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New to carburetors, and need some basic info to get you
started? Check out our Jetting 101
page.
Need
jetting for a specific model? We have it
here
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If you are thinking about modifying your engine at
all, it is imperative to understand at least the basics of jetting.
Installing aftermarket components (such as exhaust systems, air filters, etc)
without re-jetting means you are giving up much of the performance offered by
these products - and could damage your engine.
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Install performance parts without
rejetting...
waste $$ and horsepower. |
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Failure to understand jetting can cost
you $$ |
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Piston and subsequent engine damage
caused by LEAN jetting |
JETTING GUIDELINES
These jetting specifications are
designed as a rule of thumb. They are in no way absolute. Variations in
air density, specific gravity of fuel, altitude and other engine
modifications play a large part in jetting. It is the responsibility of
the owner to determine proper jetting for their engine.
HOW TO JET - THE
BASICS
Plug reading doesn’t work. Revving
the engine while it’s sitting in the garage doesn’t work. Other than Dyno
testing, the steps below are the only way you can consistently jet your
engine.
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1. Find a gentle slope
that you can ride in 2nd or 3rd gear. Look for something that will
put a decent load on the engine. This will be your tuning test area.
2. Make the recommended jetting changes. Always start rich and work
leaner.
3. A basic outline of which jet is active at a particular throttle
setting:
Pilot Jet = 0 to 1/4 throttle. Needle = 1/4 to 3/4 throttle. Main
Jet = 3/4 to Full Throttle.
● Changing the Main Jet size won’t affect how your engine idles or
runs at 1/4 throttle.
● Engine RPM isn’t what determines which jet is active - only
throttle position does this.
4. Start and warm up the engine, then ride your ‘test hill’. Any
point where you feel the engine stumble or hesitate indicates a rich
condition. Note the throttle position and modify the corresponding
jet (1/4 to 1/2 throttle = leaner needle. 3/4 throttle or more =
leaner main jet).
5. Only change jetting by 1 step at a time, and 1 circuit at a time
(don’t change needle and main at the same time). Re-check after
every change.
6. Once the engine runs smoothly throughout, you’re jetted! |
If you
ever notice an abrupt change loss of power, or engine sounds changes, shut
it down.
Why not just sell a kit?
Although some companies offer "Jet Kits", Powroll believes it is
impossible to assemble a generic kit which will work for every bike in every
situation. We believe that customers looking for performance need to understand jetting in order to get any benefit from performance
modifications.
MORE HELP
Need
jetting for a specific model? We have it
here.
For engines with more
extensive Powroll modifications, or those which do not respond to the tuning
instructions that came with your kit, or to the suggestions listed above, please
contact our technicians at 541-923-1290.
If you are not running Powroll components, we will not be able
to answer your jetting questions.
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WHAT KIND OF FUEL? |
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'Race Gas Required' or 'Race Gas Mix Required' means high octane
There are new fuels designed to get the best power
possible from STANDARD compression engines. These may not be
high octane.
Occasionally, you will hear people say oxygenated fuels are the only
fuels you should run in a four stroke -- NOT TRUE. You should
match the fuel octane to your compression ratio, no matter what 'type'
of fuel you use.
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Rule of Thumb:
≠
If engine is OK on premium pump gas - lower
octane specialty fuels OK.
Ó
If engine compression is too high for
premium pump fuel - DO NOT run lower octane fuels.
If you'd
like to learn more about octane, check out our
Tech page.
For information about specific companies fuels:
Nutec
Sunoco (Cam2)
Trick
VP
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