Carb sinc question
11-10-2011 | 09:58 PM
#1
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Carb sinc question
So I just spent an hour reading old carb sync threads, but I can find what to do as the actual sync process. All the threads talk about the cheap tool build and hose attachments but what then?
I assume you are just trying to balance the liquid levels in the tubes? Do you reset the fuel screws first?
Anyway can someone show me a link, cant find it on Gregs stuff either.
Thanks guys, Joe
I assume you are just trying to balance the liquid levels in the tubes? Do you reset the fuel screws first?
Anyway can someone show me a link, cant find it on Gregs stuff either.
Thanks guys, Joe
11-10-2011 | 10:18 PM
#2
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Don't quote me on this first part, but I believe you set the fuel screws and then sync.
As far as syncing, you are hooking the two lines of your tool up to a vacuum signal on each head and balancing the fluid levels (like you said). That's the basic principal.
So here goes:
The rear head already has a vacuum line coming from it. This is the the small line that runs to your petcock, and is commonly known as the infamous PVLIR line. To splice into this line, you need a "t" joint. Two of the ends of this joint are just run in line with your petcock vacuum line. The third is capped off, used only for syncing the carbs.
The manual has a more complicated way of getting your hose hooked up to the front vacuum signal, which I never understood, but didn't need to b/c of the info I picked up on this site. Stock, your bike has a bolt that pretty much caps the front vacuum signal, seen under your front carb on the right side of your cylinder head:
Here's the easiest thing to do. Buy a "boost joint", which happens to be same piece that is already on your rear cylinder. OEM part number 16214-MB0-000. Now you have a nipple that you can easily attach a vacuum line to. This needs to be capped while you're not using it. The way I do this is with a rubber hose that has a screw in the end of it. Now you have access to the vacuum signal of the front carb easily without doing all the weird connection stuff in the manual.
Ok, so you have the "t" joint in your petcock vacuum line, and the front boost joint. Hook up one vacuum line to each and turn the little sync screw on the left side of your carbs until the fluid is balanced. Then cap off both front and rear cylinder signals, and you can easily re-sync anytime. Did that answer your question?
As far as syncing, you are hooking the two lines of your tool up to a vacuum signal on each head and balancing the fluid levels (like you said). That's the basic principal.
So here goes:
The rear head already has a vacuum line coming from it. This is the the small line that runs to your petcock, and is commonly known as the infamous PVLIR line. To splice into this line, you need a "t" joint. Two of the ends of this joint are just run in line with your petcock vacuum line. The third is capped off, used only for syncing the carbs.
The manual has a more complicated way of getting your hose hooked up to the front vacuum signal, which I never understood, but didn't need to b/c of the info I picked up on this site. Stock, your bike has a bolt that pretty much caps the front vacuum signal, seen under your front carb on the right side of your cylinder head:
Here's the easiest thing to do. Buy a "boost joint", which happens to be same piece that is already on your rear cylinder. OEM part number 16214-MB0-000. Now you have a nipple that you can easily attach a vacuum line to. This needs to be capped while you're not using it. The way I do this is with a rubber hose that has a screw in the end of it. Now you have access to the vacuum signal of the front carb easily without doing all the weird connection stuff in the manual.
Ok, so you have the "t" joint in your petcock vacuum line, and the front boost joint. Hook up one vacuum line to each and turn the little sync screw on the left side of your carbs until the fluid is balanced. Then cap off both front and rear cylinder signals, and you can easily re-sync anytime. Did that answer your question?
11-10-2011 | 10:48 PM
#3
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So I just spent an hour reading old carb sync threads, but I can find what to do as the actual sync process. All the threads talk about the cheap tool build and hose attachments but what then?
I assume you are just trying to balance the liquid levels in the tubes? Do you reset the fuel screws first?
Anyway can someone show me a link, cant find it on Gregs stuff either.
Thanks guys, Joe
I assume you are just trying to balance the liquid levels in the tubes? Do you reset the fuel screws first?
Anyway can someone show me a link, cant find it on Gregs stuff either.
Thanks guys, Joe
)The "liquid in the tubes" is the equivalent of how much each throttle butterfly is open. As we have 2 independent carbs and two independent throttle butterflies (running off of one throttle cable) connected by a linkage. we need to insure that both of them are opening up at the same time by insuring that linkage is set up perfectly for the carbs. When there is even a minute difference in the two butterflies and how open they are, the bike will be "attempting" to accelerate with one cylinder only and hence, why it plays such a role in stuttering in low rpms and backfiring ect.ect... because it is one of the most important times that syncing matters, it also plays a very important role in deceleration when you use engine braking.
Even at fully closed throttle, there is still a marginal amount of air and fuel being pulled into the engine through your idle circuit and A/F screws (take a look at the jetting RPM range chart, link anyone?) to keep the bike at a steady idle/decel.
The vacuum that you are reading on each gauge/level is the amount of back pressure that the throttle butterfly is creating against vacuum (aka the engine). The attempt here is to get the vacuum readings the same because that means that your throttle butterflies are 100% equal and will open 100% the same. Getting it 100% is very challenging as when you start to adjust, you apply light pressure to the screw and as soon as you remove your tool you've just changed your sync ever so slightly.
But that is kind of moot unless you're planning on building a vacuum cabinet with dual feeds and doing your carbs on a bench (one of the perks of rebuilding old kehin carbs
) but this doesn't help much on the large because every engine has different vacuum profiles pending on running conditions (rings, valves, comp... ect). In the manual there is a "service" spec for difference between the two (IIRC) vacuum readings. Anywhere outside of that and you'll see it sputter more frequently but just so long as it's not absurdly different, you shouldn't have all that many problems.
If you want a graphic demonstration of this, next time you have your carbs off, look at the throttle butterflies (intake side of the engine) and adjust the sync screw all the way in or out and you'll see how much the butterflies open.
Now if you want to go through Honda for your little gadgets by all means, but your local plumbing supply store also has an infinite amount of solutions as well. I don't like plastic fittings so I found a small brass "t" that did the exact same thing (I replaced my rear with this too because I had one crack on an older bike and it gave me about 20 hours worth of tracking down the POS).
If your vacuum lines are damaged at all (at the end or anywhere on the line) replace them or remedy the end by snipping the cracked or stretched part and always make sure to use clips on the end of them.
Last edited by bass4dude; 11-10-2011 at 10:50 PM.
11-10-2011 | 10:50 PM
#4
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Wait so the sync is not using the fuel screws at all, just the arrowed allen screw? Nice. I have 2 hawk so I can just transfer on vacuum boost joint from the other bike for the sync process. Thanks.
11-10-2011 | 11:47 PM
#5
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The preset up is to get the fuel screw set and idle set.. THEN sycn them.. That Allen head cap screw in the picture is one of two ports where you attach the Sync set up to . The sync adjustment is done on the carb link, left side of the bike up under the tank...
Picture linked from one of our very own's web site
http://www.superhawk996.net/
Last edited by E.Marquez; 11-10-2011 at 11:59 PM.
11-11-2011 | 12:28 AM
#6
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BTW, the spec in the service manual is the starting point... You can get it sync'ed much, much closer than that, and it's a very good idea to do so...
Also bass4dude missed one thing... The carbs are not opening the butterflies exactly at the same time at idle/high idle, but it should be the same amount... This means the liquid will dance around some, but as long as it's uniform, and equal, that's fine...
Also bass4dude missed one thing... The carbs are not opening the butterflies exactly at the same time at idle/high idle, but it should be the same amount... This means the liquid will dance around some, but as long as it's uniform, and equal, that's fine...
11-11-2011 | 09:00 AM
#7
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The boost joint is like $3. IMO it would be easier just to buy two, that way you don't have to try to get a little allen wrench in there every time you want to sync. I sync pretty often, so maybe this is why I'd recommend it. And just to re-iterate what E-marquez said, the adjustment is the little screw on the side of the carbs. You only really have 3 things to keep track of: Attach one carb sync hose to the front boost joint. Attach the second carb sync hose to the "t" joint in your petcock vacuum line. Adjust the little screw. I find a 7mm socket wrench with an extension works well for this.
11-11-2011 | 09:05 AM
#8
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Ok so still can anyone post the link to the whole procedure? I went to Gregs website & carb sync doesnt seem to be there either. I cant see from that pic (Marquez) what screw we are talking about.
11-11-2011 | 10:20 AM
#9
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heres a link to the "how to" I posted on the UK forum
www.vtr1000.org • View topic - How to balance your carbs
I hope that works, also at the end of the thread one of the lads made a pdf on the subject
www.vtr1000.org • View topic - How to balance your carbs
I hope that works, also at the end of the thread one of the lads made a pdf on the subject
11-11-2011 | 10:26 AM
#10
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Thats a pretty good link.
I did the same thing. Once you have installed the vacum lines ( I zip tie mine to the choke pull to keep them from flapping around) Its a five minute job to balance your carbs. No need to remove the tank to access the adjuster, just use a socket on a small wobble joint. Once you do it, you will see how easy it really is.
I did the same thing. Once you have installed the vacum lines ( I zip tie mine to the choke pull to keep them from flapping around) Its a five minute job to balance your carbs. No need to remove the tank to access the adjuster, just use a socket on a small wobble joint. Once you do it, you will see how easy it really is.
11-11-2011 | 11:39 AM
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couple little tricks found out to be handy is to make sure the vac lines are equal length. Also make sure to plug the line to the tank.(depends on how your routing your lines)
However you route it just make sure lengths are equal and your only getting vac from each cylinder only. Kinda obvious but making a note to you.
Lastly I found it a lot easier to fill the sych tube with as much oil as you can and still have it measure on the yard stick. The more oil the easier it is to adjust. Remember no oil bubbles too. I probably have a total length of 14ft of clear tubing for my homemade synch, and about 5ft is filled with 2 stroke oil. By the way I would use 2stroke oil instead of ATF for sure. If your way off initially then the oil can get sucked into your engine pretty fast. I would rather have 2 stroke oil rather than ATF in my engine! Definitely do not use water as earlier mentioned! That can do real harm to your bike! Duh. The synch on my bike at least is rather touchy. Just a few turns can throw things out of wack pretty fast. Then you can get lost from center pretty quickly. Its hard enough to get at the stinking synch adjuster let alone remembering which way to turn to get balanced to. The more fluid you use gives you more time to figure out which way to adjust before it has a chance to get into your engine. You would think opposite but the more fluid.... the harder it is to move under vacuum.
However you route it just make sure lengths are equal and your only getting vac from each cylinder only. Kinda obvious but making a note to you.
Lastly I found it a lot easier to fill the sych tube with as much oil as you can and still have it measure on the yard stick. The more oil the easier it is to adjust. Remember no oil bubbles too. I probably have a total length of 14ft of clear tubing for my homemade synch, and about 5ft is filled with 2 stroke oil. By the way I would use 2stroke oil instead of ATF for sure. If your way off initially then the oil can get sucked into your engine pretty fast. I would rather have 2 stroke oil rather than ATF in my engine! Definitely do not use water as earlier mentioned! That can do real harm to your bike! Duh. The synch on my bike at least is rather touchy. Just a few turns can throw things out of wack pretty fast. Then you can get lost from center pretty quickly. Its hard enough to get at the stinking synch adjuster let alone remembering which way to turn to get balanced to. The more fluid you use gives you more time to figure out which way to adjust before it has a chance to get into your engine. You would think opposite but the more fluid.... the harder it is to move under vacuum.
Last edited by jeephawk; 11-11-2011 at 03:18 PM.
11-11-2011 | 04:34 PM
#14
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BTW, the spec in the service manual is the starting point... You can get it sync'ed much, much closer than that, and it's a very good idea to do so...
Also bass4dude missed one thing... The carbs are not opening the butterflies exactly at the same time at idle/high idle, but it should be the same amount... This means the liquid will dance around some, but as long as it's uniform, and equal, that's fine...
Also bass4dude missed one thing... The carbs are not opening the butterflies exactly at the same time at idle/high idle, but it should be the same amount... This means the liquid will dance around some, but as long as it's uniform, and equal, that's fine...
The bouncing is from the vacuum pulses from the engine going through it's stroke cycle and the different respective stroke of each cylinder!
If you think syncing a V-twin is hard. Just try an inline 6 where each butterfly is operated off of the one next to it and effects a total of 3 carbs with each adjustment.
40 minutes down the drain, eh?
11-11-2011 | 06:53 PM
#15
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OK so more confusion. the boost joint is attached to the carb or the cylinder? I cant find it in the ronayers fiche for it. Does ron ayers use the same part # as honda?
Scratch that question, it is only listed on the REAR cylinder fiche. Ordered a couple so thats a step. Thanks for all the help.
Scratch that question, it is only listed on the REAR cylinder fiche. Ordered a couple so thats a step. Thanks for all the help.
Last edited by smokinjoe73; 11-11-2011 at 07:08 PM.
11-11-2011 | 08:31 PM
#16
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Again, note that this is not the way that the manual says to do it, which is why your bike doesn't already have the boost joint there. The manual has a more complicated system using that allen head bolt and adapters and I can't remember what.
11-11-2011 | 10:45 PM
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11-12-2011 | 01:11 AM
#19
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Thank you for rephrasing me
The bouncing is from the vacuum pulses from the engine going through it's stroke cycle and the different respective stroke of each cylinder!
If you think syncing a V-twin is hard. Just try an inline 6 where each butterfly is operated off of the one next to it and effects a total of 3 carbs with each adjustment. 40 minutes down the drain, eh?
The bouncing is from the vacuum pulses from the engine going through it's stroke cycle and the different respective stroke of each cylinder!
If you think syncing a V-twin is hard. Just try an inline 6 where each butterfly is operated off of the one next to it and effects a total of 3 carbs with each adjustment.
40 minutes down the drain, eh?Well... As for rephrasing... It seems if we work together, we can get it right...
11-12-2011 | 01:14 AM
#20
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I agree with E.Marquez... With small hands you can... With my big one's not a chance... I'd say open up and install... Then you can access all of it and do the sync without fiddling at all, so in the end it's a win...
11-12-2011 | 10:40 AM
#21
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After you get a little practice this is a fifteen minute procedure. Hold the tank up with a small ratchet strap between the front tab and the rear subframe near the tail light wiring. Of course the engine is pre-warmed.
If you look closely at the pic above, you can see red where the fish tank tubing attaches to carb hoses. This is the secret to slowing the oil flow, to keep it a a manageable rate so you don't get the oil too far up the lines and into the carbs, and/or get air bubbles into the oil. Before i did this, the oil moved so fast it was difficult to manage to stop it before it got close to the carbs. If you do get the oil too lopsided, you need to let things settle for a while or twirl the board and tubing so that centrifugal force equalizes the oil in the tubing. Once you get the process, you will no longer need to be concerned with this extra bullshit because it won't happen.
These red inserts are wd40/other lube tubes which come on all spray cans. Cut a 1.5" length for each tube and push them into each tube end. I also put a piece of blue tape on one hose so I know to hook it up to the same carb each time. The reason for this is that the bike will run out of fuel when idling after a few minutes. Then you need to disconnect the tubing, hook the carb tubing back up and run the engine for a minute to get more gas back in the carbs.
the thing that helps me is to know which direction you're turning the sync screw in relation to which way the oil is moving in the tubing. So as soon as you start the engine(idle at 1000 or low as it can idle), note the direction of oil flow and turn the screw a hair to see if it stops, slows or changes directions. As soon as the oil moves up the tubing, you need to turn the screw a hair in the opp direction.
Once you get good at it, you can move the oil back to even with the adjuster screw and stop it, then turn the opp direction to stop it. When you do it this way, you will run out of fuel and have to disconnect and reconnect again, and this is when when you need to remember which direction you are turning the screw when re-connect after refueling the carbs.
This is complicated to describe, but easy as pie once you get some practice. The thing to remember is that there is very very very little movement of the adjuster screw to reverse directions and/or to hole the oil from moving up or down. In other words, if your bike is running okay and you just want to check the sync, you know that it's very close and movement of the adjuster screw will be next to nothing.
As an aside, I would never pull the tank for this procedure as it's so simple and quick to strap it up and to be used for your fuel source. It only takes a minute to reconnect to re-fuel the carbs.
11-12-2011 | 12:20 PM
#23
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It took me and Steve last year hours to get it down, mostly because the oil moved so quickly that I was spending a lot of time getting the oil calmed down and finding that there was so little movement in the adjuster to sync. When the oil is moving quickly in one direction(with the baffles in the tubing), you know you need to go in the other direction until it stops moving, and then you can assume you may have to back the adjuster up a hair to be correct. And that's why it helps to tape the tubing as a marker so that you know to hook it up to the same carb each time, and since you know the direction you were going, you can eliminate the variables in terms of the adjusting screw. Once you pay your dues a bit, you get it down to a science and it's a quick process, but until then, it can drive you bonkers.
Wish I was there because it's easier to help than describe.
11-12-2011 | 10:05 PM
#26
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Pull caps from two fittings, attach Motion pro gauge set, balance gage, attach to other cylinder, check and adjust Sync. Took me longer to type that then it does to check Sync, not including motor warm up.
11-12-2011 | 10:44 PM
#28
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This is what I do, .. So for me carb Sync is a 5 min deal.. All needed lines are there, and just capped. No Tank to remove, unbolt, or ratchet straps needed.
Pull caps from two fittings, attach Motion pro gauge set, balance gage, attach to other cylinder, check and adjust Sync. Took me longer to type that then it does to check Sync, not including motor warm up.
Pull caps from two fittings, attach Motion pro gauge set, balance gage, attach to other cylinder, check and adjust Sync. Took me longer to type that then it does to check Sync, not including motor warm up.
11-13-2011 | 08:01 AM
#29
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It definitely felt smoother, idled more steadily, but nothing major in terms performance that i could determine. The thing that amazed me is the tiny amount of movement of the adjuster between in sync and out of sync.
the SH motor is a borderline raucous, noisy, vibrating, spitting, snorting, and backfiring beast and a carb sync will temper some of these symptoms as will a valve and cct adjustment.
11-13-2011 | 04:37 PM
#30
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If you're used to I4s, you won't know what v-twin engine braking is until you do it right.
Outside of that it won't turn it into a "NEW BIKE" unless of course it died at every stop light from being out of sync. Even then, ball park will make a world of difference.
But I advise taking a quick minute to sync every time you take the carbs off.
Mine are bolted pretty securely to the brackets but when I pull them off and put them back in, it changes by enough to make my slightly crazed a$$ notice.
