Thread: Jetting 101
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Old 20-11-2006
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Keg Keg is offline
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Join Date: Apr 2002
Location: 2 Stroke Town
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Jetting 101

Here is a quick blurb on basic jetting - as discussed on the Jetting night in Melb last Friday. I will make further posts in this thread to expand on this but to ensure people learn the basics, I will only explain bit by bit!

Eventhough there are really a dozen parameters you can change in a carby, there are really only two basic circuits in a carby you should know about for tuning most bikes.

1) The Pilot Jet - squirts in fuel at and around idle
2) The Main Jet - squirts in fuel when you turn the throttle

The amount of fuel these put in can be regulated by simple adjustments.

There is a mixture screw that can be turned in or out on nearly all bikes to regulate this.

Most 4 strokes it is called a fuel screw and the more you turn it out the richer it gets. This is usually found towards the engine side of the carb at the bottom.

Most 2 strokes it is called an air screw and the further you turn it out the leaner it gets. This is usually found on the side of the carb towards the air box

DO NOT CONFUSE THESE WITH THE IDLE SCREW - usually a black plastic knob that just increases the revs (not the air/fuel mixture ratio).

This jet is regulated by the needle unblocking the fuel flowing through it. The mroe you turn the throttle the more fuel flows. You can lower the clip on the top of the needle to start the needle further out of the jets way making the fuel flow richer.
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