TB balancing options/questions

[tris]

A) My Carbmate appears to leak one side. If I pull a steady vacuum (suck on the 2 pipes  ) one side will drop away.
    Has anyone else experienced this and if you did did you manage to fix it.     PS I have given it a clean?

B) As a result of A above I'm think of make one from a 4 foot stick and a bunch of tubing. Just one question. why do people recommend ATF as opposed to water given that water is denser than oil?
    I was thinking of water PLUS food colouring so I can see it PLUS a splash of washing up liquid to minimise the meniscus 

[Old Jock]

Be interested in this too as I've been trying to evaluate what would be the best tool for the job

The only reasons I can think of ATF is some of them are already colored and I'm not sure about viscosity properties, if ATF is higher it may introduce some damping.

Some bikes can cause carb sticks to really bounce if the idle is low and I'm going to try a little experiment with a glass tube filled with cotton wool or the like in series to see if it helps damps the pulses making it easier to read

[yogidozer]

Tris, I don't think water, or ATF is a good idea. Every "stick" I've seen uses mercury. Heavy liquid, likely used to keep pulsing from messing you up.

[tris]

OJ
The Carbtune comes with 2 orifice tubes  that you have to fit before use. Up until now its been good, so I'm a bit nonplussed at the moment

Yogi
You're quite correct - but Mercury is banned to prevent us becoming as mad a hatters!!

[yogidozer]

OJ
The Carbtune comes with 2 orifice tubes  that you have to fit before use. Up until now its been good, so I'm a bit nonplussed at the moment

Yogi
You're quite correct - but Mercury is banned to prevent us becoming as mad a hatters!!

thought it might, my sticks have been around for awhile 

[Kiwi_Roy]

I have just finished reading a book "Keepers of the Light" by Donald Graham about the lighthouses around the coast of British Columbia
What the hell has that got to do with carb tuning? I hear you ask.

At several points in the book he goes on about the harmful effect of Mercury, I quote
"The beacons were the culmination of four centuries of British Lighthouse technology, their mantles and reflectors floated on a tub filled to the brim with mercury...... The primitive though highly effective use of mercury posed a sinister threat. Even today Doctors can misdiagnose mercury poisoning as rheumatism, senile dementia, emotional instability, or psychosis. Whether it was absorbed through the skin or entered the lungs, metallic mercury wound its way through the central nervous system to the brain, short-circuiting the processes of emotional response and rational thought. Silent, insidious, incurable, its effects compare in their severity to long term exposure to radioactivity"...... he then goes on to describe how the keepers had to wipe off the surface and strain it through chamois leather.

Its use is banned in many European countries, I'm sure it will be in North America before too long,  last I heard you had to vent mercury manometers outside.

Ask yourself what's the least harmful fluid to get accidentally sucked into the engine, certainly don't want to vapourize mercury, Water or ATF are probably ok.

If you want to measure the difference between two pressures then use a differential pressure gauge
I use engine oil in my manometer, it's viscosity provides damping (I don't have needle valves)
I'm sure ATF has other advantages

[Old Jock]

It shouldn't make any difference what fluid you use with the caveat the less dense the fluid the bigger the manometer will have to be.

From off the top of my head Hg is more sensitive or less damped than almost anything else, I read somewhere Hg is the only fluid that doesn't wet glass, so little to no drag from the tubing on the fluid, the reason it would "dance" less is because 1"Hg is a far higher pressure than 1"H2O.

I'm aware of the orifice fitting, but the tubes can still dance. This is why I was thinking of an restrictor followed by a larger chamber with cotton wool or the like to dampen the pressure waves further.

I have some Hg and was thinking of making my own from either glass with a rubber or plastic piece forming the "U" or all plastic tubing.

It would all have to be thick walled and have valves and caps to seal it when not in use, needle valves would be the best I think to act as a variable orifice.

The manometer would then be stored in a shed to prevent anybody coming into frequent contact with Hg vapour.

There used to be an electronic one sold at a reasonable price but the inventor passed away, then the transducers became unavailable, pity because that was fantastic piece of equipment it gave a very steady reading, but I don't know if the damping was done physically or calculated in the electronics

The other electronic offerings I know of are either not very good or stupid money

Interested to see what Roy has to enlighten us with 

[acogoff]

    The ATF is easy to see with old people (Guzzi Owner) eyes and if one side is way off you are not pulling H2O into the engine, not that that would hurt all that much. I have my 3 FT. "stick-O -tubes" filled about 1/2 full and works OK at that level.

[Wayne Orwig]

ATF is a good color to see. Is more viscus so does not splash around. And does not evaporate. Under the vacuum, the water may easily got evaporated.

[Kiwi_Roy]

I have some Hg and was thinking of making my own from either glass with a rubber or plastic piece forming the "U" or all plastic tubing.

Don't get me wrong, I like mercury manometers, they are extremely accurate and can be made reasonably safe but in this case we aren't so interested in the pressure as in the difference in pressure so why not use something lighter with less responsibility, oil will travel further up the tube by a factor of ~15.
In the Instrument shops we used to put a couple of drops of oil on top of the mercury the thinking being it provided a barrier between the mercury and atmosphere.

BTW if you spill mercury sprinkle flour of sulphur around it will amalgamate with the mercury making it easier to sweep up.

[Kiwi_Roy]

If you want to make your own electronic version DIgikey have hundreds of different DP transducers  in the $10-15 range that could be supplied with 6 Volts and read with a multimeter
I would start with something like an MPX2300DT1 0 - 40 kPa

https://www.digikey.com/products/en/sensors-transducers/pressure-sensors-transducers/512?k=&pkeyword=&v=568&FV=3680004%2C1f140000%2Cffe00200&mnonly=0&ColumnSort=1000011&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25
Look for one with a minimum quantity of 1 and psi range of around 5-7 psid with an output you can read with your meter,

[rodekyll]

The liquid doesn't matter as long as you can see it and don't mind if it accidently gets sucked into the engine.  It cannot escape the tube unless only one side is attached while the engine is running or one side has no vacuum.  The liquid is caught in a tug of war between the two spigots

Make your balance tube with 15' of clear plastic 1/4" tubing, a plastic "T" barb, 4' board (I used a piece of old fake wood flooring), wire staples, a couple of drywall screws, a 1/4" plug and a yardstick.

Fasten the yardstick on the board, centered.

Cut the tube in half and rejoin it with the "T". 

Put the "T" at the bottom of the yardstick and staple the tube up both sides.  Make the staples loose and the extra length neat.

Inject your fluid (I used power steering fluid, but anything you can see in the tube and don't mind accidently getting sucked into the engine will work) into the tube through the open leg of the "T" and cap it.  I made a 10" column up each side and used my brake fluid irrigation syringe to inject it.

With the engine OFF attach a tube end to each TB spigot.  Prop up the gauge somewhere handy.  The more vertical the better.

Start the engine.  The TB vacuum will pull the liquid both directions.  The side with more vacuum will pull harder.  The difference will be easily seen in the tube.  Adjust till balanced, and there you go.  If you have trouble seeing the liquid, an LED flashlight will help.  If you still have trouble seeing it, the problem is not the tool.

GUZZI CONTENT:  I made mine with stuff lying around - $0.00 invested.

[Kiwi_Roy]

Exactly 
The most accurate DP gauge money can buy.

[tris]

If you want to make your own electronic version DIgikey have hundreds of different DP transducers  in the $10-15 range that could be supplied with 6 Volts and read with a multimeter
I would start with something like an MPX2300DT1 0 - 40 kPa

https://www.digikey.com/products/en/sensors-transducers/pressure-sensors-transducers/512?k=&pkeyword=&v=568&FV=3680004%2C1f140000%2Cffe00200&mnonly=0&ColumnSort=1000011&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25
Look for one with a minimum quantity of 1 and psi range of around 5-7 psid with an output you can read with your meter,

Cheers Roy - I was looking at the same thing last night but didn't know how to read it.

Do I just put the multimeter across the output and earth and the voltage can be plus or minus?

[tris]

This is what I was looking at Roy if it helps with your deliberations

https://m.ebay.co.uk/itm/New-APM2-5-MPXV7002DP-Airspeed-Breakout-Transducer-Differential-Pressure-Sensor-/201960081889?nav=SEARCH

[Kiwi_Roy]

Yes, this one has a board and some extra components, if you put your multimeter across Output and earth it will read about 2.5 Volts with no pressure dropping towards zero (0.5) as the pressure goes negative going towards 4.5V as the pressure goes positive.
If you want it to go +/- with zero as the mid point just make a Voltage divider from Vs to GND with a couple of 1k resistors in series or use a 1k to 5k trimpot. Use the mid point for your meter negative.
That transducer calls for a 5V supply I suspect that's just to meet the accuracy spec, a 12V to USB adapter would be a good source of 5 Volts,
I'm fairly sure it would operate on 4 AA cells
Using a trimpot will allow you to zero the meter without pressure.

The bare MPX sensors (without circuit board and extra components) have 4 terminals, 2 for supply and 2 for the meter, their specs calls for 3 to 6 Volts Vs.

If you look for the part No on Digikey they have handy Data Sheets

[pete roper]

Morgan Carbtune. Inexpensive. Clean. Accurate. Robust. Safe.

[Wayne Orwig]

Cheers Roy - I was looking at the same thing last night but didn't know how to read it.

Do I just put the multimeter across the output and earth and the voltage can be plus or minus?

And the needle on the voltmeter will likely slam from one end to the other. It will probably need a filter added to dampen the variation. A regulator may be required.

[Kiwi_Roy]

Wayne's right a restrictor and small capacity tank in each leg, I would have chosen a DP cell of at least 7 psid
Note in my post No 10  I suggested a model of 40 kPa , the one you are looking at is only 2 kPa (8" WC) -too sensitive

 

[Kiwi_Roy]

Tris, is the carbamate a liquid filled manometer?
If so the only reason one side would drop away would be an air leak, perished tube perhaps.


Sent from my shoe phone!

[tris]

Roy it uses metal rods in closely fitting tubes

I wrote to Carbmate yesterday and got some options back  to try - watch this space once I've tried them

[Kiwi_Roy]

I have never studied a carbtune to understand exactly how they work I.e . why don't the rods fly to the top, is the tube tapered or something?


Sent from my shoe phone!

[Old Jock]

I have never studied a carbtune to understand exactly how they work I.e . why don't the rods fly to the top, is the tube tapered or something?


Sent from my shoe phone!

Unless I've missed something Roy no, they are just metal rods, it's akin to pulling Mercury, I'm not 100% but they must be open to atmosphere at the bottom with tight clearance between rods and tubing. As pressure reduces in the top atmospheric pressure pushes the rods up the tube until it's counterbalanced by the force caused by the pressure differential.

Pretty sure there will be leakage between rod and tube but they probably factor that in

At least that's my understanding

[Wayne Orwig]

Mercury weights more as more mercury is pulled out of the supply. Until the volume/weight of mercury equalizes with the suction.
A rod weighs the same at the bottom as it does at the top. There is nothing to equalize in that respect.

[Old Jock]

Of course Wayne

Stoopid Stoopid Sttopid , Engage Brain before posting  

I wonder then if it has something to do with friction between rod and tube increasing as its pulled upward

[rodekyll]

The old Bosch K-Jetronic EFI was a constant injection system that worked on a "rising body" principle.  A disk is situated in the throttle body bore similar to a closed butterfly.  However it is attached to a centerpoint instead of an axle, and the centerpoint is attached to a slotted fuel leak.  It has a peculiar shape that allows intake air to get underneath it.  As more air flows, the disk rises, pulling the slotted body upward, exposing more of the slot's length and therefore allowing more fuel to the injectors. 

CV carbs also work on this principle -- the butterfly allows more air to flow and the piston rises in response to the pressure differential.

And I have a carb synch tool called a "unisync" that has an adjustable venturri.  The greater the pressure differential through the venturri, the higher a little ball floats in a vertical tube.

I suspect this is why OJ's rods work.

[Kiwi_Roy]

Mercury weights more as more mercury is pulled out of the supply. Until the volume/weight of mercury equalizes with the suction.
A rod weighs the same at the bottom as it does at the top. There is nothing to equalize in that respect.

That was my thinking, I just couldn't express it so well.
So we still don't know why it doesn't shoot to the top, David may be on to something.

My theory
The rod is a close fit for a few inches at the bottom but further up the tube has a greater clearance, the friction force between air and rod gets less and less as it rises out of the close fit area.

My sketch shows quite a step between the lower and upper diameters but in reality it might just be a thou or 2
Also as the rod rises out of the close fit area the pressure drop required to pass by the rod becomes less.
The pressure (atmospheric) below the rod remains the same but the pressure difference drops.
I'm guessing there's flow restrictors in the lines to the carbs.
That must be it.

[tris]

They have long but light weight spring and the vacuum pulls the rod up against the spring

HTH 

[Kiwi_Roy]

They have long but light weight spring and the vacuum pulls the rod up against the spring

HTH 

Ok that explains it, I'm happy now 

[Orange Guzzi]

1 inch of mercury = 13.5951 inches of water.  This means that a mercury gauge can indicate a 1/2 inch difference if compared to a gauge with a low specific gravity fluid (SG) such as colored water, which could be over 6 inches difference. 

Also, the pulsing of the intake  will cause the cavitation or bubbling in the lower SG fluids.  Vacuum gauges with a diaphragm and flow control is the best set up.  Clean and safe. 

If you were to make a setup with low SG shop fluids and get a fluid level at each tube withing 6 inches while connected to the running bike, I would say you are extremely close to balanced.