Carb Synch Question

Beach said:

Why even bother then?

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I assume you mean synching the mechanical position of the slides? I think for "basic" running it's a good enough starting point, and on an otherwise healthy motor will get you in range which, for most people, is probably good enough. But my experience with Norton owners is that good enough is usually never enough... hence our constant fettling

That makes sense. I'm not one to over think things. Try to keep it simple if running correctly, never strive for perfection on these old bikes.

FWIW
always set your timing first,
adjust you valves,
always adjust carbs last

Gee where did I see this before?

Everything is based on the assumption of a competent and accurate procedure.
This assumption must be trusted or yes...WHY BOTHER

acadian said:

Also important not to confuse slide synch with carb balance, they're not the same thing

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True A slide sync is a pre running adjustmant to allow an initial fire up of the engine and nothing more.

With the pre carb tune done, and assumed the final carb adjustment with ACCURATE vacuum gauges (mercury stix) will be the final setting of equal flow.
This final adjustment IS the synchronizing and adjustment of the engine side of the slides receiving equal manifold partial ambient pressure.
The two cylinders are physically connected and do not/can not run at different speeds regardless of which side is or IS NOT pushing the crank more than the other.
The final air flow synchronization disregards any real or imagined cylinder differences to try and supply both cylinders with the same partial pressure filling.
Only when the engine is under load does it actually draw a significant amount of air and the side to side imbalance while just only reving the engine will not create a vacuum/partial pressure worth adjusting.

If the owner has gone to the lengths of installing a Madass unit carb manifold, then why ever not?
With the unit fitted you have the ability to get left and right cylinders vacuum draw in perfect alignment
Interesting to read on the thought of testing with and without balance pipe fitted..I have only set mine with the pipe removed, I will now "Tee" off the balance pipe to check again

dynodave said:

With the pre carb tune done, and assumed the final carb adjustment with ACCURATE vacuum gauges (mercury stix) will be the final setting of equal flow.

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Please correct me, Dave, if my logic is flawed. Carb balancing with vacuum gauges is done at idle where vacuum is highest, yes? And the adjustment is done using the idle speed (stop) screws. It would seem to me that once the carbs have been adjusted for equal vacuum that they are no longer "in sync" and will not be at the same height in the bores under throttle. Does the "balance" follow at throttle positions other than idle?

maylar said:

Please correct me, Dave, if my logic is flawed. Carb balancing with vacuum gauges is done at idle where vacuum is highest, yes? And the adjustment is done using the idle speed (stop) screws. It would seem to me that once the carbs have been adjusted for equal vacuum that they are no longer "in sync" and will not be at the same height in the bores under throttle. Does the "balance" follow at throttle positions other than idle?

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The Norton equipped with the splitter cable design is never going to be that accurate
But with a common manifold design using piano wire lifters the adjustment screws are redundant and a very good level of accuracy achieved.
I set mine at 1200 rpm, took to revs up to 3500rpm and the balance was still within a centimetre of mercury
Even on my T160 which uses a common manifold the shop manual says use a 1/16 drill to set the slide height. This was an excellent opportunity for Triumph to put take off points in the intakes to use gauges...but they diddnt
I drilled and tapped mine years back an I have a 750-800 ish tick over all the time

To be in tune with how an engine runs, you are correct the idle circuit, being separate, though still subject to timing and mechanical proper preparation and condition are also a big mass of mechanical components and the variables of the machined componet and settings are last to be "tuned" and synchronized.
Now to additionally repeat the process for the second half of the carb...the high speed circuit,
The idle screws are only for the idle mixture at the before and after hole at the slide. This includes the idle speed screw. Now each side is making each 1/8hp and behaving nicely at the idle resting point.
Moving on to a whole new world is where you ask both carbs to control the flow of each cylinder like each is a horse power or 10. This is totally with the same crappy sloppy slides and all the other haphazard machined components.
Two different procedures for controlling two chipmunks at idle or two frisky horses on the run.

olympus said:

The Norton equipped with the splitter cable design is never going to be that accurate

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totally disagree
Balancing for RPM 's when unloaded does not make competant adjustment I doubt you are running even on the needle jet or main jet .
1 CM difference bad bad bad....

maylar said:

Please correct me, Dave, if my logic is flawed. Carb balancing with vacuum gauges is done at idle where vacuum is highest, yes? And the adjustment is done using the idle speed (stop) screws. It would seem to me that once the carbs have been adjusted for equal vacuum that they are no longer "in sync" and will not be at the same height in the bores under throttle. Does the "balance" follow at throttle positions other than idle?

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The carbs are balanced at idle on the throttle stop screws
Then on the cable adjusters above idle
The transition is important to get right, you need to micro adjust the cables at this point
It's also best to cable tie the cable splitter to the frame
Or fit the madass gantry

baz said:

The carbs are balanced at idle on the throttle stop screws
Then on the cable adjusters above idle
The transition is important to get right, you need to micro adjust the cables at this point
It's also best to cable tie the cable splitter to the frame
Or fit the madass gantry

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Pretty much agree 95%
As a old remedy for crappy cables and the 2 splitters and all the wires and clutch cable making a bit of a trafic jam under the tank.
I now make my own cables and have a rigid formula that works excellent IMO.

My throttle cable always comes in to the left side of the steering neck, therefore the splitter stays on the left. My RH lower throttle cable I make an inch longer so it will cross over with out pulling everyting out of shape.from the strain.
I repeat the same thing for the choke and it comes in the RH side of the neck. Same process but mirror image.
The lower choke cable for the LH choke I make an inch longer and cross it over.
The splitters lay nice and straight and parallel with the back bone.
Now the throttle and choke cables arc in a nice smooth bow down to both of the carbs .
I started this process way back in the 90's when I bought genuine AN (BSA regal) cables and they were not right and I then had to make my own from scratch.

I don't have the equipment (yet) to test under load, FWIW I use a carbtune gauge as the final step (after mixture is set), setting the idle balance with stop screws and off idle with the cable adjusters (on the triumph and beezer). With the madass gantry both states are adjusted via the cable adjusters at the top, the idle stop screws in the carb are backed all the way out

dynodave said:

To be in tune with how an engine runs, you are correct the idle circuit, being separate, though still subject to timing and mechanical proper preparation and condition are also a big mass of mechanical components and the variables of the machined componet and settings are last to be "tuned" and synchronized.
Now to additionally repeat the process for the second half of the carb...the high speed circuit,
The idle screws are only for the idle mixture at the before and after hole at the slide. This includes the idle speed screw. Now each side is making each 1/8hp and behaving nicely at the idle resting point.
Moving on to a whole new world is where you ask both carbs to control the flow of each cylinder like each is a horse power or 10. This is totally with the same crappy sloppy slides and all the other haphazard machined components.
Two different procedures for controlling two chipmunks at idle or two frisky horses on the run.



totally disagree
Balancing for RPM 's when unloaded does not make competant adjustment I doubt you are running even on the needle jet or main jet .
1 CM difference bad bad bad....

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OK so why Is within 1 cm/HG bad.... my manometer kit states this is what You should be setting between the red lines on the scale which are set at 1cm. But I always try to achieve a better level of accuracy as low as possible., hence within 1 CM/Hg
Yes this is a generic kit, And i appreciate your the Magi ,so what level of accuracy should I be setting too??

dynodave said:

My RH lower throttle cable I make an inch longer so it will cross over with out pulling everyting out of shape.from the strain.
I repeat the same thing for the choke and it comes in the RH side of the neck. Same process but mirror image.
The lower choke cable for the LH choke I make an inch longer and cross it over.

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This is brilliant. I wish I had the skills and resources to make my own cables.

Here's what I did.
Reverted back to what I did back in the 70's as a Kid in my 20's.
Boyer at 31, 6/8 valve lash, float levels equal, sync slides.
Fire it up, adjust idle and air screws @ 1 1/2.
Adjust idle up.

Pull left plug, fine tune air and idle to 1k on Rt side.
Reinstall plug wire, idle goes up.
Pull Rt. plug, engine dies.
Adjust throttle stop screw on left until 1k idle.
Fine tune air screw and idle to 1K

Reinstall plug wire, idle way up to approx 1800.
Back off idle screws 1/4 - 1/8 at a time till nice idle.

Slides are now out sync as the left slide is higher.
Adjust cable tops for sync.
Slides do pull all the way up, on full throttle, but the left is a little higher throughout.
Final air screw setting Rt. 1 1/2, Lt. 1 7/8.
Obviously the Rt side was pulling harder on idle.
Compression on each BTW is 175 - 178.
But now, the bike starts easily, idles and runs great.

Ok, now tell me what I've done wrong.

Eric Bauer said:

Hi guys -

So I bought a digi sync carb tuner - it was pretty cheap and frankly, I've balanced carbs the old fashioned way but I'm kind of tired of it. This was similar to biasing tube guitar amplifiers - get the process but wouldn't mind speeding it up. I find when I have the carbs on my 73' 850 perfectly balanced it vibrates way less at all rpms ranges and rides much smoother. Anyway i hooked it up in place of the balance tube and dialed everything in at around 1,000 rpms (after a 20 mile ride so warmed up). Pretty slick me thinks. Then I put the balance tube back on and fire it up and it runs beautifully but is idling at around 500 rpm?? So obviously the balance tube is effecting. So i crank the idle back up to 1,000 as evenly as possible but it's still rougher than it was. Then I connected the machine again and it's idling at 1,350 which makes sense but way too high clearly. I then resynched them at that speed, put the balance tube back on and in business at 1,000 rpm idle. Can someone explain to me what happened. Is there a better way to go about it? Thank you

http://thedigisync.com/digi-sync-top-page.html

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@Eric Bauer Where'd you net out with the Digi Sync? I've been thinking of getting one as well, having come across a video today. Did you end up determining the best way to utilize the tool?

Ronnie said:

@Eric Bauer Where'd you net out with the Digi Sync? I've been thinking of getting one as well, having come across a video today. Did you end up determining the best way to utilize the tool?

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Ronnie,
Also look at the CarbTune out of the UK that is available here in the US.It is a nice unit.
Mike

YING said:

Ronnie,
Also look at the CarbTune out of the UK that is available here in the US.It is a nice unit.
Mike

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Very happy with the Morgan CarbTune. Simple, no fussy high tech gizmos. Ran me about $80 direct from UK. Available in two or four cylinder models.