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What is being called a VM series is just a plain old fashion venturi single stage slide carburetor with a float bowl to control fuel delivery and if you bought a 2021 2-stroke race bike today, that is what will be on it, there is no modern carburetor equivalent. only various models by various manufacturers.
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CV refers to Constant Velocity carburetors and there is a huge difference except for the fact that carburetors operate better if they can draw from a large volume of reasonably still clean air and can breathe through a velocity stack which is just like a funnel, a funnel that makes the air flow in a linear direction, not turbulence. Turbulence is exactly why a velocity stack exists, turbulence at the intake creates inefficiencies. Anybody that doubts it only needs to look at the shape of the rubber horn they took off to stick the cheap pod filters on.
 

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I am not arguing Velocity stacks, they are more efficient. CV carburetors have an inherent lag and are more suited for general riding. You can sharpen them up with velocity stacks but you can never take the diaphragm lag out of them. Racing is another thing altogether. Flat slides would probably be a better choice if you are made of money and want to run a naturally asperated carburetor.
 

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I am not arguing Velocity stacks, they are more efficient. CV carburetors have an inherent lag and are more suited for general riding. You can sharpen them up with velocity stacks but you can never take the diaphragm lag out of them. Racing is another thing altogether. Flat slides would probably be a better choice if you are made of money and want to run a naturally asperated carburetor.
CV carbs are the epitome of carburetor design complexity that was always driven by the increasing need to reduce fuel consumption on the end product. The reason they are disappearing is because fuel injection is superior at everything, and now manufacturers are even starting to make that vacuum controlled.

I'd be just as happy with a round slide on my race bike, makes little odds, I know I could make it work with either one, the Reed Valves are more important on a 2-stroke.
 

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If you believe you can remove that part and still make it work right you are wrong.
Only when relatively new. At least that's been my experience with rubber parts like that.
 

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Oh, I shouldn't get into this... :rolleyes:

I am not arguing Velocity stacks, they are more efficient. CV carburetors have an inherent lag and are more suited for general riding. You can sharpen them up with velocity stacks but you can never take the diaphragm lag out of them.
You can 'tune' the rate of lift (or call it timing of lift) of the CV slide by modifying the lift hole and using different strength springs. With enough experimentation you can make it do anything you want. (You'll end up buying several slide assemblies and springs before you're done). Probably not needed for a stock engine where you've only removed the air box and piped it though.

If you believe you can remove that part and still make it work right you are wrong.
The right way to do it is to tune the total intake length (center of intake valve to velocity stack / carb inlet) to the RPM you want the best efficiency. You have to consider space limitations so you probably can not catch the ideal sonic wave.
The 'lag' is likely due to improper jetting.

S F
 

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Only when relatively new. At least that's been my experience with rubber parts like that.
You totally misread the intent of what I wrote there. People are removing that part to put a cheap pod filter directly onto the throat of the carburetor, and there is still nothing wrong with that 40 year old rubber velocity stack I posted a photo of, it's going back on a Suzuki and will likely out live me.
 

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It's called a Venturi carburetor for a reason, but if you discard the cone shape on the left side of the red arrow, you got nothin left of the venturi effect, you have intake turbulence where you don't want it. Why would one fix that by dumping more fuel into the engine.
 

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O Scope,
The cone shape on the left side of the red arrow (in your diagram) is part of the carburetor, not an add-on and not removable.
The venturi effect happens inside the carburetor and is part of the original design of the carburetor.
The venturi effect is not dependent on anything beyond the rear part of the carburetor itself because the venturi effect happens inside the carburetor itself.

S F
 

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Half Speed,
that's as ridiculous as, "can not catch the ideal sonic wave" why are you still trying to explain away the velocity stack intake shape that was so obviously removed? A velocity stack is a funnel, do you know what a funnel does? The hacks removed all the air funnels from the carburetors and now the engine runs like garbage same as it would with open throat carburetors, so next they try opening the holes where the raw fuel enters in an attempt to compensate for what they Think must be too much air getting into the carburetor. <- That ain't how it works.
A carburetor is a fuel atomizer and you just made your fuel atomizer work poorly, if the air intake stack was not needed Suzuki could save a lot of money leaving it off and I bet the bike did work good at one time with the original parts in place.

... I can only image what they did for crankcase ventilation when they discarded the air box. Probably stuck a tiny pod filter on that too, which will quickly plug from the inside.
 

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Oh, I shouldn't get into this... :rolleyes:
........ Because some may not understand and become hostile. :(

Half Speed,
that's as ridiculous as
, "can not catch the ideal sonic wave" why are you still trying to explain away the velocity stack intake shape that was so obviously removed?
What is ridiculous? I only explained where the venturi effect happens. Maybe I should have explained what a venturi is but I assumed you knew because of the diagram you harvested from the innerweb.
Because of your 2-stroke engine experience I also assumed you would know what a sonic wave (sound wave) is because expansion chambers are designed around them and rely on them to function best at a desired RPM range.
There are simple formulas for determining the ideal tuned intake tract length for a four stroke engine using SONIC WAVES that are created in the intake tract of an engine. I'm sure you can find information on the web about it if you're interested. It is not ridiculous. It is fact.

The hacks removed all the air funnels from the carburetors
Funnels are not necessary and many factory induction systems use straight air ducts, not velocity stack type funnels behind the carburetor. Again, the correct intake tract length is more important than a funnel behind the carburetor. A straight air duct serves the function of reducing turbulence at the air jets in the back of the carburetor and to establish a more ideal overall intake length. I do agree some cone shape is more ideal than a straight duct behind the carburetor but again, it does not contribute to the venturi effect.

This is a Suzuki photo thread. We should stop "debating" basic tuning here.
You should start a thread on carburetor design, function, air flow dynamics, basic performance tuning and such if you want to carry on further.
I have suggested that before.... I will contribute. :)

S F
 

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Hi all. Name is Chris and I'm coming back into riding after over 25 years in a cage. Stopped riding because I had to wear some pretty intense glasses that cut my peripheral vision down to unsafe levels for riding. Now that I was able to obtain some serious contacts, my love for being on two wheels has blossomed. Used to work at a cycle salvage and built my share of bikes. Love Japanese vintage stuff even though the new generation of bikes are better by a lot. I'm 61 and grew up riding 'less than refined' sport bikes so in my search for a new toy, I decided to go with this little rare machine.
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This was taken before I began my detail and restoration project that I plan to continue during the winter.
 
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