Brett, there used to be a nice drawing with a good description on the net but the link doesnt work anymore,
heres what ive found.
http://www.duderacing.net/flow.html
https://www.intlwaters.com/gallery/thumbnails.php?album=62
here is some info regarding the build of a blood presure type meter, basicaly the same, just use a BP meter instead of a Mag meter.
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Ok I'm back... I will try this again.
To build a Flow meter using a blood pressure gauge you will need.
(1) A blood pressure gauge (sphygomanometer).
(2) 0 to 5 psi pressure gauge.
(3) A good quality pressure regulator. (An air compressor regulotor works good.)
(4) A small needle valve and "T" valve. (The best is to find a brass needle valve for fish tanks. This will have a needle valve and "T" all in one.)
(5) A small propane tank and valve assembly.
To build the meter you have to connect the propane tank to the pressure regulator. Most regulators have one input and three outputs. On one of the outputs connect the 0 to 5 psi gauge. On one of the other outputs connect the needle valve and add a "T" after it. Connect the sphygomanometer to one side of the "T", and add a long piece of tubing to the other side. This is the tube that you connect to your carb.
To use the flow meter. Connect the meter to a engine and make sure the engines needle valve is OPEN. The flow meters needle valve should be CLOSED at this time. Open the propane tank and adjust the regulator to 3 psi. The regulator needs to be adjusted to the same psi everytime you use it to be acurate. 3 psi seems to work the best, but you can use what ever you want, just as long as you use the same number each time.
The needle valve on the flow meter is to adjust the range of the sphygomanometer. At this time you can slowly open the valve and watch the sphygomanometer needle rise. Play around with your engines needle valve and the flowmeters valve to find a good spot to set the gauge at. You want it to have a full range of motion as you adjust your carb to the ideal setting. Because of this, all sphygomanometer flow meters are not the same! You have to set the flow meters needle valve and never touch it again or your gauge won't reflect readings taken it the past. Make sure to mount the needle valve inside the unit and think about ways to prevent it from moving.
Now your done!!! Take out your boat(s) and play around them untill you have the needle valve dialed in to the best performance. Then hook up the flow meter and record the sphygomanometers reading. Now you can find that "sweet spot" in the future just by hooking up the flow meter and adjusting the engines needle valve. Never count the number of turns out again or spent half the day trying to dial the boat in!
I like to hook up the flow meter to the engine with the fuel filter in line with it. This way the flow meter will take account for a dirty filter too! You can even use it to test the Flow of your cooling system. This way you can "see" the difference when you change the size of fittings, length of water lines, etc.
*** Just make sure you don't over extend the sphygomanometer gauge! ***
Don't turn on the flow meter with out the engines needle valve in the OPEN position.
Don't put your finger over the end of the tube that goes to the carb.
And Don't lend it out to friends to use with our your help!
Hope that helps! It took me along time to get this info my self. Seems like nobody wants to share this info. Please ask if you have any questions, and good luck!
Dale P.
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This should get you started atleast.
~James
