Carb Synch Question

I've been doing this so long with eyes, ears, fingers, etc. that I know using any instrumentation would be a complete failure for me. I'd wind up walking away a befuddled dumbass for sure knowing far less than when I began, and the bike would run like junk or not at all.
 
Eric Bauer said:
Thank you and good question - i'm not sure - I may check with the manufacturer. I'm just wondering that since there is no balance tube in place when checking with the instrument, could the balance tube provide that much difference when connected if there is a significant vacuum difference between the two cylinders. That was my original question, I wasn't really trying to turn this into a how to balance carbs thread. If so I wonder if there is an issue with one of the cylinders. When you rev the engine when connected, the right one certainly shows the biggest change in pressure reading. I am just trying to better understand how this all works
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I'm sure at tickover the balance tube will have some effect even though its a bit small, that's why its there.
When you rev the motor and the right hand pot shows a high vacuum I would suspect the left carb slide is lifting first.
I gave up years ago on balancing instruments for twins and just set everything up mechanically correct. But I do like the look of this sync system.
Dave
 
To jbruney and cash balancing carbs is easy and childs play with carb balance vacuum gauges, if you understand it. I first set the slides up by the drill method just to get them even. The pilot airs crew I use a Gunson's Colourtune, but never in daylight, always in the dark !!! Think about this! It really works, but its total crap in the sunshine.
Then I connect vacuum gauges to each inlet port and balance them at around 1000 rpm until they are equal.
The rh pot moving more than the other on vacum gauge suggests that the throttle cable is pulling unevenly , and needs a minor adjustment . Some carbs are more difficult to tune even than others.
Sorry, but I don't agree with this "balance tube" marlarky, it only confuses the issue, you do not see that on a Jap 4 or 6 for instance, (and I've got them running like a sewing machine, trying that without vacuum gauges) so, if the other bike manufacturers don't fit them you don't need them.
 
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Bernhard said:
To jbruney and cash balancing carbs is easy and childs play with carb balance vacuum gauges, if you understand it. I first set the slides up by the drill method just to get them even. The pilot airs crew I use a Gunson's Colourtune, but never in daylight, always in the dark !!! Think about this! It really works, but its total crap in the sunshine.
Then I connect vacuum gauges to each inlet port and balance them at around 1000 rpm until they are equal.
The rh pot moving more than the other on vacum gauge suggests that the throttle cable is pulling unevenly , and needs a minor adjustment . Some carbs are more difficult to tune even than others.
Sorry, but I don't agree with this "balance tube" marlarky, it only confuses the issue, you do not see that on a Jap 4 or 6 for instance, (and I've got them running like a sewing machine, trying that without vacuum gauges) so, if the other bike manufacturers don't fit them you don't need them.
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This is very helpful - so when you connect and disconnect the vacuum gauges and put the balance tube back on your idle remains the same correct? That's my issue. I set the idle with the vacuum gauges then when I reconnect the balance tube the idle is totally different and way too low. That's my problem and not sure why. I'll look at adjusting throttle cable.
 
I use the Colortune for balancing the carbs at tickover ie on the throttle stops. For throttle open balance I open the throttle handgrip slightly and then let go and listen to the slides hitting the stops, using the adjusters on the carb tops I adjust the cable lengths so the slides hit the stops in sync, then I lock the adjusters. I checked once with a vacuum gauge and this showed they were balanced with the slides off the throttle stops.
 
One thing to be aware of is that syncing at idle does not mean the slides stay in sync as the throttle opens. Reach in and feel the position of the two slides at WOT. They should be clear of the bore by the same amount. You may find that even though they are synched at idle, they are NOT at WOT and therefore NOT at other throttle openings.
 
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Eric Bauer said:
This is very helpful - so when you connect and disconnect the vacuum gauges and put the balance tube back on your idle remains the same correct? That's my issue. I set the idle with the vacuum gauges then when I reconnect the balance tube the idle is totally different and way too low. That's my problem and not sure why. I'll look at adjusting throttle cable.
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Every time you set the throttle with vacuum gauges attached- then you go off on a tangent when you use a balance pipe between two carbs, which feck up your previous settings. Do you not see that? . Forget the balance pipe, block it up with short pipe and a suitable self tapping screw or bolt, and save the hole for vacuum carb access. The engine won't loose any performance whatsoever if yo follow my method. P.S. I assume you did check the ingition timing on both cylinders with a strobe light a degree card ( or marked on the crankshaft) - even a 1degree difference carries some bearing on how the engine performs.
 
Anyone try Gunson carb balancer?
Doesnt use a vacuum port to hook up:

 
Bernhard said:
Every time you set the throttle with vacuum gauges attached- then you go off on a tangent when you use a balance pipe between two carbs, which feck up your previous settings. Do you not see that? . Forget the balance pipe, block it up with short pipe and a suitable self tapping screw or bolt, and save the hole for vacuum carb access. The engine won't loose any performance whatsoever if yo follow my method. P.S. I assume you did check the ingition timing on both cylinders with a strobe light a degree card ( or marked on the crankshaft) - even a 1degree difference carries some bearing on how the engine performs.
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I run into the same problem of the balance tube changing the idle. I block it off by shoving a 1/4" dowel into the balance tube forever.
 
Bernhard said:
Every time you set the throttle with vacuum gauges attached- then you go off on a tangent when you use a balance pipe between two carbs, which feck up your previous settings. Do you not see that? . Forget the balance pipe, block it up with short pipe and a suitable self tapping screw or bolt, and save the hole for vacuum carb access. The engine won't loose any performance whatsoever if yo follow my method. P.S. I assume you did check the ingition timing on both cylinders with a strobe light a degree card ( or marked on the crankshaft) - even a 1degree difference carries some bearing on how the engine performs.
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yes - it has been timed very recently. I did see that issue on the balance pipe which was my question. Sounds like the answer is block it off. Just wasn't sure why it was changing based on the balance tube - I know that's a dumb question. Thank you!
 
Why screw around with gizmos when it can be so easy. Here it is again. Don't knock it until you've tried it.

The easiest way is to putt down the street at about 2000 RPM in 2nd gear (without a helmet) and hold the throttle perfectly steady - then reach back with your foot and cover one ex pipe and then the other with your shoe - listening for the louder pipe. Lower the throttle cable adjustment on the loud side until they're even (carry your tools in your pocket).
 
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gortnipper said:
Read this thread about why we have balance tubes, and why using a tuning guage in its place shows the effects seen here and is not recommended.

https://www.accessnorton.com/NortonCommando/carb-balance-pipe.16589/
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Thank you. Very interesting and basically the answer to my question. Interestingly it sounds like the balance pipe introduces more air and should have a idle higher than with a manometer connected, which I experience the opposite so guessing running too rich in the idle circuit anyway so more tweaking there.
 
The Brian Slark method is to remove the float bowls and main jet holder. Then you can watch the needles rise together. Adjust until they go out of sight at exactly the same time. Done.
 
milfordite said:
The Brian Slark method is to remove the float bowls and main jet holder. Then you can watch the needles rise together. Adjust until they go out of sight at exactly the same time. Done.
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You can achieve the same by feel with two fingers in the carbs with the air filter off.
 
Beach said:
Here's what I use to sync carbs on all my bikes. Have had mine for over 30 years and use it all the time. Simple and accurate.

www.saber-cycle.com

Mercury Carb Sync Tuner / Adjusting Tool Pkg

Love This : Mercury Carb Sync Tuner / Adjusting Tool Pkg
www.saber-cycle.com
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+1 I have used a Morgan mercury manometer for longer than I care to remember. its extremely simple to use and best of all has no moving parts that require calibration
The setting of needle height by either watching lift, or placing a drill bit under the slide until they pinch is archaic to say the least.
 
gortnipper said:
Read this thread about why we have balance tubes, and why using a tuning guage in its place shows the effects seen here and is not recommended.

https://www.accessnorton.com/NortonCommando/carb-balance-pipe.16589/
Click to expand...

Agreed. I have secondary vacuum take off ports on my manifolds for this reason, to get a reading with the balance pipe in place.

Also important not to confuse slide synch with carb balance, they're not the same thing. Balancing the vacuum between the carbs does not assume the slides will be synched relative to each other, quite often they will not be, based on variances in compression, valve lash, mixture etc.
 
acadian said:
Agreed. I have secondary vacuum take off ports on my manifolds for this reason, to get a reading with the balance pipe in place.

Also important not to confuse slide synch with carb balance, they're not the same thing. Balancing the vacuum between the carbs does not assume the slides will be synched relative to each other, quite often they will not be, based on variances in compression, valve lash, mixture etc.
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Why even bother then?
 
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