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Yamaha Factory Racing Complete Aragon Test
Yamaha Factory Racing Complete Aragon Test
Posted 686 days ago

The Yamaha Factory Racing team wrapped up a successful one-day test at the Aragon Motorland circuit today. Riders Ben Spies and Jorge Lorenzo spent the sessions re-confirming areas tested in…

Kawasaki leads GEICO EnduroCross Manufacturers Championship
Kawasaki leads GEICO EnduroCross Manufacturer…
Posted 688 days ago

One-Two finish at the Vegas opener gets Kawasaki off to a good start

Irvine, CA (June 5, 2012) – For the first time, the 2012 GEICO AMA EnduroCross series will include…

Kawasaki leads GEICO EnduroCross Manufacturer…
World Superbike Round Seven Marks Halfway Point For KRT Duo
World Superbike Round Seven Marks Halfway Poi…
Posted 688 days ago

World Superbike, Misano Adriatico, Republic of San Marino, 5 June 2012
Tom Sykes (Kawasaki Racing Team) and his new team-mate Loris Baz will reach the halfway point of the World Superbike…

World Superbike Round Seven Marks Halfway Poi…
Ryan Dungey Earns First Motocross Win of the Season
Ryan Dungey Earns First Motocross Win of the …
Posted 688 days ago

Another history-making ride as he claims KTM’s first-ever U.S. 450 Motocross class win.
LAKEWOOD, ColoRADo – Red Bull/KTM Factory rider Ryan Dungey earned his first overall win of the Lucas Oil…

Ryan Dungey Earns First Motocross Win of the …
Jake Weimer Career Best Runner-Up Finish at Thunder Valley Motocross
Jake Weimer Career Best Runner-Up Finish at Thunder Valley M…
Posted 689 days ago

Kawasaki Supercross Report
Irvine, Calif. (June 4, 2012) - At a stormy Round 3 of the AMA Pro Motocross Championship at Thunder Valley MX in Lakewood, Colo., Monster Energy Kawasaki’s Jake…

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What It Does: A Motorcycle carburetor

Motorcycle Carburetors:

When people talk about jetting a Motorcycle carburetor and tuning a Motorcycle carburetor , they’re talking about manipulating the carburetor’s 4 main circuits to optimize gasoline delivery and therefore engine performance.

MX carb 300x300 What It Does: A Motorcycle carburetor

Dirt Bike Carburetor

Most motorcycle carburetor circuits are governed by throttle position and not by engine speed. They might adjust the air screw, adjust the jet needle’s clip position or exchanging the pilot (slow) jet, main jet, throttle valve (slide) or jet needle for one of an appropriate size. A perfectly tuned 2-stroke engine/carburetor delivers a 12.5 to 1 air to fuel ratio.

If you look at a Motorcycle carburetor, you will notice a rather large hole going from one side to the other. This is called a Venturi. Air passes into the engine through this hole (Venturi).

As the velocity of the air entering the carb (and then the engine) increases, it’s pressure decreases, creating a low pressure or vacuum in the venturi. This vacuum moves around in the venturi, as the throttle is opened, and sucks gasoline through the different jets in the carb. The gas then mixes with the air going through the venturi.

The way the Motorcycle  jets are made causes the fuel to vaporize as it goes into the venturi. Where the jets are placed in the carb and where the jet’s outlet is located in the venturi, determines what part of the throttle opening that jet controls.

The idle jet system (comprised of pilot air jet, pilot fuel jet and pilot fuel screw) controls from 0% to about 25% of the throttle opening.

The throttle valve controls 0% to 35% of the throttle opening. The needle jet and jet needle control from 15% to 80% of the throttle opening and the main jet controls 60% to 100%. This means that when you open the throttle about one eighth of the way open, all of the gas/air mixture going into your engine is controlled by the idle jet.

The jet needle starts to effect things before the effect of the idle jet ends. This is something to remember when working on carbs… everything is interconnected. Change one thing and it will effect other things.

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