Service Manual

ManualsBrandsToro ManualsSnow ThrowerToro 38536

CARBURETOR

Identification

The E series en

ines use two versions of the primer

start carburetor. One with an air filter box on the

mower en

ines (DuraForce) and one without an air

filter box on the snowthrower en

ines (R tek).

Differences include a plu

in the snowthrower

carburetor vent passa

e and some minor differences in

the throttle shafts, jettin

and throttle valve bleed hole.

Both carburetors have two circuits and use both a

choke and primer for startin

. (See Fi

ure 13.)

ure 13

0720-012

Theory of Operation

As the crankshaft rotates, the piston moves back and

forth in the cylinder, alternately creatin

a pressure or a

partial vacuum in the crankcase. (See Fi

ure 16.)

As the piston moves toward the spark plu

, the reed

valve opens (see Fi

ure 15) or the inlet ports are

uncovered (see Fi

ure 16). This causes air to rush

throu

h the carburetor throat to equalize the pressure

in the crankcase. The carburetor throat is formed into

a venturi (lar

e at each end but with a smaller center

passa

e). When air rushes throu

h the venturi, air

pressure at the center of the passa

e is lowered.

By insertin

a tube from the carburetor float bowl into

the venturi (see Fi

ure 14), the lower air pressure at

the venturi causes the normal air pressure in the bowl

to push fuel up the tube.

ure 14

3297-012

The fuel/oil mix is then picked up by, and mixed with,

the movin

air, the amount of fuel determined by

throttle openin

and jet size. This fuel/oil/air mixture

enters the crankcase throu

h the reed valves

(DuraForce), or ports (R tek). (See Fi

ure 15 and

ure 16.) When the piston moves away from the

spark plu

, the cylinder intake ports are opened and

the now pressurized crankcase causes the mixture to

move into the combustion chamber.

Reed Valve

ure 15

3297-021-3

Piston Ported

ure 16

3297-002

A. Venturi

B. Center Passa

e Area

C. Air Pressure

A. Reed Valve Closed

B. Exhaust Gases

C. Second Stroke

A. Intake Ports Closed

B. I

nition

C. Third Port Open

D. Partial Vacuum