Main Jet; Jetting Guidelines - Polaris INDY TRAIL RMK Service Manual

FUEL SYSTEM / CARBURETION
The main system is designed to deliver fuel between
low speed and high speed operation. This system is
made up of the jet needle, needle jet, and main jet. The
main system begins to take effect as soon as there is
enough air flow into the carburetor venturi to draw fuel
up through the main jet and needle jet assembly. This
Throttle Valve
system works in conjunction with the needle jet sys-
Jet Needle
tem.
Air Jet
By-pass
During low speed driving, there is very little clearance
Pilot Outlet
between the jet needle and the needle jet; therefore,
very little fuel from the main jet can pass between the
jet needle and the needle jet. As the throttle valve
opening is increased, the tapered jet needle is raised
farther out of the needle jet, allowing greater fuel flow.
Pilot Jet
Under full throttle opening, the cross sectioned area of
Needle Jet
clearance between the jet needle and the needle jet
becomes greater than the cross sectioned area of the

Main Jet

main jet. Thus the main jet is now controlling the
amount of fuel flow.
Main Jet
When the throttle opening becomes greater and the
area between the needle jet and jet needle increases,
fuel flow is metered by the main jet. The number on the
jet indicates the amount of fuel CCs which will pass
through it in one minute under controlled conditions.
Larger numbers give a greater flow, resulting in a
richer mixture.
Main jets are screwed directly into the needle jet base.

Jetting Guidelines

Changes in altitude and temperature affect air density, which is essentially the amount of oxygen available for
combustion. In low elevations and cold temperatures, the air has more oxygen. In higher elevations and higher
temperatures, the air is less dense.
Carburetors on most Polaris models are calibrated for an altitude of 0-3000 ft (0-900 meters) and ambient temper-
atures between -20° to +10° F (-29° to -12° C). All carburetors must be re-calibrated if operated outside the pro-
duction temperature and/or altitude range. The main jet installed in production is not correct for all altitudes and/or
temperatures.
CAUTION:
A main jet that is too small will cause a lean operating condition and may cause serious engine damage.
Jet the carburetors carefully for elevation and temperature according to the jetting charts in this manual.
NOTE:It is the owner's responsibility to ensure that the correct jets are installed in the machine for a geographical
area. Be very careful when jetting down in warm weather. As the weather turns colder it will be necessary to re-jet
upward to prevent engine damage. When selecting the proper main jet always use the lowest elevation and tem-
perature that is likely to be encountered.
4.17