Importance of float level

Michael Forrest /

On small carbs the distance from the top of the gas in the float bowl to the carb throat is less than that of large carbs. So the percentage of error is greater if your float level (gas level) is off. On a 14mm carb I measured a 16mm distance. So if the float height was off by 2mm then that would be a 12% error. 2mm of 32mm of a large carb would only be a 6% error. This all matters because the suction in the carb throat is what pulls up the gasoline from the float bowl and the larger the distance, the less gas is pulled up, which would make it run leaner. And the smaller the distance, the more gas is pulled up.

carbfloat.gif

Re: Importance of float level

> Michael Forrest Wrote:

> -------------------------------------------------------

> On small carbs the distance from the top of the gas in the float bowl to

> the carb throat is less than that of large carbs. So the percentage of

> error is greater if your float level (gas level) is off. On a 14mm carb

> I measured a 16mm distance. So if the float height was off by 2mm then

> that would be a 12% error. 2mm of 32mm of a large carb would only be a

> 6% error. This all matters because the suction in the carb throat is

> what pulls up the gasoline from the float bowl and the larger the

> distance, the less gas is pulled up, which would make it run leaner. And

> the smaller the distance, the more gas is pulled up.

You do realize that a carb that's 16mm is the reference to carb opening and NOT float level.

Lots of floats are not even adjustable.(edited)

Re: Importance of float level

Michael Forrest /

Do the words "I measured" not have any significance?

Re: Importance of float level

> Michael Forrest Wrote:

> -------------------------------------------------------

>On a 14mm carb

> I measured a 16mm distance. So if the float height was off by 2mm......

^^Your statement implies that a 16mm carb should have a 16mm float height.

A 16mm carb will have a 16mm opening in throat not a 16mm float height.

So what other questions you got?(edited)

Re: Importance of float level

Michael Forrest /

yes the implication is that the larger the carb the longer the distance from the carb throat to the top of the fuel in the float bowl. But the example I gave was just for illustration purposes. Reality is often quite variable from our ideal illustrations. But the point remains that float level is important.

Re: Importance of float level

O.

Re: Importance of float level

Dude your a genius!

And its not suction in the carbs that pulls the fuel thrue. When the air coming thrue the carb passes over the top of the atomizer it causes a vacuum that pulls the fuel up.

It’s called bernoulli's principle

Re: Importance of float level

Michael Forrest /

Bernoulli's principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure. Yes but it is the vacuum created by the rising piston that creates a pressure drop which creates the air/fuel speed. And there is a suction wave traveling from the engine to the carb. All these add up to pull the fuel up from the float bowl.

(boy you people like to argue)

Re: Importance of float level

Do you know why raising the fuel level increases fuel flow?

Re: Importance of float level

Michael Forrest /

Obviously you think I don't so I'll just play dumb so you can enlighten us all

Re: Importance of float level

> Michael Forrest Wrote:

> -------------------------------------------------------

> Obviously you think I don't so I'll just play dumb so you can enlighten

> us all

All?

No one else around here is copying and pasting basic knowledge from the internet to these forums but you.

Re: Importance of float level

> Michael Forrest Wrote:

> -------------------------------------------------------

> states that an increase in the speed of a fluid

> occurs simultaneously with a decrease in pressure. Yes but it is the

> vacuum created by the rising piston that creates a pressure drop which

> creates the air/fuel speed. And there is a suction wave traveling from

> the engine to the carb. All these add up to pull the fuel up from the

> float bowl.

>

> (boy you people like to argue)

The engine vacuum does not pull the fuel thrue the carb directly. The engine vacuum causes air to Be pulled thrue the carb. when the air passes over the atomizer it cause a separate vacuum. The separate vacuum happing in the carb’s atomizer pulling the fuel thrue is called Bernoulli's principle(edited)

Re: Importance of float level

Michael Forrest /

Rocco,

1) there is a vacuum wave that travels along that path from the engine which pulls up fuel. It follows the same principle as when the exhaust port opens and a pressure wave is created which travels at the speed of sound. That wave is somewhat independent of the actual pocket of pressure which is the exhaust.

2) there is vacuum all along that path till the air filter

3) there is the Bernoulli effect on the jets

All three combine to pull up fuel through the jets but the farther the distance to the fuel, the less fuel is pulled up.

Re: Importance of float level

Michael Forrest /

Rocco the Rat - please show me the site from where iI copied this info.

Yes it is basic info but there are many people here who are rookies when it comes to 2 stroke engineering and need to hear the basics. Can I not do that without rats nibbling at my feet? Do I need the rats permission? Are not forums places to freely share ideas?

Re: Importance of float level

> Michael Forrest Wrote:

> -------------------------------------------------------

> All three combine to pull up fuel through the jets but the farther the

> distance to the fuel, the less fuel is pulled up.

Guess again. Vacuum does not decrease because of distance inside of a tube.

Re: Importance of float level

Michael Forrest /

boy between Evil and Rats (Rocco) a guy just can't get a break here.

yes the vacuum doesn't decrease because of the length of the tube but the weight of the fuel in the tube does increase. With more weight then more vacuum is needed to pull up the same amount of fuel. But with the same vacuum then less fuel is pulled up.

Re: Importance of float level

> Michael Forrest Wrote:

> -------------------------------------------------------

> Rocco the Rat - please show me the site from where iI copied this info.

>

> Yes it is basic info but there are many people here who are rookies when

> it comes to 2 stroke engineering and need to hear the basics. Can I not

> do that without rats nibbling at my feet? Do I need the rats permission?

> Are not forums places to freely share ideas?

Rocco didn't call you out I did!

There is a search function for rookies and some use it.

You seem to be one of the biggest rookies here M.F. and now a self proclaimed engineer too?

I love engineers. 99% classroom and book knowledge with 1% real world experience. Let me guess, you have an FA50 that goes 70mph too, right?

Ladies and gents I give you:

Michael forrests 2 stroke oil calculator

Re: Importance of float level

> Michael Forrest Wrote:

> -------------------------------------------------------

> boy between Evil and Rats (Rocco) a guy just can't get a break here.

>

> yes the vacuum doesn't decrease because of the length of the tube but

> the weight of the fuel in the tube does increase. With more weight then

> more vacuum is needed to pull up the same amount of fuel. But with the

> same vacuum then less fuel is pulled up.

Wrong genius,

You dont dive much do you?

Re: Importance of float level

Braedan Cvetkovich /

When is MA going to add a "hide topic" / block user function? Tired of seeing this doinks posts all the time.

Re: Importance of float level

well if we want to get technical, vacuum doesn't PULL anything... atmospheric pressure PUSHES the fuel out of the bowl through the bowl vent.

;)

Re: Importance of float level

> ken gilbert Wrote:

> -------------------------------------------------------

> well if we want to get technical, vacuum doesn't PULL anything...

> atmospheric pressure PUSHES the fuel out of the bowl through the bowl

> vent.

>

> ;)

Haha yea i have a difficult time understanding stuff like that. Gravity pulls it doesn’t push and the wall pushes back with the same amount of force.

I’m really wasn’t the best student

Re: Importance of float level

> ken gilbert Wrote:

> -------------------------------------------------------

> well if we want to get technical, vacuum doesn't PULL anything...

> atmospheric pressure PUSHES the fuel out of the bowl through the bowl

> vent.

>

> ;)

Correct!!! ^^

And the deeper a body of liquid is the higher the pressure becomes at the bottom.

Its that added pressure that aids in more fuel delivery not the travel distance being reduced. Distance to the venturi has nothing to do with it Michael.(edited)

Re: Importance of float level

Michael Forrest /

To prove that the suction pulling the gas up is due in only a very small amount to the Bernoulli effect, I want you to consider that effect only happens when there is a change in flow area so that under the front of the slide, when it is fully or partially closed, the area is smaller and so the flow is faster than before it and after it and so the Bernoulli effect creates vacuum there which acts mostly on the idle jet which is under the front of the slide. The needle and main jet are before this contracted area but still are at a slightly contracted area being under the middle of the slide. So the Bernoulli effect acts mostly on the idle jet and a little on the needle/main jets. Like I said before, there is some vacuum all the way between the engine and the air filter which acts on the jets, pulling up fuel from the float bowl which is at normal air pressure since the bowl is connected to outside air pressure via a breathing tube.

There is also a vacuum wave which some carbs make extra use of by the raised half shrouds extending up from the needle jet. They catch more of that wave and so the higher the shroud, the smaller the jets need to be.

Re: Importance of float level

Michael, are you using a language translator?

Re: Importance of float level

> Michael Forrest Wrote:

> -------------------------------------------------------

> To prove that the suction pulling the gas up is due in only a very small

> amount to the Bernoulli effect , I want you to consider that effect only

> happens when there is a change in flow area so that under the front of

> the slide, when it is fully or partially closed, the area is smaller and

> so the flow is faster than before it and after it and so the Bernoulli

> effect creates vacuum there which acts mostly on the idle jet which is

> under the front of the slide. The needle and main jet are before this

> contracted area but still are at a slightly contracted area being under

> the middle of the slide. So the Bernoulli effect acts mostly on the idle

> jet and a little on the needle/main jets. Like I said before, there is

> some vacuum all the way between the engine and the air filter which acts

> on the jets, pulling up fuel from the float bowl which is at normal air

> pressure since the bowl is connected to outside air pressure via a

> breathing tube.

>

> There is also a vacuum wave which some carbs make extra use of by the

> raised half shrouds extending up from the needle jet. They catch more of

> that wave and so the higher the shroud, the smaller the jets need to be.

The Bernoulli effect is everything! Without the Bernoulli effect a carb engine wouldn’t be able to consume it’s needed fuel. It’s the Bernoulli effect that makes it possible for the engine to “pull new fuel in”. Without each other they are nothing. The engine doesn’t “pull” fuel up thrue the float bowl, it “pulls” fresh air in thrue the carb, when this happens it cause a Bernoulli effect across the top of the atomizers, that effect then cause fuel to be “pulled thrue” the atomizer from the float bowl. The smaller the opening (smaller carb) cause the Bernoulli effect to be “stronger”. Try blowing across a top of a straw in some water with your mouth wide open vs just barly (like your whistling).

I know I probably used the worst choice of words. Sorry I’m surprised dirt Dillion didnt show up to call my dumb ass out

I love you ma sometimes! Your like a puppy that i haven’t decided To liked yet(edited)

Re: Importance of float level

meh carb atomizer is like 3mm off the deck. my carb is mad angled and it runs good

Re: Importance of float level

Michael Forrest /

Rocco, check out what the carburetor page of Wikipedia has to say;

"Bernoulli's principle, which is a function of the velocity of the fluid, is the dominant effect for large openings and large flow rates, but since fluid flow at small scales and low speeds (low Reynolds number) is dominated by viscosity, Bernoulli's principle is ineffective at idle or slow speeds and also in the very small carburetors of the smallest model engines. Small model engines have flow restrictions ahead of the jets to reduce the pressure enough to suck the fuel into the air flow. Similarly the idle and slow running jets of large carburetors are placed after the throttle valve where the pressure is reduced partly by viscous drag, rather than by Bernoulli's principle."

Re: Importance of float level

> Michael Forrest Wrote:

> -------------------------------------------------------

> Rocco, check out what the carburetor page of Wikipedia has to say;

>

> "Bernoulli's principle, which is a function of the velocity of the

> fluid, is the dominant effect for large openings and large flow rates,

> but since fluid flow at small scales and low speeds (low Reynolds

> number) is dominated by viscosity, Bernoulli's principle is ineffective

> at idle or slow speeds and also in the very small carburetors of the

> smallest model engines. Small model engines have flow restrictions ahead

> of the jets to reduce the pressure enough to suck the fuel into the air

> flow. Similarly the idle and slow running jets of large carburetors are

> placed after the throttle valve where the pressure is reduced partly by

> viscous drag, rather than by Bernoulli's principle."

Wait a minute you told me this last time.

“So the Bernoulli effect acts mostly on the idle jet and a little on the needle/main jets”

Re: Importance of float level

> Rocco Taco Wrote:

> -------------------------------------------------------

> > Michael Forrest Wrote:

>

> > -------------------------------------------------------

>

> > Rocco, check out what the carburetor page of Wikipedia has to say;

>

> >

>

> > "Bernoulli's principle, which is a function of the velocity of the

>

> > fluid, is the dominant effect for large openings and large flow rates,

>

> > but since fluid flow at small scales and low speeds (low Reynolds

>

> > number) is dominated by viscosity, Bernoulli's principle is

> ineffective

>

> > at idle or slow speeds and also in the very small carburetors of the

>

> > smallest model engines. Small model engines have flow restrictions

> ahead

>

> > of the jets to reduce the pressure enough to suck the fuel into the

> air

>

> > flow. Similarly the idle and slow running jets of large carburetors

> are

>

> > placed after the throttle valve where the pressure is reduced partly

> by

>

> > viscous drag, rather than by Bernoulli's principle."

>

> Wait a minute you told me this last time.

>

> “So the Bernoulli effect acts mostly on the idle jet and a little on the

> needle/main jets”

Wikipedia? Dude try mopedarmy!(edited)

Re: Importance of float level

hmm, i'm not exactly sure that i'm doing the math correctly but i'm pretty sure the original assertion here is wrong.

the pressure differential that you are overcoming with suction at the emulsion tube or jet is going to be based on the mass of the fluid at a given height, like a water column.

so, gas being sucked up say 2 cm in a large carb vs. being sucked up 1 cm in a small carb is going need 2 cm or 1 cm 'water column' which in this case is gasoline.

it doesn't matter if the float bowl is overall 5 cm deep or 3 cm deep (for the respective examples) if the float height causes the fuel level to be at 2.2 cm vs 2 cm it will be off by the same amount of pressure as the float height being 1.2 cm vs 1cm, the pressure differential will be equal to .2 cm x the specific gravity of fuel in either case.

now, how sensitive to the precise 'fluid column' pressure the carb is relative to the venturii and other dimensions, i think generalizing that is going to be tough. I have noticed big differences between different carbs regarding how sensitive they are to float height. I recently was tuning a VM28 on a big air cooled 2 stroke and that thing was ultra picky, where as something like a 14 SHA doesn't seem to care at all. I'm sure it has a lot to do with the strength of the vacuum signal relative to the sizing of the jets. If you have a big carb with low vacuum signal and large jets the fuel pressure differential across the jet is low and the relative impact of the fluid column pressure is high in altering the mass flow rate through the jet. If you have a small carb with a strong vacuum signal like a SHA (which also has some wacky emulsion tube tech) and a small jet with high pressure differential, the fluid column pressure will have a relatively small effect.

also,

don't talk shit on engineers, pretty much the entire modern world functions because engineers figured that shit out. this dude isn't any more an engineer than dr. phil is a doctor.(edited)

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