

[cavehamster]

Actually, Your Mileage Should Vary just a bit.

The Suzuki manual says just about the same thing, but the order is different. Sync #2 to #3, adjust #1 to a level slightly higher, then match #4 to #1. Not sure if it make a whole lot of difference, just be aware that when you adjust #2 to match #3, #1 will follow it as it is slaved off the other side. And, yes, adjusting one WILL affect the others. This is why it is best to have a gauge set that allows you to see all four vacuum levels at the same time.



Several issues going here.

1. Where did you see, even in a "round-about way", that you should balance 1&2, then 3&4, then balance the pairs? As mentioned above, the Suzuki manual says that the order is to make the necessary adjustments between 2&3, then 1&2, then 3&4. There are no "pairs" involved.

Ouch. I don't mean to imply that there are pairs of carbs, but it helps to think about it that way, in terms of how the adjustments work. I mean... carb 3 is 'non-adjustable', so we are setting the carbs off it. The screw to the right of 3 adjusts 4 to 3, only. The screw to the left of 3 adjusts the 'pair' 1 and 2 to 3. The screw between 1 and 2 adjusts 1 to 2, yeah? So, reading various places it seemed recommend that you adjust 3-4, then 1-2, and then adjust the virtual pairs together. The Suzuki manual offers something like this as well, that is to say, something non-obvious that a little mental abstraction makes sense of. Sorry if this is not the accepted way of thinking about it, but it helped me, a beginner, get it done quicker.

2. There are no "air bleed screws" in the BS series (CV) carbs. The only adjustment on the outside of the carbs is the "idle mixture adjustment screw". It actually controls a mixture of fuel and air, so it's not really a 'fuel' screw or an 'air' screw, it's a 'mixture' screw.

The 'circuit' that the screw adjusts will actually be feeding fuel virtually all the time the engine is running, but it's effect is most pronounced at idle and very low thottle openings. At 2000 rpm, with the bike on the centerstand, it will be the only 'circuit' in use. And the determining factor is not so much engine speed as it is throttle opening. If you were to be running at 2000 rpm in fourth gear and open the throttle, the needle and main circuits would be supplying much more fuel than the idle circuit.

You are right, I meant idle mix screw, I got the terminology wrong.

Perhaps it is feeding all the time, but it didn't do a darn thing for me unless I kept the engine under about 1400RPM. I about tore my hair out trying to figure out what was happening. Again, advice from a beginner who had not considered this first time around.

3. The difference in vacuum levels is not "due to the airbox design". The vacuum level is a measure to show how far the throttle is open for that cylinder. The airbox is on the other side of the carbs from the vacuum gauge, how is its design going to affect the vacuum readings. A higher vacuum shows that that throttle blade is closed a little farther and that cylinder is not producing as much power. By slightly reducing the power pulses at the outside cylinders at idle, there is a bit less twisting in the crank, smoothing everything out.

Personally, I had never used that concept of different vacuum until I read the Suzuki manual, and had always set the vacuum levels the same with good results. Could they have been better if they were set according to the manual? I don't know.

I was just going by what I read here: http://bwringer.com/gs/carbsync.html

I assumed that the combination of airbox and exhaust leads to the outer two pulling more, but hey, what do I know?

If you could not duplicate the vacuum levels, you somehow could not adjust your carbs. I does not matter what you have downstream in the way of an exhaust system, you should be able to adjust your carbs to whatever levels you want. Of course, some levels will work better than others, but you should be able to make the adjustments on the carbs.

.

Anyway, sorry if I confused anyone.

[TheCafeKid]

You may also choose to follow the manual proceedure as Steve has said, but MY ABOVE proceedure was taught to me by ANOTHER GSR member, and it takes him about 5 minutes, vs the 20 minutes it took me doing it the books way. Dunno why...just seems to work faster..

[duaneage]

Have a fan or two in front of the bike or it will overheat quickly. Especially when running high RPMs.

I oil the adjusting screws and make sure they are loose before I begin. The #2 carb is tough to get to on CV carbs, I remove the choke lever to gain access. Have several 8 mm open end or 5/16" open end wrenches that can fit in there.

It may be obvious but make sure the valves are adjusted, the plugs are gapped and clean, and everything else is as you want it. Adjusting valves affects the sync greatly since it changes the amount of intake and exhaust flow when you tweak the valves. I've checked sync before and after a valve adjustment and saw a big change.

Check the sync one last time after tightnening the lock screws. A small nudge can throw it all off. You will be rewarded with throttle response that rivals fuel injection when you are done.

[TheCafeKid]

Agreed. And, I never thought i would say this, but actually HAVING that sync tool now (the screwdriver with the little 8mm lock nut wrench on the outside of it) its worth its weight in GOLD! makes the job MUCH easier.

[woodsietx]

Confused yet Woodsie?


Terry

What I find amazing about this question is that I can honestly say I'm not confused. Thanks to 2 months of reading posts.

My carbs were rebuilt by Griffin and all the levels and settings were correct when he took it apart. He found a Stage 1 kit already installed and told me that if I had gone with a local mechanic, they probably would have tossed it all. He took the time to check with Dyna Jet's web site to be sure of the settings.

I still owe him a public thank you which I will do soon.

I spoke to him yesterday about the process again and he concurs about setting the same level since I have a 4-1. He also said that the missing connection in #2-3 exhaust is why.

I am thinking I won't need to adjust the idle screws after his rebuild but I am not sure. That is one thing I'm not entirely clear on the theory of.

All I need to get before I try it is a proper choke cable. By the time I get one, I should have my gauges back.

Did anyone have thoughts about my bolt question? Can I swap out the vacuum plugs for stainless? I did figure out it is easier to loosen the four plugs without the carbs on so I did so.

As for the how-to, I'll review this thread. I like faster and easier but those terms seldom come up when I have automotive tools in my hand.

Thanks for the advice.

Woodsie