Synch vs Balanced

[cowb0y]

Can anyone give me a quick run down on the difference between synching carbs and balancing carbs. Which should be done first? I plan to do both myself, so would appreciate any tips. Thanks fellas. You all have made a novice bike mechanic out of me!! :clap:

 

[crapwacker]

As far as I can say, it would be the same. When you have the carbs apart and put them back together, you 'bench sync' them, which gets them close. Once they are on the bike and running, you sync them with a gauge, at this point you balance the airflow through them. Have you been to BassCliff's website? http://members.dslextreme.com/users/bikecliff/

 

[Danjal]

Same thing. Synching carbs means they all run the same. Balance/synch. Different words for the same deal.

 

[cowb0y]

I thought there was a synch to each carb on the rack (bench synch), then you balanced each carb to the cyclinder it services. But this sounds kinda off to me. What am I missing?

 

[hampshirehog]

Synch(ronisation) and balancing are the same thing. You do a bench synch before you put the carbs on the bike and then a 'fine tune' synch when they're on there with the motor running.

 

[TheCafeKid]

Because no two cylinders are exactly the same, even when new from the factory (unless youre dealing with a blueprinted motor, but these are NOT) each cylinder will pull different amounts of vacuum. Because of this, each carb needs to synced (or balanced) with its corosponding cylinder. This assures that the cylinder is pulling exactly what it needs in terms of AFM (air fuel mixture) to get it to fire in just as strong of a pulse, or relatively so, as the cylinder next to it. There are multiple reasons you want to achieve this balance. For starters, a balanced set of carbs will result in smoother running, which means less buzz in the bars, pegs etc. at all RPMs. Also, smoother idle. Unbalanced carbs can cause a cylinder to load up, and have a stronger pulse than the rest of the cylinders, causing buzz but also putting added stress on one side of the crank and bearings, etc. And of course, balanced carbs will help achieve that perfect AFM to garner maximum HP out of the set up you are running. They all work hand in hand.

A bench sync will go along way in getting you close. As a matter of fact, if you get good at it, and pay attention, you can almost get them synced without the use of a manometer. Heck, when I switched my 1100ES to the BS36 carbs from the 34s, i was very patient in making sure I had a good bench sync, and now im not even sure i want to throw the manometer on it and possibly screw it up because its running so nice. Getting a good bench sync will also keep you from going nuts when you DO do a "dynamic" (manometer) sync. The CV carbs have a master carb. One which the butterfly can not be adjusted on. All of the other carbs are synced to it. In our case, I think most BS racks use the #3 carb as the master. Then you sync #4 to #3, then #1 to #3 and #2 to #1. But, each of these adjustments will effect the other. So if you start off way out, you'll find it very frustrating to get them all in line. I much prefer syncing VM style carbs found on the older GSs (pre 1980) as they each have their own adjustment that will have little effect on the others. I am still working on getting my syncing hand on the CV carbs.

What you're adjusting when you move the sync screws is how much the butterfly valve is open or closed at any given throttle position. You arent trying to get the butterflies themselves exactly the same, you're trying to get the cylinder happy with where its carbs butterfly is set. Just like any screw, adjusting it to the left opens the butterfly, to the right closes it.

Bench syncing will be pretty much the same proceedure but you're going to adjust the butterflies so they're all the same. I usually use a paperclip as my gauge, and open the throttle adjustment screw till i can JUST get the clip under the butterfly valve of #3, and then adjust the screws on the other 3 till they are the same way. Works pretty well..

 

[sscott]

Thanks for that explination for me as well.

I was afraid to ask for embarrassment reasons.

But now that I've admitted that much, I'll ask another.

I thought these carbs didn't have butterflies??

 

[cowb0y]

So as I understand this correctly, the bench synch is a fine tune of the carbs and the dynamic synch is a FINER tune. Is that right?

 

[TheCafeKid]

So as I understand this correctly, the bench synch is a fine tune of the carbs and the dynamic synch is a FINER tune. Is that right?

Well, sorta. A bench sync will get the carbs to the point that the bike will start and run relatively well. The dynamic sync is fine tuning.

 

[TheCafeKid]

Thanks for that explination for me as well.

I was afraid to ask for embarrassment reasons.

But now that I've admitted that much, I'll ask another.

I thought these carbs didn't have butterflies??

Yes, they do. The VM carbs found on the early model GSs (pre 1980) do not. All BS carbs have butterfly valve primary, then a vacuum slide as a secondary valve. On your bikes (after 1980) the throttle twist actually controls only the butterfly valves. Then the vacuum created by the motor pulls the slides up.

 

[Calvin Blackmore]

Because no two cylinders are exactly the same, even when new from the factory (unless youre dealing with a blueprinted motor, but these are NOT) each cylinder will pull different amounts of vacuum. Because of this, each carb needs to synced (or balanced) with its corosponding cylinder...

OMG what ****ing horse**** ther is no way a japanese motor would be so offbalance your assertion is ludicrous absolute nonsense

if not give soem evidence

what utter garbage to spout in a public forum
it akin to motor oil and oil filter ****e

 

[Fenixgoon]

OMG what ****ing horse**** ther is no way a japanese motor would be so offbalance your assertion is ludicrous absolute nonsense

if not give soem evidence

what utter garbage to spout in a public forum
it akin to motor oil and oil filter ****e

wtf? is this a troll post or is my sarcasm meter broken?

just like anything else, over time, you will need basic maintenance done. carburetor balancing is apart of that. ESPECIALLY when carbs are rebuilt from cleaning. balancing and syncing are two names for the same thing - equalizing the amount of vacuum drawn by each cylinder.

you can build a DIY kit, but personally I think it'd be better to purchase a carburetor balancing tool rather than making one yourself (motion pro and morgan come to mind).

 

[Calvin Blackmore]

wtf? is this a troll post or is my sarcasm meter broken?

just like anything else, over time, you will need basic maintenance done. carburetor balancing is apart of that. ESPECIALLY when carbs are rebuilt from cleaning. balancing and syncing are two names for the same thing - equalizing the amount of vacuum drawn by each cylinder.

you can build a DIY kit, but personally I think it'd be better to purchase a carburetor balancing tool rather than making one yourself (motion pro and morgan come to mind).

I am speaking of the mass of each piston rod assembly including the mass on each crank lobe

the statistical process control manifest in japanese indusrty would not have allowed a statistically signifigant difference to occur

ballance and blue print is from the days of the model t

 

[Suzuki_Don]

I thought these carbs didn't have butterflies??

Only when they're nervous or anxious.

 

[TheCafeKid]

no its not a troll post but it seems to have attracted one.

I am speaking of the mass of each piston rod assembly including the mass on each crank lobe

the statistical process control manifest in japanese indusrty would not have allowed a statistically signifigant difference to occur

ballance and blue print is from the days of the model t

You obviously know nothing of motor design. There are specific tollerances allowed in mass production. A certain amount of "slop" if you want to call it that. Even a TINY amount of such will cause airflow, vacuum etc differences from cylinder to cylinder.. Piston bores are NOT exactly the same diameter. Which is why when you have a piston kit installed, the pistoned are numbered and matched the bore that was cut for them. The pistons themselves are not the same diameter. Your valve clearances are not the same across the board. The seats are not wearing the same...etc etc etc.

This causes each cylinder to "breathe" differently than another.

I suggest from now on, you check your information before you start spouting yourself.

If these things were all the same, there would be no adjustment, no need for adjustment, and you couldnt adjust them...

Thanks, have a nice day.

 

[Calvin Blackmore]

You obviously know nothing of motor design. There are specific tollerances allowed in mass production. A certain amount of "slop" if you want to call it that. Piston bores are NOT exactly the same diameter. Which is why when you have a piston kit installed, the pistoned are numbered and matched the bore that was cut for them. The pistons themselves are not the same diameter. Your valve clearances are not the same across the board. The seats are not wearing the same...etc etc etc.

This causes each cylinder to "breathe" differently than another.

I suggest from now on, you check your information before you start spouting yourself.

If these things were all the same, there would be no adjustment, no need for adjustment, and you couldnt adjust them...

Thanks, have a nice day.

OH my god a proclamation form mr motor god
I obviously know nothing cause i dare to disagree with you.
newtonian physics is the key here

I need you to tell us all what the difference is cyclinder to cylinder or else quit spewing olf wives tales about balancing


what is the maximum difference you have ever measured god forbid measured cylinder to cylinder

its pure silliness to assume that so many bikes that performedd like perfect meticulus watches off a mass assembly line would be subject to this sort of thing.

numbers please?

 

[Fenixgoon]

OH my god a proclamation form mr motor god
I obviously know nothing cause i dare to disagree with you.
newtonian physics is the key here

I need you to tell us all what the difference is cyclinder to cylinder or else quit spewing olf wives tales about balancing


what is the maximum difference you have ever measured god forbid measured cylinder to cylinder

its pure silliness to assume that so many bikes that performedd like perfect meticulus watches off a mass assembly line would be subject to this sort of thing.

numbers please?

clearly you know nothing about manufacturing. or machining. when you machine things, you specify tolerances - the allowable limits over or under the specified dimensions (for example, I just had some steel machined for me with +- 0.01" tolerances - no length should deviate from my specified drawings by more than 0.01" over or under)

no two products are exactly identical - but they do need to fall within certain manufacturing tolerances about which engineers design in order for things to work properly.

 

[Steve]

The balancing that is being discussed here is NOT the balancing of rotaional or reciprocating masses.

What is being balanced is the amount of air/fuel mixture that each cylinder is allowed to ingest.

When each cylinder is allowed to ingest the same amount as all the others, they are "balanced".
It will affect the smoothness of the engine running because all the power impulses will be the same.

Everybody get your testosterone back in check. :-\\\

.

 

[TheCafeKid]

Break out your verniers and go take measurements yourself bub. They asked for an explaination on why/what a carb balance was/is and why it is needed.
I am not a motor god, never claimed to be. However, I can tell you that this is fact, not fiction, not made up. Hell, take a valve shim. Measure it. Brand new. Marked say 2.70. Is it? Huh? nope. Might be 2.69. Maybe 2.71. Maybe 2.70 on one side and 2.69 on another. Im not saying they're going to have some massive difference in size between one piston to another. Its miniscule. but its there. And that and uneven wear factors across the four cylinders are why carbs need balanced..

Why are you arguing this anyway? Have you never done a carb sync? ever? Ever taken compression readings? Are they the same across your four cylinders??

Im sorry, YOU must be the motor god. Your motors are all perfect, run like swiss watches, and have matching compression all the way across the board. We bow to your superior intellect and mechanical skillz

Troll...

 

[cowb0y]

What if your vacuum lines are off? :-k