Quote:
Originally Posted by Jiggles
........Now I'm quite a carb n00b so forgive me if I'm naive in saying, wouldn't you HAVE TO open up the airbox and increase the airflow in order to get more power?........
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You wouldn't have to, but reducing resistance and friction by increasing traverse sections always increases volume of air moving between two pressures.
The dilemma with the Venturi portion is that increasing the section reduces the suction effect and the fine control at low flow conditions.
Our carburetors are a compromise for fuel economy and proper control during a huge range of riding conditions.
Special purpose carburetors are only good for that specific purpose and perform marginally for the rest.
No Venturi for EFI, means that engine breathing can be improved.
Copied from
http://faq.ninja250.org/wiki/How_a_c...eat_Compromise
"VARIABLE VENTURI - Getting Sucked In
A venturi is a tube with a convex taper, (one end wider than the other). As air enters the wider end it's squeezed into the narrower section of the tube, lowering the air's pressure. The area of lowest pressure is just past the narrowest point and is called the depression. This has always seemed counterintuitive, but Bernoulli's Principle outlines the fluid dynamics involved in this effect. This lowered pressure, or comparative vacuum, is separate from the engine vacuum. A variable venturi varies the venturi diameter at the depression by raising or lowering an obstruction. This obstruction is called a slide. On a CV the slide is called a piston or diaphragm valve.
CV or SLIDE CARB - The Great Compromise
Both the CV and conventional slide carbs are classified as variable venturi carbs. The slide on a conventional carb is directly connected to the throttle cable. Twist the throttle grip and the slide is raised in the venturi. On a CV carb the throttle cable is connected to a butterfly valve that varies the volume through the venturi. It's not the throttle, it's the pressure difference from the venturi to the outside atmosphere that moves the slide.
So which type is better? That depends on what you want to do. The manufacturers will tell you the CV is the next best thing to electronic fuel injection. It does feed a precise amount of mixture to smooth out throttle response, reduce pollution, and stretch your fuel budget and gas tank range.
This is great for tarmac cruising and feeling warm and fuzzy about doing your part to reduce global warming while pocketing some spare change. It sure makes it easier for the manufacturers to get the EPA approval stamp on the bike.
But what if you feel that no matter how much you hop up your little beast, you're never going to match the belching of that cager in the gas guzzling V-12 ? What if you don't mind spending more for gas, and when you go off-road you want a burst of power to blip over obstacles or steer through a wash without fanning your clutch while waiting for the vacuum to build in the venturi? If you can discipline yourself to control the throttle so that you don't bog your engine, then you want a conventional slide carb.
40 MM - Size Matters
With the same engine and carb design, a 38mm diameter venturi will more accurately meter the mixture on the low end, while a 41mm diameter will do a better job of supplying mixture at higher engine speeds. It's another factor to consider if you replace your carb."
Link to original page on YouTube.