Carburator Chart (and info)

I thought I'd throw this picture in to help visualize how a carburator atomizes

fuel prior to the intake manifold of the engine.

What mechanics forget when dialing in their motor is that the needle position (clip height)

is what governs the bottom end power of the engine.  In other words, by adjusting the clip height on

the needle up or down, the motor will in turn run leaner (needle raised) or richer (needle lowered).

Keep in mind that needle clip position height does affect idle a little more than the chart below indicates

because the needle is essentially raised from the main jet seat by a fraction; thus, providing more fuel on idle.

Many power hungry ATV enthusiast tend to add performance modifications to their machines

(i.e. slip-on pipe) without considering adjusting the delivered fuel for the entire powerband.  These self-motivated

garage mechanics try to adjust for the motors demand for fuel by increasing the size of the main jet,

but forget to move the needle position.  This is a mistake.  The chart below clearly illustrates that the main jet

delivers fuel only for 75%-100% throttle, this is why it is important to also consider the needle height

position.

In summary:

air screw position for ~0-5% throttle (can be adjusted on carb if idle low or high)

throttle cutout for ~5-15% throttle (no adjustment; this is designed in carb by manufacture)

clip position on needle to control needle height for ~15-30% throttle (can be adjusted if carb is

sluggish when you thump the throttle)

needle taper for ~30-75% (no adjustment; however, DynoJet manufactures different tapered

needles for OEM carbs)

main jet for ~75-100% throttle (only way to install correct size main is to warm up engine,

run quad in top gear for ~20sec., shut motor down by engine cutoff switch on handlebars and coast to stop,

pull plug and look at color).  Brown/Black plug = rich; white plug = lean.

Then, ask yourself, did the motor bobble during top gear run, or was the motor sluggish and didn't seem

to pull?  If your answer is bobble, then your too rich on main (drop main jet size).  If your answer is

sluggish, increase one size bigger for main jet.

Hope this was informative, happy motoring!

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