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...wonder about what will happen to all the equipment (and the knowledge to use it and interpret it) that you have the day you die...

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Originally Posted by reverb
...wonder about what will happen to all the equipment (and the knowledge to use it and interpret it) that you have the day you die...
Ah, rather than a usual Britbike question about what spark plug gap to use, one that explores mortality and the meaning of life.

'Life's a bitch, and then you die'.
Unk.

I'm afraid the answer to what will happen to most of the equipment in the garage is easy. Despite a fairly serious effort on my part to document what I have, what it's used for, and what it's worth, my daughters' initial reaction will be that they need to rent a dumpster. I've also managed to assemble what is likely the world's largest private library of English-language motorcycle books, so they'll have all 5 tons[*] of that to deal with as well. Since they're both educated people, disposing of books will cause them to think more deeply than when disposing the contents of the garage.

[*]If an average book weighs 3 lbs., the total library is actually well over 10,000 lbs.

As for knowledge, some of my historical knowledge will remain in the books written for the Guggenheim 'The Art of the Motorcycle' and Brisbane 'The Motorcycle: Design, Art, Desire' exhibitions. Although I've given a number of public lectures on motorcycle design, magneto troubleshooting, and the physics of carburetors, it's a safe assumption that much of that knowledge went in one ear and out the other.

[Linked Image]

Some of my motorcycle-related technical knowledge will remain in a few articles I've written in the AMHF 'The Antique Motorcycle' magazine and for The Materials Research Society. Also, some of it will remain on the web, here on Britbike and on the VOC forum, at least for as long as those sites remain active. However, despite the wonders of the www, sites come and go so books remain the only truely archival medium (thermonuclear war notwithstanding, of course). So, the reality is, most of it that doesn't already exist in books written by others likely will be lost. Sigh...

That said, I've spent a considerable number of hours the past four months drafting a technical book that's somewhat in the spirit of Radco's 'The Vintage Motorcyclists' Workshop,' but different. However, I'm only about halfway through the material I want to cover and haven't approached potential publishers yet, so they might reject it as too specialized for today's book buyers (of whom, there aren't many left...). If that happens, I'll self-publish it, since that's now an option for material that's too specialized for commercial publishers. Like, say, a book for potential Gold Star buyers. In this vein, very recently David Dunfey self-published a wonderful 475-page 'Building a Competition Vincent Single Cylinder: Racing a 1950 Vincent Grey Flash', containing a wealth of invaluable information that otherwise would have been lost (he's a member of Britbike so can be contacted via a PM).

Although self-published books like these don't have as wide of a distribution as ones from commercial publishers, they ensure the knowledge contained within them is archived for the future. I should add that, if someone is motivated by money, writing a highly-specialized motorcycle-related book certainly is a waste of time since the potential audience is so small.

Tachometer:

A tachometer deserves to be mentioned, although I don't have a tachometer as such to use in the garage because I've never seen a need for one. Although several meters have the ability to measure frequency in the right range, I adjust the idle on carburetors by ear to an rpm that sounds "right."

Aircraft have two magnetos, with an important test of function being to see if the rpm drops beyond an acceptable value if one is switched out. An analogous test on a multiple-cylinder engine would be to see if the rpm dropped by more if the coil on one side of the engine was disconnected than on the other. But, doing such a test without shocking yourself and/or risking damage to the coils isn't easy, with the added uncertainty of the effect on rpm of the different carburetors on dual-carburetor machines. Rather than such an "rpm" test on a twin-cylinder machine, the electrical tests of the coils themselves that I do ensure that both are operating well.

Anyway, although I've never seen the need, I'm prepared to stand corrected if someone points out some important diagnostic test I should be running, but that is impossible without a tachometer.

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Originally Posted by reverb
...wonder about what will happen to all the equipment (and the knowledge to use it and interpret it) that you have the day you die...
The community hasn't decided whether to construct a Khufu scale pyramid or stage a Viking funeral using a decommissioned aircraft carrier.


1970 T120R - 'Anton'
1970 Commando - 'Bruno'
1967 T120R - 'Caesar'
1968 Lightning - 'Dora'
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Originally Posted by reverb
...wonder about what will happen to all the equipment (and the knowledge to use it and interpret it) that you have the day you die...



MMan modestly thinks that some of the information he imparts at a talk goes in one ear, and out the other, and I would have to agree, having attended a decent number of his talks over the years. Sometimes, however, it goes in one ear, rambles around the brain, and then prompts an involuntary verbal response in the listener.

Two decades ago, MMan was giving a talk about his research on motorcycle magnetos to a large crowd of enthusiasts at the Irish National Rally. During the talk, MMan introduced some then quite novel ideas about old motorcycle magnetos, including, for example, the following: "the OEM capacitors in your magnetos are probably close to dying, if they haven't already died".

Among the listeners was a man who wrote the technical advice column in a British classic bike magazine. At the end of the talk, the learned journalist waited for the applause to die down before raising his hand. MMan turned to the man, expecting a question. Instead, the man said, "I have been working in this business for over thirty years, and that's the greatest load of bollox I have ever heard". He then stormed out, while the rest of the crowd fell around laughing, appreciating the journalist's comic timing, if not his genius.

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Originally Posted by NYBSAGUY
Among the listeners was a man who wrote the technical advice column in a British classic bike magazine.... the man said, "I have been working in this business for over thirty years, and that's the greatest load of bollox I have ever heard".
Continuing in that tradition, the latest-to-me (but several months delayed) copy of a British classic bike magazine arrived yesterday, in which the contemporary counterpart of that guy advised a reader to fix his broken front brake cable mounting stud with Lumiweld® solder. First, despite its name, it's only solder. Second, Lumiweld® is difficult to apply because of the oxide so likely won't even have the full strength of a soldered joint. And third, his brake, and his life, depends on the strength of that joint!

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You can imagine the conversatins I had had with Lumiweld ( and the dozen or so other similar products ) vendors over the years .
It has its place , a substantially smaller one than the BS provided with it pretends to , but a high stress shock loading is not one of them
And yes I am yet to see some one do one properly ( including me ) on anything other than a sample billet or beer can.
Beer cans are a con because under the paint they are perfectly clean, so warm enough to burn the paint off and a reducing flame = no oxide barrier to overcome
And pretty sure it is technically not even solder as the joining metal has to be able to alloy with both of the parent metals so a mouldable hot melt glue would be a more truthful description

As for the journo, again very few have any formal technical qualifications in the fields they write about .
Their sole skill s assembling a string of words together that are readable and inviting.
I spent 30ish years at the beck & call of a lot of publishers & there are very few I would beliieve anything they printed was correct apart from their own name.


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Vibration

I have a vibration app on my iPhone that works with the camera's internal sensors, that has been quite useful for several motorcycle-related applications. There are several such apps in the Apple store, but the one I've had for at least ten years has worked fine for me, unimaginatively named 'Vibration'.

[Linked Image]

I used this app to distribute extra weight on my lathe to minimize the vibration at the headstock and, most recently, used it to balance the coupler for the 3-phase motor and VFD I installed on my mill.

The next composite shows that the coupler has four holes in it that should, and does, cause an imbalance.

[Linked Image]

The next composite shows the vibration for the above three configurations: the "raw" coupler, and with clamping screws of different lengths/weights filling those holes.

[Linked Image]

Thanks to this vibration app I was able to cut screws to lengths that resulted in imperceptible vibration of the motor even at its highest speed, which can only be a good thing when machining a valve seat.

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MM: I can only occasionally look in on this thread because every time I look I end up in my shop sulking while staring into my near empty "measurement tools" box.

I have two micrometers, two digital metal calipers, one non digital metal caliper, a few thread gauges, several sizes of machinist metal rulers. a digital angle gauge, two metal drill size gauges and several metal tape measures. That is about it, such embarrassment. Even throwing in a plastic slide rule (from 1960s physics classes) does not bring the total up to even one of your posts.

Gordo


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Originally Posted by Gordo in Comox
my near empty "measurement tools" box.
For years it's been an almost-daily source of amusement for my wife when I say "I'm going out to the garage to measure something," as if that's not a perfectly normal thing to do...

After touring my physics laboratory some years ago a Russian physicist remarked, with a Dr. Strangelove-like intonation, "With the equipment in your laboratory, there are no secrets Mother Nature can keep from you!" I used the same approach to assemble my motorcycle "laboratory."

Laser Alignment

The next photograph shows a laser that is very useful for checking frame alignment.

[Linked Image]

The laser sits on a "floating" platform, leveled by gravity, inside the body of the instrument that is mounted on a tripod. The unit can be set to output a vertical line, a horizontal line, or both. This laser was a huge help when I straightened the frame that I hope to (eventually) use on my bitza BSA "Alloy Clipper."

After much work to straighten the frame, aided by this laser, the next photograph shows the front downtube and engine mount are correctly aligned at 90° with respect to a steel rod sitting in the rear wheel mounts.

[Linked Image]

However, it can be seen that at the time the photograph was taken that the headstock was slightly tilted. A second laser that is accurately aligned with its housing, along with an adapter I made for it that fits in the headstock, is shown in the next photograph.

[Linked Image]

The upper part of the next composite shows that the two laser beams coincide on a white card held against the bottom of the headstock, and the lower part shows that using this laser allowed me to twist the headstock until the beam from it was within ~1 mm of that from the other laser at a distance where the front wheel would touch the ground.

[Linked Image]

I've never measured an unmolested NOS BSA frame, but I doubt any of them left the factory with alignment better than this.

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Jig welded in a non temperature controlled environment there is next to no chance of consistent results with that accuracy
It would be interesting to know if frames were eyeballed and "adjusted " before painting.
Although I have had frames straitened by te Alderton Bros who used eyes and long levers and by a workshop with a "Motolinner" computer contrlled hydraulic frame aligning machine,,,
Guess which frame repair rode straitest ?

OTOH you have created a spark .
Should be able to use the not particularly finely calibrated lazer measuring tool to check wheel alignment .
Need to have a little think about it .
Has to be better than the string I use at the moment as there is no longer enough clean floor space to drop centers with a plumbob & chalk out

Last edited by BSA_WM20; 01/13/22 11:05 am.

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Pressure

Although "pressure" and "vacuum" might seem to be different, both are terms for pressure, depending only whether it is lower or higher than atmospheric pressure (14.7 psi; 1 atm; 1.01 bar; 1.01 kPa; 760 mmHg; 27.92 in.Hg). Still, I'll treat them separately since that is what is commonly done.

Most pressure gauges we are concerned with measure 'gauge pressure', psig, rather than actual pressure, with psig being the pressure relative to atmospheric pressure. For example, if the gauge in the next photograph measured actual pressure the needle would be pointing at 14.7.

[Linked Image]

With its 60 psig maximum, the above pressure gauge would be useful for something like a paint gun, although a 30 psig gauge might be a better choice for that, whereas a 150 psig gauge would be a better choice for a blasting cabinet.

[Linked Image]

This common type of pressure gauge is based on a mechanism that use a 'Bourdon tube', so I can't help but note that the world's first motorcycle, the steam-powered Michaux-Perreaux that NYBSAGUY and I had at the Guggenheim and in Brisbane, used a pressure gauge that was manufactured by none other than Monsieur Eugène Bourdon himself.

[Linked Image]

Digital gauges that are accurate to 0.05% and that can display in a wide variety of units also are available.

[Linked Image]

However, for all but very few applications I prefer old fashioned analog gauges. I seldom need more resolution than they provide, and none of them as yet had a battery wear out.

A 60 psig tire pressure gauge handles most motorcycle uses, although a 15 psig tire gauge provides better resolution for use on a trials bike.

[Linked Image]

Note that although the three tire gauges at the left in the above photograph all are 60 psig, the ends that connect to the stems on the tubes differ. Different angles are needed depending on how much room the spokes allow (or, on a modern bike, if a disc is in the way). Also, I included an old-fashioned stick-type tire pressure gauge in the photograph because these are quite useful for carrying in a bike's toolkit. As for the accuracy of one of these stick gauges, it certainly is much higher than if one fills a tire without the benefit of any gauge at all.

Moving to somewhat lower pressures, the following gauge is limited to essentially 10 psi, but has resolution of 1 oz./square inch (0.062 psi).

[Linked Image]

If nothing else, showing that it isn't always easy to draw a distinction between gauges for pressures that are greater or less than atmospheric, a Relative Air Density gauge used for jetting carburetors measures the air pressure relative to standard atmospheric pressure, which is typically less than 100% for all but cold days at sea level.

[Linked Image]

Since in most situations this gauge will measure a value less than standard atmospheric pressure, I should have had it in the 'Vacuum' section if things could be categorized so simply. Which, clearly, they cannot since even at the top of a tall mountain we speak of the reduced atmospheric pressure, not vacuum.

Moving to higher pressures, a 5000 psig (2½ ton) gauge is used on the following device that was made for weighing the hitch on truck trailers.

[Linked Image]

Even though it only goes to 2½ T, I've used this device on my 30 T hydraulic press to measure the clamping force of several motorcycle-related parts, which seldom exceed the range of this unit. I also used it to determine the weight on both axles of my motorcycle trailer and on the hitch, to make sure the weight distribution was appropriate.

A compression tester is another use of a pressure gauge.

[Linked Image]

Ignoring heating of the air as it is compressed, an 11:1 compression piston would increase the pressure in the cylinder to 162 psi. However, heating increases that further, which is why a 300 psig pressure gauge is appropriate for a compression tester for gasoline engines.

The final example of the use of pressure gauges in the garage is a leak down tester.

[Linked Image]

The unit is connected to a spark plug hole via the connector at the right and high pressure is applied via the connector at the left. If there were no leakage past the rings or valves, both gauges would read the same pressure. However, any leakage results in a pressure drop across an orifice between the two gauges, causing the gauge at the right to have a lower reading that is proportional to the leakage rate.

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i use a RAD gauge for tuning carbs both when i change something and at the races to keep track of what is going on. ive got a thermometer too, but mostly the RAD gauge accounts for temperature. in cool mornings at loring's 800 feet ive seen as high as 104 percent for a little while. if you dont run computerized fuel injection RAD is important. i saw 108 once, iirc. that seems awful high so i need to look at my notes

my gauge is an analog longacre brand. they seem to have switched over to digital now

im curious about stuff so im looking for an interesting sling psychrometer. i dont anticipate ever being good enough to make use of humidity in tuning, but you never know.


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Originally Posted by kevin
im looking for an interesting sling psychrometer.
As the following graph shows, it will be especially important to have if you attempt to set a speed record on a hot day in Hawaii during the summer monsoon, where the effect of humidity on RAD could be as large as 5%.

[Linked Image]

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i would be delighted to give it a try, if i could get some beach time in too


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Originally Posted by Magnetoman
......The next photograph shows a laser that is very useful for checking frame alignment........
Yes yes, I remember that photo from the early days of Covid panic when I was busy with my own bent frame BSA project. I was planning to go the plumb bobs and string route but the $50.00 laser level was a no brainer. Thanks MM for that tidbit of extremely useful info. That bike has been up and running for a year or so now and will coast hands off!

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Vacuum

The next photograph shows a vacuum gauge with maximum reading of '30'.

[Linked Image]

A perfect vacuum would support a column of mercury that is 29.92 inches high, which gauges round off to 30, telling us this gauge reads in units of inches of Hg.

Although I have a vacuum pump and an air compressor, a device that I find quite useful is a combination vacuum/pressure pump operated by hand, although it is the vacuum mode that I almost always use it.

[Linked Image]

As can be seen, it has a dual-operating gauge that reads to 30 in.Hg for vacuum and 30 psig for pressure. Obviously, its pumping speed is quite limited, but it actually is more useful than a compressor or vacuum pump when checking the sealing of small volumes. The next photograph shows this pump being used to test the seal on the sight glass on my 1928 Ariel.

[Linked Image]

For small pressure drops, i.e. small vacuums, the following digital manometer reads to 1.999 psi (4.1 in.Hg) below atmospheric, with a resolution of 52 mTorr (a unit to be discussed shortly). It also reads increased pressures above atmospheric up to 1.999 psi.

[Linked Image]

The photograph shows this manometer connected to the oil pump of my Ariel to test it with the new piston I had made for it. In operation the oil pump has to create a sufficient vacuum to lift oil ~4" from the tank into the sight glass. Motor oil has a density ~90% that of water, so since a perfect vacuum would support a column of water 33.9 ft., it would support oil 37.7 ft. (452"). Consequently, the pump only needs to create drop in pressure with respect to atmospheric of ~4"/452"×30 in.Hg= 0.27 in.Hg (0.13 psig).

It's a 'manometer' because it uses two inlet ports and measures the relative vacuum/pressure difference between them, rather than having the single inlet port of common gauges that measure the vacuum/pressure difference between it and atmospheric (i.e. the gauge pressure). Of course, one inlet port of a manometer can be left open to the air, in which case it measures the gauge pressure/vacuum.

The next photograph shows this manometer being used with a flow bench for measurements on carburetors in different configurations.

[Linked Image]

Here, one port is connected to the fitting below the main jet of a Monobloc and the other end is open to air, to measure the relative pressure difference at a given air flow rate through the carburetor that would "push" fuel up into the throat of the carburetor.

Going lower in pressure, i.e. higher in vacuum, the unit 'inches of Hg' is no longer of convenient size so it's common to change to mm of Hg to gain a factor of ~25× in resolution. A perfect vacuum will support a column of mercury 760 mm high, and 1 mmHg is given the name Torr. From 1 Torr to 10–3 Torr it's common to express vacuum in milliTorr,

Mechanical vacuum gauges have reached their limit by 25 Torr (1 in.Hg), so electronic gauges are required for vacuums lower than that. The next photograph shows a meter that's used with a particular type of electronic pressure gauge that is sensitive in this range.

[Linked Image]

The gauge mated to this meter and control unit is based on the fact the thermal conductivity of air is proportional to vacuum in this range, and the gauge uses a hot filament and thermocouple as the sensor.

[Linked Image]

The operating range of a "thermocouple gauge" is well matched to the capabilities of mechanical vacuum pumps that are available for under $100 and that produce vacuums as low as ~1 mTorr.

One reason vacuum pumps and gauges are relevant for motorcycle work is that if you pot a magneto armature, or the exposed coils on an early type of stator, with something like epoxy or Glyptol, and want to make sure it flows to cover all the internal windings, this is accomplished by pumping the air from a chamber to "suck" the liquid into the windings.

Another application of vacuum is to check the sealing of the valves to the seats. A vacuum pump is used with a plate having a gasket and a fitting for the vacuum pump hose, along with a 0–30 in.Hg gauge. Tests can be done from the intake or the exhaust side, whichever is easier to have a plate seal against.

The level of vacuum and pumping speed of a small mechanical pump is quite sufficient for work like this, and for every other motorcycle-related purpose that I can think of.

Last edited by Magnetoman; 01/14/22 11:57 pm. Reason: mTorr=micron
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Hello Magnetoman,

Sincerely enjoy all the technical stuff you write! What a thread!! I can read it and brush up on stuff I used to know, stuff I never knew, and stuff that will become important at some point, maybe.

Hey, my brain was pretty full and then I read:

"The operating range of a "thermocouple gauge" is well matched to the capabilities of mechanical vacuum pumps that are available for under $100 and that produce vacuums as low as ~1 mTorr (nb. they may claim base pressures of ~100 microns = 0.1 mTorr, but in my experience a few mTorr is more realistic for this type of pump)."

I work in microns when I perform HVAC work and knew about the unit named after Torricelli, but could not reference it correctly and had to go look it up: 1 mTorr = 1 micron. So, "...~100 microns = 0.1 mTorr..." is incorrect.

Also, when you use the tilde (the ~) are you using it as an equivalent to the mathematical symbol for approximately equal to, or some other use? I was trying to come up with the micron to Torr equivalency in my head and thought the approximately equal may be the key to remembering, but thinking that and nothing happened and had to go look it up.

No rush responding. I have tilde call me to go make dinner.

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Right you are. I fixed that glitch. I posted that at 8:30am, before the coffee had kicked it, but there really isn't an excuse since the meter I posted clearly shows that it reads in "millitorr/microns." The origin of my decaffeinated mistake is that a Torr already has a "milli" build into it since it's is a millimeter of Hg, so a milliTorr is 10–3 of a mm of Hg, which is a micron of Hg. But, it's even worse than me not reading the meter, since I've used thermocouple gauges for half a century and used 'milliTorr' and 'micron' interchangeably countless times. Sigh...

Originally Posted by Bustednukel
Also, when you use the tilde (the ~) are you using it as an equivalent to the mathematical symbol for approximately equal to
Yes, I use it to mean approximately equal to. There are several ways to indicate an approximate equality, with slightly different meanings to each. In addition to the ~, the Alt-code cheat sheet hanging above my computer has ≈. Although there don't seem to be Alt-codes for them, there's also a two-line symbol that's a modified = but with ~ as the upper line, and a three-line symbol with ~ above the =.

Somewhat depending on the context, if I were writing something in the scientific literature I might use three of the symbols in the following way

π = 3.14159...
π ≈ 3.14
π ~ 3

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Originally Posted by Magnetoman
...... a device that I find quite useful is a combination vacuum/pressure pump operated by hand, although it is the vacuum mode that I almost always use it.
[Linked Image]
it....is....useful ... when checking the sealing of small volumes.......

Yes, very.
And here's a real world use for the type of guy that is on this forum:

Use it to vacuum check float needle and seat sealing. In the world of iffy quality we live in these days, it will quickly show if you've got a good one or not. When rebuilding SU's or Webers, I've gotten into the habit of checking every needle and seat this way before installing them. Might be a good idea on Amals too. Especially triples.

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And now they are changing to the mBarr (and - powers of ten Barr for lower pressures) for vacuum readings. I like the Torr. We regularly worked with 10^-8 Torr range and I did build one apparatus that reached 10^-12 Torr range (really exotic gauges and procedures for that).

And the use of relative terms in vacuum is always confusing - higher or lower vacuum. Using higher or lower pressure has no confusion. High vacuum region is permissible as it is a range, not a direction.


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Originally Posted by Stuart Kirk
Originally Posted by Magnetoman
...... a device that I find quite useful is a combination vacuum/pressure pump operated by hand, although it is the vacuum mode that I almost always use it.
[Linked Image]
it....is....useful ... when checking the sealing of small volumes.......

Yes, very.
And here's a real world use for the type of guy that is on this forum:

Use it to vacuum check float needle and seat sealing. In the world of iffy quality we live in these days, it will quickly show if you've got a good one or not. When rebuilding SU's or Webers, I've gotten into the habit of checking every needle and seat this way before installing them. Might be a good idea on Amals too. Especially triples.


FWIW,
SOP for small engines
Particularly blue smokes than need crankcase seals that hold both pressure & vacuum
As for carbs, the std test is to invert the carb so it is just the weight of graavity holding the needle closed
A good seat will hold 10 psi or better
A cube carb needs to hold 15 psi
A small engine fuel pump typically runs at 7psi


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Carburetor Air Flow

Strictly speaking, the instruments in this section should be in the 'Vacuum' section because they work on the reduced pressure due to air flowing through a venturi.

The bottom row of the next photograph shows two gauges that are held in turn over the face of each carburetor on a multiple-carburetor motorcycle, with adjustments made to the carburetors until the air flow readings from all the carburetors are the same at idle.

[Linked Image]

The top row is an angled adapter that can be used when frame tubes, oil tanks, or other obstructions are in the way.

The instrument in the next photograph also is used to balance multiple carburetors, but rather than using a venturi in the device itself it uses one in the inlet manifold.

[Linked Image]

While this instrument allows the flow through all the carburetors to be seen simultaneously by balls that "float" in the sight glasses, it requires fittings in the manifold to which the tubes can be attached. Later twin-cylinder bikes with balance tubes have the necessary ports, but most machines would have to be drilled and tapped to accept them.

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There used to be a fellow in Sacramento who made these instruments for balancing the carbs on twins, selling them through the AdvRider website:

[Linked Image]

It's a great little device, sensitive and with a build in tach. Could also be used as a single ended vacuum gauge.

Sadly, he passed away suddenly several years ago, and these are no longer available .


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Carb balancing vacuum gauges are great for ensuring the smooth running of any multi-cylinder bike and I regard them as an essential tool for anyone doing home tuning.

Over the years, I've tried a few varieties of carb balancers and have found the dial type to be the least sensitive and the mercury/steel rod/ball types most accurate.

The best one I've used is the Morgan Carbtune, which originally came with a small bottle of mercury that you had to self fill when it arrived. The mercury sat in vertical tubes with baffles on either side.

I still have my original Carbtune complete with mercury, which now, over the years appears to have filled with small air bubbles, so I'm doubtful of its current accuracy, not to mention its poisonous nature. The later Carbtunes have steel rods in place of the mercury for health and safety reasons.

Would be interesting to know if there are any tests that show how accurate the different type of vacuum gauges are for home use.


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Originally Posted by gunner
I still have my original Carbtune complete with mercury,
The issue with a mercury manometer isn't so much the toxicity of the vapor within the unit (although storing it next to a heater in an enclosed garage isn't a great idea), it's the risk of screwing up and having it being pulled into the engine and blown out the exhaust in a fine mist that ends up in all the cracks on the floor. If that happens, it will give off vapor "forever" from its now-huge surface area. The vacuum generated by the engine isn't enough to do this all by itself if the tubes remain vertical, but the risk is in tilting them while repositioning them when the engine is running.

I consider the risk of something untoward happening with the 50 lbs. of cadmium-containing Cerrobend® that Cyborg forced me to buy to be considerably less than what might happen with a few ounces of Hg in open tubes connected to a running engine.

Originally Posted by gunner
Would be interesting to know if there are any tests that show how accurate the different type of vacuum gauges are for home use.
A device that uses Hg would be a manometer that measures the pressure/vacuum relative to atmospheric. The reading of these depends only on the density of the liquid in the manometer. However, accuracy actually isn't important. What matters is all the tubes have the same reading for the same pressure. Checking that is easy to accomplish by connecting all the tubes together in one fitting, to which only one measuring tube goes to something that generates a small partial vacuum.[*] If all the Hg in all the tubes come to the same level, which they should, the device is fine.

[*]CAUTION!: a good vacuum will support a column of Hg that is 760 mm (30") high, and these carb synchronizers are far shorter than that. Consequently, if you apply even a fairly modest vacuum to them you risk sucking the Hg into your vacuum pump, from which it will be blown as a fine mist from the outlet.

In contrast, devices that use floating balls or cylinders of metal measure the air flow through them caused by the relative pressure/vacuum difference. The Suzuki synchronizer in my previous post is of this type. Like the Hg manometer, all the matters is that all tubes have the same reading for the same pressure drop. This also can be checked by tying them all together and connecting to a single vacuum source. In this case a too-large vacuum only pegs the balls against the top, rather than filling your garage with Hg.

Out of curiosity I connected one tube of that Suzuki balancer to the following bank of air flow gauges that are connected in series.

[Linked Image]

With the hand-operated vacuum pump shown in a recent post, I was able to momentarily get the ball just past the 10 scfh (standard cubic feet per hour) mark, and at the same time the ball in the balancer most of the way to the first mark. A 250 cc cylinder at a 600 rpm idle would fill itself 300 times/minute = 75,000 cc/min. = 4.5 Mcc/hr. = 160 scfh. This says air flow into the inlet manifold from the synchronizer would be ~6% of that through the carburetor. This wouldn't dilute the mixture by a too-significant amount so the engine would continue to idle smoothly. Smooth idle, rather than perfect mixture, is all that is needed for synchronizing the carburetors.

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