Manometer theory

[Orange Guzzi]

Mikuni/Sudco specifies to sync the carbs on a motorcycle with 2 or more cylinder on some of their products with a rod inside the carb throats.  No gauges or balance manometers.  Feeler wires in a set of 27, 28 or 29 smooth bores. 

[Kiwi_Roy]

To answer Tom H,
Using water as an example
The beauty of a "U" tube manometer both ends are roughly at the same pressure so your columns can be relatively short 3 or 4 feet, getting a balance within a few inches is very accurate
If you were trying to measure the manifold pressure or balance using individual manometers referenced to atmosphere your columns would need to be 20 or more feet high, a perfect vacuum is 33.93 feet water column.

[Kiwi_Roy]

Mikuni/Sudco specifies to sync the carbs on a motorcycle with 2 or more cylinder on some of their products with a rod inside the carb throats.  No gauges or balance manometers.  Feeler wires in a set of 27, 28 or 29 smooth bores.

I have to do something similar on my 72 Eldorado, it has no vacuum connections on the manifold so I use a drill bit or Allen key to set both the same.
I don't believe slides are as critical as butterflys

[Rusnak_322]

For $90, they must be some very nice gauges!

The set I bought was in a kit with 2 gauges, hose and all and was about $30, might have been less, can't remember.

Kinda thought that would be the answer. Thanks,
Tom

I was talking about these - https://www.revzilla.com/product/motion-pro-syncpro-carb-tuner?gclid=Cj0KCQjwybvPBRDBARIsAA7T2khmAj_vv61PQNOeqymU1B8kUJfnsGR7_0gosTeJbK6CfnzxM4vjPnwaApSvEALw_wcB

or these - https://www.revzilla.com/motorcycle/bike-master-carburetor-synchronizing-kit


I had never seen the cheap ones, but I just saw these on eBay searching for the Motion Pro kit -
https://www.ebay.com/i/382160869412?chn=ps&dispItem=1

[Muzz]

For really cheap (Guzzi content) I used to tune our twin carbed BMC Mini by using a piece of plastic tubing shoved in to each ear and placed in the throat of each carb. The system worked remarkably well.

[Orange Guzzi]

Ok I'll give you that a service manual might ask you to set at a certain inches of mercury but we don't usually balance the throttle bodies using a service manual, I will have to see what my Griso manual says

No, Volume per inch has nothing to do with it Head is head for 1/4" or 4 inch ID, no difference in the pressure at all.

Inches are inches are inches, pressure is measured in these units because it can be replicated anywhere, It may be effected by the gravitational constant at various points in the globe but that's insignificant, if we are going to worry about that we should also worry about temperature effect.

The i.d. of the vacuum tube along with the liquids SG are factors when assigning a scale to the movement while under a vacuum or pressure.  It takes more pressure or vacuum to push or suck a 4 inch column of water up than a 1/4 inch.  Head pressure accumulates the higher the column of liquid is.  That is why the liquid in balance tubing stops raising, it reaches equilibrium. 

Mercury is a heavy, dense and liquid element (and hazardous).  It was used as part of testing equipment for many years.  A National and World set of Standards were developed around the weight and expansion ratio based on temperature.  When substituting mercury with another liquid of a different SG, the test equipment will not give the same results.   You can balance between two or more intakes, but you will not get the same vacuum reading with the substitute liquid with the test equipment. 

Take a 10 feet long piece of clear tube and a threaded nipple attached to the intake manifold balance hole.  Loop the clear tube up and over the handle bars with the open end at ground level.  Get a selection of liquids of various SG's.  Milk, water, alcohol, mercury.  Start the motorcycle engine.  Place the hose in the various liquids.  You will see that each one will suck up the tube to a different level. 

[Huzo]

Thanks very much guys. There's a lot about that I'd forgotten, or perhaps never knew in the first place. The bet is settled.
(He won)...
I did not think the closed system would work correctly, but all seem to think it will in principle.

[rodekyll]

For really cheap (Guzzi content) I used to tune our twin carbed BMC Mini by using a piece of plastic tubing shoved in to each ear and placed in the throat of each carb. The system worked remarkably well.

It's all fun until someone sneezes and their brains are pulled from their ears.   



I think some confusion is being introduced with the specific vacuum numbers.  We're talking "balancing" intakes.  Balance is a relative term.  It doesn't care what the vacuum is at all.  All it cares about is that the vacuum is even.

When we're talking about an absolute vacuum number (like 18-24" at idle for a Datsun L16) we're looking at the manifold (plenum) pressure, which tells us about the engine's state of tune and compression/leakdown. 

Manifold pressure doesn't care how many intakes the system has.  Balance doesn't care about manifold pressure.  "Balance" should remain pretty much the same throughout the throttle range, regardless of accel, decel, or overrun.  Manifold vacuum changes under each of those conditions, as well as under varying load, RPMs, barometer, etc.  It can be 26"+ on heavy decel, and zero when the engine rpm is stalled going up a hill.  In either extreme (or any point in between), the intake balance should not change. 

[Tom H]

I was talking about these - https://www.revzilla.com/product/motion-pro-syncpro-carb-tuner?gclid=Cj0KCQjwybvPBRDBARIsAA7T2khmAj_vv61PQNOeqymU1B8kUJfnsGR7_0gosTeJbK6CfnzxM4vjPnwaApSvEALw_wcB

or these - https://www.revzilla.com/motorcycle/bike-master-carburetor-synchronizing-kit


I had never seen the cheap ones, but I just saw these on eBay searching for the Motion Pro kit -
https://www.ebay.com/i/382160869412?chn=ps&dispItem=1

The Ebay one looks like what I have. There was a few different vendors with the same item but different prices. I picked the cheapest one.

Tom

[Kiwi_Roy]

The i.d. of the vacuum tube along with the liquids SG are factors when assigning a scale to the movement while under a vacuum or pressure.  It takes more pressure or vacuum to push or suck a 4 inch column of water up than a 1/4 inch.  Head pressure accumulates the higher the column of liquid is.  That is why the liquid in balance tubing stops raising, it reaches equilibrium. 

Mercury is a heavy, dense and liquid element (and hazardous).  It was used as part of testing equipment for many years.  A National and World set of Standards were developed around the weight and expansion ratio based on temperature.  When substituting mercury with another liquid of a different SG, the test equipment will not give the same results.   You can balance between two or more intakes, but you will not get the same vacuum reading with the substitute liquid with the test equipment. 

Take a 10 feet long piece of clear tube and a threaded nipple attached to the intake manifold balance hole.  Loop the clear tube up and over the handle bars with the open end at ground level.  Get a selection of liquids of various SG's.  Milk, water, alcohol, mercury.  Start the motorcycle engine.  Place the hose in the various liquids.  You will see that each one will suck up the tube to a different level.

On point 1
You are totally WRONG its inches of mercury not square inches of mercury of inches of mercury per square inch, sorry you don't understand pressure.

On point 2
I'm not disputing that, a 3 ft mercury manometer re-filled with water won't be able to measure the same range but it will be just as accurate over a shorter span.
Mercury is still used but you see it less and less.
I went to great lengths to talk our members out of using it, a mercury manometer is a liability.

On point 3
I'm trying to wean my Guzzi off milk and alcohol LOL
all those light fluids would disappear down it's throat so fast if I did that.

Anyway I don't think there is much point in continuing this debate, you think you are right, I know I am
Cheers
Roy

[Orange Guzzi]

On point 1
You are totally WRONG its inches of mercury not square inches of mercury of inches of mercury per square inch, sorry you don't understand pressure.

Funny, I need new glasses or a bigger screen.  Thanks for correcting my typing error.  I know you cannot read my  mind, but that is what I was trying to type out.  I though I went back and corrected my original comment.  If not, thanks for pointing it out a second time. 

The inch of mercury (inHg) is defined as the pressure exerted at the base of a column of fluid exactly 1 inch (in) high, and the fluid density is exactly 13.5951 gram per cubic centimeter (g/cm�), at a physical location where the gravity acceleration is exactly 9.80665 m/sec�.  1 inch of mercury = 13.5951 inches of water.  In other words, two mercury gauges can be 1 inch difference and two gauges filled with colored water would be 13.595 inches difference.   That is why the SG of the liquid is critical to the accuracy.  Someone could spend a lot of time trying to get a balance set up when in fact they were actually very close if the two levels were 6 inches different with a low SG liquid/colored water.

On point 2
I'm not disputing that, a 3 ft mercury manometer re-filled with water won't be able to measure the same range but it will be just as accurate over a shorter span. 
Mercury is still used but you see it less and less.
I went to great lengths to talk our members out of using it, a mercury manometer is a liability.

On point 3
I'm trying to wean my Guzzi off milk and alcohol LOL
all those light fluids would disappear down it's throat so fast if I did that.

Anyway I don't think there is much point in continuing this debate, you think you are right, I know I am
Cheers
Roy

I did not see any debate in your comment or who is right or wrong.  Just a correction of my ounces to inches.  Please continue on with your tutoring.  I like to learn. 

Just because mercury  gauges were the tool of choice does not mean they  are still the tool of choice. The new configuration of vacuum gauges are much safer for the user.  Especially since milk, alcohol, mercury, water or other liquids are not being sucked thru the engine and blown out the exhaust.   Trying to replicate them with hardware store supplies is not an accurate way to "tune" an internal combustion engine.   Especially if the tool has not been calibrated to the "inches of mercury" standard.     A visual setting of the butterflies or carb slides would be just as accurate as a non calibrated assembly of hardware store parts.   

If you are going to sync intakes, buy real gauges of your choice, use gauge wires or visually set the balance.  The SG of the fluid is critical in a wet set up, the denser, the better and the ability to meter the vacuum flow is critical to prevent pulses/bouncing. 

[n3303j]

  It takes more pressure or vacuum to push or suck a 4 inch column of water up than a 1/4 inch. 

Pressure (or vacuum) is PSI. Increase the diameter of the column and you increase its surface area. A Mercury column in a manometer will sit at about 31 inches, held in place by atmospheric pressure whether the column is 1/8 inch in diameter or 1 inch in diameter.

[Orange Guzzi]

Pressure (or vacuum) is PSI. Increase the diameter of the column and you increase its surface area. A Mercury column in a manometer will sit at about 31 inches, held in place by atmospheric pressure whether the column is 1/8 inch in diameter or 1 inch in diameter.

I was referring to the weight of the total column of water, not external pressure.  Water at ground level has more pressure on it than water at the top of the water tower. 

A piece of tubing with 1 inch of mercury in one side and 13. 6 inches of water would be balanced in the center at the bottom.  Big difference in SG. 

[n3303j]

I was referring to the weight of the total column of water, not external pressure.  Water at ground level has more pressure on it than water at the top of the water tower. 

A piece of tubing with 1 inch of mercury in one side and 13. 6 inches of water would be balanced in the center at the bottom.  Big difference in SG.

Pressure measured at the bottom of a ten foot high column of water will read the same number of PSI whether the column is 1 foot in diameter or 100 foot in diameter.

In balancing carbs (throttle bodies) all we want to do is eliminate any differential vacuum. A U tube is very sensitive to pressure differentials. Doesn't matter much what the fluid is. I use ATF because it is visible, cheap and doesn't hurt anything if it gets sucked through the engine. Been balancing  BMW, Ural & Guzzi engines this way for years. It gives a strong visual response to the tiniest turn of an idle stop or throttle cable jacket adjuster. Balance at idle with slack in throttle cable. Second balance at 3K RPM by tweaking cable adjusters.

[Huzo]

So now that most of it has been said. Can I safely assume that a manometer filled with a suitable fluid can be used to balance carbs or TB's where applicable?
It seems so...

[n3303j]

Yes. (For the U-Tube device)
Not to be confused with You-Tube.

[Huzo]

Yes. (For the U-Tube device)
Not to be confused with You-Tube.

Oh, ok.....
Thanks.

[mtiberio]

gauges? only as good as the calibration
mercury? I got rid of my mercury manometers once the kids arrived
I use the differential method, I tape a 3' "U" of clear hose to a yardstick that I hang from the garage rafters. I run the 2 ends of the hose to the manifolds. I use 2 Stroke Premix Oil, that way if it gets sucked into the motor no problem.

Yes the oil is inferior to the mercury. Its hard to get the levels even, and as others have said anything close if probably good enough given the increased sensitivity of oil vs Hg.

[Chuck in Indiana]

You guys are beginning to scare me. I still have my old mercury carb sticks from a generation ago. Should I really ditch them?

[Kiwi_Roy]

I wouldn't but I'd retire it for something safer especially if the Grandkids are hanging around the shed. Mercury has a fascination for kids, eventually it gets dropped on the floor. One drop on the floor will send a mercury vapour analyzer up scale.
I wonder what the EPA would say?
We come from the era when they put it in your teeth, did we go crazy eh!

 

[Rough Edge racing]

I wouldn't but I'd retire it for something safer especially if the Grandkids are hanging around the shed. Mercury has a fascination for kids, eventually it gets dropped on the floor. One drop on the floor will send a mercury vapour analyzer up scale.


Sent from my shoe phone!

 Use the air flow device I mentioned, if it will fit on your bike ....The German made version is about 50-60 bucks...No hoses, no mercury, no liquid, works upside down....

[Wayne Orwig]

I have one of those. works great IF you have the intake manifolds off.

https://www.summitracing.com/ga/parts/edl-4025/overview/

[Rough Edge racing]

I have one of those. works great IF you have the intake manifolds off.

https://www.summitracing.com/ga/parts/edl-4025/overview/

 What you show is not the tool I mentioned......But as you say, access to the carb bellmouth. velocity stack or throttle body is required

[Huzo]

Do I recall when the Doctor (not Rossi), used to stick mercury thermometers in your mouth?
Our pet cat was lucky(er), he used to cop it in the other end!

[Kiwi_Roy]

Do I recall when the Doctor (not Rossi), used to stick mercury thermometers in your mouth?
Our pet cat was lucky(er), he used to cop it in the other end!

Not the same one I hope, or were you always first?

[Huzo]

Not the same one I hope, or were you always first?

Lucky (for me), I was first..
The cat used to balk a bit, after he knew it'd been in my gob !
I wouldn't have taken the risk with it inserted that far south, if it broke, imagine if Mercury collided with Uranus !!!
What a show....

[Chuck in Indiana]

I wouldn't but I'd retire it for something safer especially if the Grandkids are hanging around the shed. Mercury has a fascination for kids, eventually it gets dropped on the floor. One drop on the floor will send a mercury vapour analyzer up scale.
I wonder what the EPA would say?
We come from the era when they put it in your teeth, did we go crazy eh!

My cousin was in dental college when I was a pup and he brought me vials of mercury to play with.  Sure, I have it in my teeth.
I'm just wondering *just* how dangerous it is to have the carb sticks out in the Guzzi Garage. (tm) No grand kids around, etc.

[Kiwi_Roy]

I would say not dangerous at all, perhaps the equivalent to having a bunch of Ammo on the shelf.
Even if you have a spill it can be cleaned up, make sure the hoses are in good condition. We used to put a drop of oil on top of the mercury, the thought being it stops the Hg evaporating.
I'm sure the chances of you having a spill are pretty remote.
Would I recommend it for a new purchase, No
Enjoy using it.

Spill prevention
Sometimes you see a float valve at the top of each column, just a cork that slams shut if the mercury gets past the top for example if one hose drops off.
On others I've seen a small tank on each line big enough to hold the contents and then some.

Other sources of Mercury in your home
Flourescent lamps - Both the usual long variety and the globe style, the mercury vapor conducts the electricity to make the coating inside the tube fluoresce
Thermostats - the older heating system thermostats had quite a bit inside
Thermometers - I'm not sure if they still sell these or not, I see a lot of digital ones.
Batteries

[Chuck in Indiana]

Thanks, Roy..