Re: Importance of float level

EX:

just after posting i remembered a really good example of this. Due to manifold constraints and packaging i went from a VM22 on a moped build to a VM18. Despite being similar design and layout, these two carbs are (obviously) different castings and always end up running really different tuning parts.

I had a 165 jet in the VM22, when i put the VM18 i was running a 75 jet. since mikuni jets are sized based on fuel flow, its easy math to see that dropping the jet size resulted in a (1-(75/165))= 65% decrease in flow rate through the jet.

now, the speed of the moped didn't decrease much, and it was properly tuned in both scenarios, which means we can assume that mass air flow rate stayed relatively constant and fuel flow rate stayed relatively constant.

so, because mikuni did the hard work for us and linearized the mass fuel flow rate of the jets, the math is really easy to say that (give or take) there was a 65% increase in differential pressure across the main jet to accomplish the same mass fuel flow rate with a smaller jet.

so the differential pressure of having a different float level setting as a percentage change in mass fuel flow rate decreased by a factor of whatever that pressure drop is. if you wanted to just make up some numbers as an example you could say that the main jet delta p on the VM22 was, lets say, 10 cm. So then the 65% increase on the VM18 needs the pressure to to be (10/.45)= 22.2 cm differential to make the same mass flow rate. Now if you are .2 cm off on your float level, on the VM22 that will be a (.2/10) =2 % change in mass flow rate, whereas if you are .2 cm off on the VM18 it will be a (.2/22.2)= 0.9% change in mass flow rate.

I think that math is right but i'm not super sure that you can use the mikuni jet size flow rates in a linear fashion like that, either way it shows a pretty good example of how the original poster is way the fuck wrong.

Re: Importance of float level

> Graham Motzing Wrote:

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

> EX:

>

> just after posting i remembered a really good example of this. Due to

> manifold constraints and packaging i went from a VM22 on a moped build

> to a VM18. Despite being similar design and layout, these two carbs are

> (obviously) different castings and always end up running really

> different tuning parts.

>

> I had a 165 jet in the VM22, when i put the VM18 i was running a 75 jet.

> since mikuni jets are sized based on fuel flow, its easy math to see

> that dropping the jet size resulted in a (1-(75/165))= 65% decrease in

> flow rate through the jet.

>

> now, the speed of the moped didn't decrease much, and it was properly

> tuned in both scenarios, which means we can assume that mass air flow

> rate stayed relatively constant and fuel flow rate stayed relatively

> constant.

>

> so, because mikuni did the hard work for us and linearized the mass fuel

> flow rate of the jets, the math is really easy to say that (give or

> take) there was a 65% increase in differential pressure across the main

> jet to accomplish the same mass fuel flow rate with a smaller jet.

>

> so the differential pressure of having a different float level setting

> as a percentage change in mass fuel flow rate decreased by a factor of

> whatever that pressure drop is. if you wanted to just make up some

> numbers as an example you could say that the main jet delta p on the

> VM22 was, lets say, 10 cm. So then the 65% increase on the VM18 needs

> the pressure to to be (10/.45)= 22.2 cm differential to make the same

> mass flow rate. Now if you are .2 cm off on your float level, on the

> VM22 that will be a (.2/10) =2 % change in mass flow rate, whereas if

> you are .2 cm off on the VM18 it will be a (.2/22.2)= 0.9% change in

> mass flow rate.

>

> I think that math is right but i'm not super sure that you can use the

> mikuni jet size flow rates in a linear fashion like that, either way it

> shows a pretty good example of how the original poster is way the fuck

> wrong.

I’m definitely wrong too!

Re: Importance of float level

> Graham Motzing Wrote:

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

> 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.

Agreed, as long as they stick to their respective field of study.

Re: Importance of float level

Fuel is delivered to the engine by the carburetor, which is a very technical pumping mechanism with a miniature piston inside, the other many components, each of which is required for the proper functioning of the whole work in combination to produce a fluid flow of air fuel mixture using the Dr.Phil Bernoulli's principle. When the crankshaft spins, the offset lobes carrying the journals set up harmonic vibrations in the cases and cylinders. These vibrations cause air to be sucked out of the combustions chambers in the carburetor, past the fanoutinizer rings which act like one-way valves in much the same manner as the reed valve in a diaphragm pump. The air is then stored in transfer jets which act as a energy reservoir and can hold tremendous pressure. Because there are at least two transfer jets and fuel reservoirs this also provides and equalized balance to the engine. These jets are opened up when an engine is blueprinted and balanced and sometimes more are added for added boost.

By inverting the carburetor it raises the differential pressure between the venturi and the outside atmospheric pressure to allow more fuel to flow from the diffuser assemblies into the combustion chambers of the carburetor. To offset this you need to understand the Gopenheizer principal of pressure differentials where the sum of half the displacement of a vacuum chamber is equal to the square of the surrounding vacuum level in microhales. So basically you would need to use a drill that is 3.4 times the differential between the smaller jet and larger jet.

To compensate for the drop in medial cross section flow you will need to use a W37 diffuser and a Y37 air correction orifice and set your needle on either the 6th or 7th groove, depending on the air temperature, usually above 20°c you would need to use the 7th groove or switch to a shorter taper and a Q43 slide if it still bogs on the corners or weeps fuel out of the over flow.

You also might have to put in a third anti-percolation disc if the fuel foams out the overflow or the float valve does not want to prevent flooding, which can happen if the Gopenheizer K value is above 34 microhales in your calculations.

On the intake stroke of the two stroke engine the piston in the carb created a vortex of fuel that is forced by hydraulic induction through a jet. This jet is called the main jet and is aimed directly down the intake towards the spark plug. The jet must produce a lot of pressure in order to overcome the pressure differential which holds the engine ports open. If the jet of fuel is too low it will not spray onto the sparking plug and you need to adjust the angle of the jet to either "up jet" or "down jet".

There is also a choking mechanism on all carburetors which narrows the bore of the carburetor so the pressure differential between the compression stroke and the atmospheric pressure increases. This in turn makes the piston inside the carburetor move faster and pump more fuel through the jet at the spark plug. Excessive use of the choke will make the spark plug a darker colour because of the dark blue tint or dye in the oil that is mixed with the gasoline. This can be remedied by doing a plug chop, where you make the spark plug shorter by chopping off a section of the electrode which will expose some clean electrode.

On many engines there is a decompression or starter valve, these valves are placed in the engine on the exhause side of the combustion chamber. When you start the engine you need to open the decompressor valve. What that does is allows some of the stored up energy in the exhause pipe to go back into the combustion chamber. Because you need the choke on ful to start the differential in pressure forces more fuel directly at the spark plug so that when it ignites it will continue to travel across the combustion chamber creating multiple combustions. The stronger combustions will form until there are two simultaneous combustions (for a two stroke engine, 4 combustions for a 4 stroke, etc) which will allow the engine to run without the choke and send the energy charge into the exhause. This energized exhause will ignite the first charge of fuel that enters the combustion chamber, starting the flame kernel which will light each subsequent power charge entering the chamber. Once the engine is running you close the valve, trapping the fire in the combustion chamber where it will contunue to burn the fuel as it comes in. To shut off the engine you just need to open the valve, this will syphon off some of the flaming fuel into the exhause, where it will be stored up for the next time you need to start the engine.

Re: Importance of float level

Can’t you just go away, in your somewhat obscure country that’s a size of one of one county if that in one state or 1 city in a state of USA and just say nothin!

Just because you live in in a tiny little area and you think you so know so much about carburetion, where you are you living is nothing compared to like 3-4,000 miles of open road where I live! You don’t think we know what float level or anything common carb stuff? Come on !

Just go away and imagine that you live somewhere were you can go 3 to 4000 miles nonstop, instead of the a few KM your allowed in your suck ass socialist/hi tax country that tracks you you wherever you go!

Man it sucks to be over there but maybe pretty soon we may we may be like you and suck beyond believe because no one wants to work and get free money for nothin, but for now it’s sweet until some moron gets voted in who is a dumbass!

With a bike and or one of my vehicles and can go 3000 miles or more without anybody bothering me! And gas is only 2,30\$ a gal,

Can you go that far? Where you are are gas prices that cheap? Can you go a week or two without posting dumb already known here for 20 years?

I don’t think you know what you’re posting because you live in a fishbowl!

I forgot 10 times what you’re posting over 40 years, so can you go away please!

I mean what you’re posting is what a noob would be posting 20 years ago!

Sorry to burst your bubble :)

Re: Importance of float level

When I rebuild carbs, I Google what the float setting should be, then check it with a worn out ruler, almost never have to adjust it, then I put it on my bike and go riding.

Re: Importance of float level

Gotta Admit, I live for "DR. Rebel's" "replies" to these threads and the ensuing responses from the other folks who either "get it" or "Don't", hahahahahaha..

Re: Importance of float level

Like putting a LT4 into a Opel GT...

...its either real or wish it was real...

> Norris Hall Wrote:

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

> Gotta Admit, I live for "DR. Rebel's" "replies" to these threads and the

> ensuing responses from the other folks who either "get it" or "Don't",

> hahahahahaha..

Re: Importance of float level

Well I can guarantee that if it is in fact real the only thing left that's Opel GT is the shell.

Re: Importance of float level

And hopefully they were smart enough to put about a thousand pounds of ballast above the rear axle...

Re: Importance of float level

> Rebel Moby Wrote:

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

> Like putting a LT4 into a Opel GT...

>

> ...its either real or wish it was real...

>

> > Norris Hall Wrote:

>

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

>

> > Gotta Admit, I live for "DR. Rebel's" "replies" to these threads and

> the

>

> > ensuing responses from the other folks who either "get it" or "Don't",

>

> > hahahahahaha..

That looks like Stacy David built that. He always has a crazy old school garage layout for his filming

Re: Importance of float level

1:25 scale model - a hobby of mine

Re: Importance of float level

I build models as a hobby, goodly fun

Re: Importance of float level

Haha, that's great! I had not clicked on the picture and my laptop screen is just small enough. Of course now that I know I can see it looking closer. Cool set up! I have possibly the same still in the box! ERTL 1:25

Re: Importance of float level

I have the AMT Original Art Series one. Came with the 4 banger and a V6 so I decided to throw in a spare vette motor I had...

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