Any engineers here? I have a flow rate question....

[Big Rich]

I'm sure somebody here will have an answer for this....

I want to measure the flow rate thru a passageway in a carb. There's no way for me to physically measure the diameter of the hole, so I'm hoping I can just rig up a fuel bladder above the carb with a hose going to the circuit, and measuring how much fluid comes out in a given amount of time.

If this is repeatable, and I'm able to duplicate the results with a known size jet in a hose, then I should have an equal flow rate for each..... right?

Maybe I'm over thinking this, but I'd rather not spend time guessing if I don't have to. Thanks in advance folks!

[lucas]

I don't know how to do what you're describing, but are you trying to determine your air/fuel mixture?  Cause you could install an oxygen sensor and hook up a digital gauge to it

[Big Rich]

Nope, not the A/F mixture.

Stock GR650 carbs have an "air induction system" that linked them to the cylinder head. I ditched the stock carbs for aftermarket Mikuni 34's, and want to try and use that induction system.

Here's a pic from the service manual (if it links properly.....):

https://www.google.com/search?q=gr650+air+induction+site:www.thegsresources.com&hl=en-US&biw=360&bih=530&prmd=sivn&source=lnms&tbm=isch&sa=X&ved=0ahUKEwid5923u6XMAhWGVD4KHZn8AQIQ_AUIBSgC#imgrc=-N2ttj7u8XCb9M%3A

Thanks though Lucas! I had an idea you'd pop in on this..... I appreciate it!

[Iarn]

Hey, something my trade may actually be useful for in the real world! I can't really envision the situation in which you're working, as I couldn't really figure that link out to the carb in question besides a simple picture of it working with the engine, so I'm going to say a lot of shaZam!, hoping I'm not preaching to the choir . Maybe you can rig something up with this stuff.


Let's see... volumetric flow rate is the volume of fluid that passes a given point over some period of time. The velocity of the fluid and the cross-sectional area of the pipe, or other container through which the fluid passes are the factors in volumetric flow rate. Multiplying these two factors provides a volumetric flow rate. You can use this formula for volumetric flow rate:

Q = A x V

Where:
Q = volumetric flow rate
A = cross-sectional area of the pipe/passageway
V = average fluid velocity over the pipe/passageway

If you know any of these two factors and a little bit of algebra, you can alter the equation to work for you.

You'll probably have an easier time trying to figure this out using the relationship between differential pressure and flow.

Fluid flowing in a pipe exerts pressure in two different directions. Pressure is exerted both in the direction of flow and against the walls of the pipe. These pressure measurements can be used to determine flow rate. If a restriction is placed in the pipe, effectively making the pipe smaller, the velocity of the fluid increases in the restricted area. As the velocity of flow increases, the pressure that the fluid exerts on the walls of the pipe actually decreases. The differences in the pressure before and after the restricted area can be used to determine the flow rate through the pipe. This pressure difference is called differential pressure. (DP)

The mathematical relationship between DP and flow is shown by the formula: Flow = √measured DP x maximum flow. (√=Square root)
                                                                                                                 √maximum DP

As the formula shows, the flow equals the square root of the measured DP divided by the square root of the maximum DP, multiplied by the maximum volumetric flow. The formula assess the flow this way: if the maximum differential pressure when the maximum amount of flow occurs is known, then the amount of flow at all other differential pressures can be calculated based on that change.

I'm not sure what sort of access you have, but my suggestion would to use a pitot tube as it's the simplest method to measure fluid flow velocity. A pitot tube can be used in conjunction with manometers and differential pressure gauges to determine the DP of fluids flowing in a pipe or duct. So you can theoretically use it to determine all the criteria you need to find your flow rate.

The simplest pitot tube is a tube that has a small opening, at the measuring end. This "impact opening" is positioned so that it faces directly into the path of the flowing liquid. The pitot tube impact opening and related tube tap provide the higher-pressure measurement point needed to determine a differential pressure. The lower pressure input needed to determine a differential pressure is typically obtained via a pressure tap located in the wall of the pipe or duct. Though I'm sure you could rig one of these up on your own.

If you can't manage to get a pitot tube working, I'll try to suggest another method.

Anyway, I have no idea if this was helpful or you can use any of this, but I'll just leave it here. Good luck!

[Big Rich]

Crap Iarn..... I don't know what you do for a living, but I hope you're payed well for it. Haha....

Thanks for the info buddy, but it's gonna take a while to digest all that.

[lucas]

Modern injected engines use Mass Airflow Sensors in the intake air stream... maybe that is something that you can use?

[Big Rich]

Welp..... never mind fellas. It occurred to me that Suzuki was mixing gas and air in the induction system. So even if I figure out the flow rate of the stock induction system, I can't duplicate it with my current carbs since I would only be adding air (can't fit a circuit between the carb and engine).

I genuinely do appreciate the input though.