Carburetor Float Bowl Volume

[oseaghdha]

Makes more sense to set the height of the fuel, rather than the amount.
I would suppose different floats could have different displacements.

Although it may not be much. Fly$hit in pepper, probably.

That's why I like my Holley (on my car, duh!) with externally adjustable floats. Makes it easy. You pop out the side plug and turn the screw until gas just starts to run out. I wish the Mikuni had an external adjustment.

[Lettuceman]

My technique so far has been to bench test the volumes. I fill from the removed fuel tank set on a crate above the carburetor, connect the fuel hose, open my manual petcock and fill. Once full I then remove the fill hose from the carburetor tee to ensure that no measurement of the fill hose volume is taken.

I then hold each bowl over a 500ml-measuring beaker and drain the bowl into the beaker. So far I have tried 60ml on one set and 65ml on a second set of 1979 carbs. I have not noticed any differences yet. Both these volume measurements seem to be within the 25.7mm +/- 1mm operating range.

I would love to hear other volume measurements to compare against.

[fabricgator]

I think the thing to shoot for is the fuel height as regulated by the floats as opposed to volume.

Lets say for some reason we put four gaskets.... about a 1/4" on a single carb.... just for arguments sake. The float is still going to regulate the height of the fuel level although there is going to be more volume in that bowl with the four gaskets. It is the relationship of the fuel level in proportion to the proximity of the various pick up points (jet, etc.)....

I agree that different floats and needle valves may regulate the fuel height differently no matter how accurately we strive to adjust them. I am going to verify the fuel height in the bowls (and leak check/valve operation) after my rebuild. Lets say for example we had a mis matched set of floats (3 brass and 1 rubber) it would be the same fuel level I would want to shoot for.

The four gasket proposal is just an example for this line of thinking regarding volume vs height.
Picking the pepper out of the fly $hite....

[Larrym]

Variables/Factors, Ranges and Repeatability

My technique so far has been to bench test the volumes. I fill from the removed fuel tank set on a crate above the carburetor, connect the fuel hose, open my manual petcock and fill. Once full I then remove the fill hose from the carburetor tee to ensure that no measurement of the fill hose volume is taken.

I then hold each bowl over a 500ml-measuring beaker and drain the bowl into the beaker. So far I have tried 60ml on one set and 65ml on a second set of 1979 carbs. I have not noticed any differences yet. Both these volume measurements seem to be within the 25.7mm +/- 1mm operating range.

Lettuceman,

I would love to hear other volume measurements to compare against.

I've got no Volume measurements to give you but I do hold a high regard for your investigative "need to know" approach. I mean what's really going on inside a carb/float bowl is something that so far we have to use indirect means to see/know. (Unless they make a bowl with a see through plate on the side...wouldn't that be nice?!)

You have seen/read the prior efforts made here on the site, right?:

http://www.xs11.com/xs11-info/tech-t...balancing.html

I thought it was an interesting read.

In particular I agreed with the conclusion:

Conclusion:
The irony of the situation with setting the float height on carburetors to me has always been that the goal is to set the fuel height inside the float bowl during operation consistently at a specfic height yet the actual configuration and measurement is made without fuel in the bowl with the carbs upside down!

While I agree that measuring the volume of the fuel in the individual float bowls is a valid indicator of what's going on inside and better than having no indicators at all, I see a few limitations in this method.

First, the scale you are using to measure the volume is too coarse. Because of the surface area at the top of the fuel level inside the bowls, a small change in fuel level (from 2-4 mm) needs a specific volume of fuel to make this change in displacement. I'm not gonna guess just how much this volume is but it is likely that a graduated cylinder with a finer resolution/scale would give more accurate/meaningful readings per carb/bowl.

Second, there are variations between the different float weights even though they may appear as the same with the naked eye. Sure, they are made to fit a specific geometry to fit inside the bowl and work with the pins/ needle but I believe that if you weighed each float on a triple beam balance scale you would find differences in weight. This weight variable along with minor volume differences in each float's shape would change the amount of fuel displaced by each float to achieve the same mechanical angle necessary for fuel shut-off. Each float would also displace a different amount of fuel and directly affect the fuel level/volume even if it weren't part of the metering system.

I'm onboard with the notion that the intended goal of making adjustments to floats is to achieve a fuel level within a specific use-able range. That's a very important factor for proper operation of the carbs. I believe that with the methods and measuring tools you have that only a seriously out-of-spec fuel level can be detected.

But keep on looking at things with a critical eye and trying to get as close to knowing everything that can be known.

[Yahman]

It's more about fuel height in the float bowl in relation to all of the little things that are sticking down into that fuel.

Have you ever taken a hose and tried to breath under water with one end held above the surface?

It's easy to breath when you're just under the surface, but it gets much more difficult as you go deeper. It's the same with those fuel circuits in the carbs, their designed to work properly with the fuel in a narrow range of depth. The amount or volume of the fuel isn't really important and has almost no affect on the function of the carb. You want to keep the volume so that there's enough fuel to supply the carb. You don't want too much fuel, to keep it from slopping around in the bowl. This keeps the fuel level as consistent as possible and keeps the depth within that narrow range.

Larry

[XS1100 Newbie]

Larry:
Why don't you figure out a way to make the floats externally adjustable for us. HE HE HE

[Yahman]

Larry:
Why don't you figure out a way to make the floats externally adjustable for us. HE HE HE

Sure! I'll get started on that right away.

Larry

[CatatonicBug]

(Unless they make a bowl with a see through plate on the side...wouldn't that be nice?!)

Like this one:

[Yahman]

That solves half the problem, now if I could just figure out an external adjust for the valve seat.

Right after I build that mouse trap I've been working on.

Larry

[fabricgator]

How about electronic fuel calibration.... you could adjust it by a serial port to your laptop.

[psycoreefer]

How about electronic fuel calibration.... you could adjust it by a serial port to your laptop.

Its been done! I'd like to do it but only because I think it would be a fun project. A little on the expensive side.

[cywelchjr]

How about electronic fuel calibration.... you could adjust it by a serial port to your laptop.

That's a cool mod. It's one I want to do some day, but it's gonna take a while to get the cash together for the parts. A couple of folks on here have done this and report better gas mileage along with the other benefits that come with the mod.

[Larrym]

Alternate Materials

Like this one:

Hah!!! Good one C-Bug!

Nice concept but the execution may lead to problems:

There once was a man named Mike
Who once built a plastic bike.
With plastic Pistons and plastic Crank,
With plastic Carbs and a plastic Tank,
With plastic Tires that were plastic Belted,

When he started it up the Darn thing MELTED.

[CatatonicBug]

When he started it up the Darn thing MELTED.

Well, the example was for a scooter, but the float bowls don't get hot, so I don't imagine it would be an issue as long as that was all that was made outta plastic. There are plenty of other plastic parts in there that work just fine too though.