Mikuni Tm 38; Carburetor Overview - Polaris 340 CLASSIC 2006 Manual

CARBURETION

MIKUNI TM 38

CARBURETOR OVERVIEW

The advantages of the TM flatslide system include improved
throttle response and a significant reduction in throttle effort
due to rack style carbs and the use of cable cam. The
following are the main components of TM carburetors and the
functions of each components.
Pilot Air Jet (A): The pilot air jet controls the amount of air
entering the engine in the idle circuit. The pilot air jet size is
imprinted on it. Bigger pilot air jets allow more air to enter,
leaning the idle mixture. If engine loads up at idle, first try
turning fuel screw in. If not correct, try larger pilot air jet.
Starter Jet (B): The starter jet's function is to meter fuel
entering the engine when choked. Larger numbered starter jets
pass more fuel, therefore more fuel will enter the system when
jetting to a larger size. Like the pilot air jet, the jet size is
imprinted.
Jet Needle (C): The jet needle performs the same functions as
on Mikuni VM carburetors. However, the needles in the TM-
38 carburetors are longer and are not interchangeable with
VM needles. To raise or lower the needle, remove the top cap
(D) and loosen the 2.5mm Allen screw holding the needle in
4.6
place. Reach inside with a long nose pliers and pull the needle
out. The C-clip can then be adjusted for the desired effect.
Needle Jet (D): The needle jet is press fit into carbs and is not
replaceable.
Piston Valve or Throttle Valve): The throttle valve controls
the rate of engine air intake by moving up and down inside the
main bore. At small throttle openings, air flow control is
performed chiefly by the cutaway. By controlling air flow the
negative pressure over the needle valve is regulated, in turn
varying the fuel flow
Main Jet and Pilot Jet (F): The main jets (hex) and pilot jets
(air bleed type) are identical in style and function as the
Mikuni VM carbs. There is washer on main jet that is staked
and should not come out. The part numbers for main jets and
pilot jets are the same as Mikuni VM round slide carburetors.
Fuel Screw (G): The fuel screw controls the low speed air/
fuel mixture at idle. Turning the fuel screw out makes the
mixture richer and can be adjusted up to five turns out.
Float/Needle & Seat Assembly (H): The float/needle & seat
are sold as an assembly and cannot be replaced as individual