So which type is better? That depends on what you want to do. It's not the throttle, it's the pressure difference from the venturi to the outside atmosphere that moves the slide. On a CV carb the throttle cable is connected to a butterfly valve that varies the volume through the venturi. Twist the throttle grip and the slide is raised in the venturi. The slide on a conventional carb is directly connected to the throttle cable. On a CV the slide is called a piston or diaphragm valve.īoth the CV and conventional slide carbs are classified as variable venturi carbs. A variable venturi varies the venturi diameter at the depression by raising or lowering an obstruction. This lowered pressure, or comparative vacuum is separate from the engine vacuum. This has always seemed counterintuitive to me, but Bernoulli's Principle outlines the fluid dynamics involved in this effect. The area of lowest pressure is just past the narrowest point and is called the depression. As air enters the wider end it's squeezed into the narrower section of the tube, lowering the air's pressure. Primary type carbs use a solid jet, (no pin holes).Ī venturi is a tube with a convex taper, (one end wider than the other). These pin holes allow air from the air jet to premix with fuel from the fuel jet to start the mixture emulsification process before it enters the venturi.

Most 4-strokes have pin holes along the length of this brass jet. On the CVK40 it consists of a collar and what Kawasaki calls a holder. The 40 in the name represents a 40 mm venturi exit diameter. It's also known as Constant Depression or Constant Vacuum.

The CVK40 is technically a bleed type carb, with a variable venturi that's controlled by constant velocity (CV). They will be less expensive than ordering through your Kawasaki dealer and, in most cases they will be 'in stock'. If you need replacement parts you'd be well advised to get them from your local Harley Davidson outlet. While most of the following information applies to all CV carbs, and to some extent all carb types, this article is specific to the Keihin CVK40 found on many Kawasaki motorcycles (KLR's and Vulcans) along with some Harleys.

Keihin cr special carb tuning