I've tuned my motorcycle's twin carburetors very successfully with a diy aquarium tube manometer the likes of what can be found plentifully on youtube.
The only addition I made was a needle valve at the bottom of the manometer to damp the fluid (red atf) till the point where things are almost dialed in. At that point the valve can be opened more in order to increase the sensitivity. Starting the tuning without the needle valve in place runs the risk of sucking atf into the carbs.

But I've been trying to imagine a dash mounted version of the manometer. The ability to tune the carbs "on the fly" under variable rpm and load conditions would be really great. There is this...

...a dual port analog center weighted needle. It's been used successfully for just this thing. But it's a rare bird, three inches in diameter, and how it would tolerate moving and vibrating conditions on a motorcycle is unknown. And it's rare. That is to say there are very very few, if any, similarly functioning and smaller gauges to be found.

So what about an electronic one?


This is the engine.
650cc opposed twin. Air cooled.

This is a very small 30 segment bar graph led that would fit into the "dash" of the bike

...connected to a dual port smd vacuum sensor

...which is ported to the carburetors vacuum ports. Range of about 10psi vacuum from center. Ideally two adjacent led segments (indicator) would be lit and centered when vacuum is balanced between carburetors. This indicator would need to be damped somewhat against pulsations. Drifting leftward/rightward indicating vacuum imbalance between the carbs.

I have no programming skills. Does this make my dream a non-starter?

Any ideas welcome! Any hacks that come to mind? A lot of the basics are already in a 5 dollar digital tire pressure gauge, assuming that a piezo pressure sensor can register vacuum as well as pressure. Or any other off the shelf shortcuts? Maybe something like this already exists? But a few days of search have turned up nothing close.

There are similar applications out there. Room pressure manometers for spray booths and electronic "clean rooms" utilize this basic gauge type to maintain balance or slight positive relative pressure. But they are generally analog/mechanical gauges not appropriate to my needs.

 

On the dual port gauge shown, what are the units shown on the face? ... Can't quite make out the print.

 

So what about an electronic one?

I don't see why not even for the electronically challenged. I would start with a differential pressure transducer similar to what you posted using two ports and looking at vacuum difference between each carburetor. I will confess I haven't a clue what the normal vacuum on that bike is but you choose a sensor with the right range. Then I would pipe the sensor out into a small micro controller like an Arduino and if you want to get really cool a simple cheap display. Whiting the actual code for the micro controller is pretty much a copy and paste of existing code samples. Honeywell markets a line or two of sensors which are inexpensive, like these for example. Arduino is just a common line of micro-controllers readily available at reasonable cost. Here is an example of using a pressure sensor with an Arduino. There are dozens of examples out there. Again, having never done it I really don't know the best sensor and range of the sensor but doing it is pretty plausible using modular building blocks.

Nice bike and ride safe. I currently ride a 92 (26 year old) Harley Electroglide. Next year I will be looking to add a smaller lighter bike similar to your 650 for cruising around locally.

Ron

 

I edited the original post to include a few more numbers. Range, etc.

 

10 psi sounds like over range for some of the common silicon sensors like the 26PC01SMT. Could you get by with something like +/- 25 inches of water, equal to 1 psi?

 

For fun, check out www.picaxe.com. It might be something you can understand.

The display might be harder. The Arduino offers a lot more power and floating point calculations.

There may be a need for averaging and/or peak-hold type of operations.

Driving LEDS, auto-dimming might be in the cards too.

 

Thanks for the replies. What might appear to be obsessive compulsion is really not. An opposed twin is capable of running as smooth as glass. Especially so for this very short stroke large bore 650. But very minor imbalances in ignition, valve clearances, and fuel supply manifest largely.

 

https://www.rammeter.com/texmate-am-30-led-bargraph-meter-50mv-100mv-200mv-1v-5v-10v-4-20ma.php

You could do this analog also, but either way, there are dragons to slay.
The gauge is only as good as it's zero setting, if you do it with micro, it could auto-zero every time the power comes up.

Auto zero is much harder with analog, a dumb little zero pot is the way to go.

 

A manifold absolute pressure sensor (MAP sensor) measures manifold vacuum. The 3 terminals are +5 volts, ground and a variable voltage output. I think the resolution is good enough for your project. You can get them cheap from G.M. cars at a salvage yard. one screw holds them on. Then read the analog voltage with an Arduino as was mentioned earlier.
MAP sensor - Wikipedia
https://en.wikipedia.org/wiki/MAP_sensor

 

-10PSI is in metric 690mB absolute vacuum 1000mB
The NXP is able to do what you want and make your live simple; output in voltage easy to handle.

https://www.nxp.com/docs/en/data-sheet/MPXV7025.pdf

Picbuster

 

I've tuned my motorcycle's twin carburetors very successfully with a diy aquarium tube manometer the likes of what can be found plentifully on youtube.
The only addition I made was a needle valve at the bottom of the manometer to damp the fluid (red atf) till the point where things are almost dialed in. At that point the valve can be opened more in order to increase the sensitivity. Starting the tuning without the needle valve in place runs the risk of sucking atf into the carbs.

But I've been trying to imagine a dash mounted version of the manometer. The ability to tune the carbs "on the fly" under variable rpm and load conditions would be really great. There is this...

...a dual port analog center weighted needle. It's been used successfully for just this thing. But it's a rare bird, three inches in diameter, and how it would tolerate moving and vibrating conditions on a motorcycle is unknown. And it's rare. That is to say there are very very few, if any, similarly functioning and smaller gauges to be found.

So what about an electronic one?


This is the engine.
650cc opposed twin. Air cooled.

This is a very small 30 segment bar graph led that would fit into the "dash" of the bike

...connected to a dual port smd vacuum sensor

...which is ported to the carburetors vacuum ports. Range of about 10psi vacuum from center. Ideally two adjacent led segments (indicator) would be lit and centered when vacuum is balanced between carburetors. This indicator would need to be damped somewhat against pulsations. Drifting leftward/rightward indicating vacuum imbalance between the carbs.

I have no programming skills. Does this make my dream a non-starter?

Any ideas welcome! Any hacks that come to mind? A lot of the basics are already in a 5 dollar digital tire pressure gauge, assuming that a piezo pressure sensor can register vacuum as well as pressure. Or any other off the shelf shortcuts? Maybe something like this already exists? But a few days of search have turned up nothing close.

There are similar applications out there. Room pressure manometers for spray booths and electronic "clean rooms" utilize this basic gauge type to maintain balance or slight positive relative pressure. But they are generally analog/mechanical gauges not appropriate to my needs.

I used to tune my TR3 with twin SU carbs using a piece of garden hose, one end to the ear and the other in the throat of the carb. When the pitch is the same they are balanced.

 

There are MAP and various dashboard monitors/meters at this site.
http://www.daytona-sensors.com/wego--general-tech-notes-and-tips.html
Is this something I might look into for a nearly off the shelf solution? I have yet to contact them but they may have something close enough to
"tweak" to my needs. That larger image below would be absolutely perfect if the needle could be simply centered at 50% indicating vacuum balance.

 

WEGO makes and markets good stuff in my experience with friends using their stuff. Yes, if they have what you want it would be a good, simple off the shelf turn key solution. I would contact them and provide all of the particulars of your bike to make sure what comes in the box is exactly what you want.

Ron

 

Anyone familiar with fluid mechanics?
The gauge above ranges from 0 to 10 "inches of water"
The rated pressure max is 15 psig.
According to a few sources online 15 psig is equal to 415 inches of water.
What am I misunderstanding here?

I'm told that 0-15 psig is adequate for my purposes with this project.
0-10 should be just fine since the grossed errors will simply bury the needle one way or the other.

Is there a simple mechanical/analog means of protecting the gauge from spikes in vacuum? Would an inline fixed setting 15psi 1/4npt brass bodied regulator (easy to find online), installed in reverse, do this?

 

Atmospheric pressure is around 15 PSI.

Since the engine "sucks" - creates a negative pressure, the max differential pressure would be 15 PSI.
That would be with one intake totally blocked, the other wide open.
But that might be pretty insensitive if you are looking for small DIFFERENTIAL pressures between carbs.

Try to find out what the actual vacuum pressure level is supposed to be, at the very least, get a unit that can withstand 15 PSI without damage.
Any type of pressure regulator in-line would horribly corrupt the readings.
in terms of spikes, just a long run of small diameter tubing coiled up would make a great spike attenuator.

 

27.7076 inches of water is equal to 1.0 PSI. The Magnehelic gauge above goes from -10 to 10 inches of water with a 0 center. Ten inches of water is right about 0.360912 PSI. The gauge zero is referenced to atmosphere.

According to a few sources online 15 psig is equal to 415 inches of water.
What am I misunderstanding here?

Yes, and what they are telling you is the Maximum pressure that can be applied (not measured) is 15 PSIG (Pounds Per Sq. Inch Gauge) before we actually damage the gauge. At that pressure the gauge needle will be pegged but the gauge guts will be OK until we exceed that limit.

Ron

 

Typically using a Uni-Syn to balance carbs is done outside of the carb as the air goes into it. It is not manifold vacuum. Is balancing manifold vacuum an alternate way of doing it? Valves, mixture and spark plugs can change manifold vacuum. So can ignition timing, but not relevant here.

If your sample tubes are in front of the carburetors, they won't be subject to extremes like manifold vacuum.

 

The balancing of multiple carbs is usually done to make sure the throttle butterflies are in time. so one carb isn't at idle and the other in it's transition area. Can't for the life of me see any advantage of doing it while the vehicle is moving/driving. Or at least I've never read or heard of anyone getting an advantage to performance by doing it.

 

I used to tune my TR3 with twin SU carbs using a piece of garden hose, one end to the ear and the other in the throat of the carb. When the pitch is the same they are balanced.

There is a project for you.
Use microphones inside tubes, (to reduce outside noise) with amplifiers. Then you can compare frequencies or use frequency to voltage converters and compare voltages.