FUEL SYSTEM

3
B

CARBURETOR
Table of Contents
Page
Fuel System Troubleshooting . . . . . . . . . . . . . . 3B-1
General Information . . . . . . . . . . . . . . . . . . . . 3B-1
Carburetor 9.9 HP . . . . . . . . . . . . . . . . . . . . . . . . 3B-4
Carburetor 15 HP . . . . . . . . . . . . . . . . . . . . . . . . 3B-6
Carburetor Adjustments . . . . . . . . . . . . . . . . . . . 3B-8
Adjusting Pickup Point . . . . . . . . . . . . . . . . . 3B-8
Adjusting Idle Mixture Screw . . . . . . . . . . . . 3B-8
Adjusting Idle Speed . . . . . . . . . . . . . . . . . . . 3B-9
Carburetor Float Adjustment . . . . . . . . . . . . 3B-9
Adjusting Float Height . . . . . . . . . . . . . . . 3B-9
Adjusting Float Drop . . . . . . . . . . . . . . . . . 3B-9
Fuel Bowl Installation . . . . . . . . . . . . . . . . 3B-9
High Altitude Jet Chart . . . . . . . . . . . . . . . . . 3B-9

3B-0 - FUEL SYSTEM 90-855906 JUNE 1997

Fuel System
1. Propeller
Troubleshooting
2. Spark Plugs
3. Ignition Spark Voltage
General Information
4. Cylinder Compression
Problems that are thought to be caused by the fuel
5. Reed Valves
system may, in reality, be something completely dif-
ferent. Items, that are shown in the list on the right, Typical symptoms and solutions in troubleshooting a
could give the impression that there is a problem in fuel system are shown below:
the fuel system.
Problem: Engine Turns Over but Will Not Start or Starts Hard When Cold
Possible Cause Corrective Action
Improper starting procedure used. Review starting procedure as outlined in “Operation
and Maintenance Manual”.
Fuel tank empty or too low. Improperly mixed fuel. Check fuel in tank and replace or add whichever is
Contaminants (water, dirt, etc.) in fuel. necessary.
Fuel tank air vent closed or restricted. Check air vent on fuel tank. Air vent must be open
all-the-way and free from any contaminants.
Pinched, cut, restricted fuel line or loose fuel line Inspect all fuel lines and replace as needed. Tighten
connection. fuel line connections.
Dirty or restricted fuel filter. Inspect and replace or clean all fuel filters.
Needle and seat in carburetor that is either stuck Disassemble and clean carburetor.
open (flooding) or closed (no fuel).
Improper carburetor jet, restricted jet or idle mixture Refer to carburetor adjustments in this section.
screw out of adjustment.
Improper float level. Refer to carburetor adjustments in this section.
Low fuel pump pressure. Inspect Fuel Pump, replace reeds/diaphragm as re-
quired.
Carburetor loose on intake manifold. Check tightness of carburetor nuts.
Reed block loose or gasket defective. Using a pressure oil can apply 2-cycle oil around
reed block housing/crankcase housing matching
surfaces and carburetor base. If engine RPM
changes, tighten bolts/nuts or replace gaskets as
required.
Damaged fuel pump diaphragm. Refer to “Fuel Pump” section.
Off idle holes plugged. Blow with compressed air.
Main nozzle or idle nozzle air bleed holes plugged. Blow with compressed air.
Damaged reeds. Refer to “Reed Valve Assembly” section.
Fuel pick-up outlet tube in fuel tank cracked. Replace.

90-855906 JUNE 1997 FUEL SYSTEM - 3B-1

Problem: Engine Floods
Possible Cause Corrective Action
Dirt or debris are preventing inlet needle from seat- Flush out inlet seat and clean inlet needle.
ing.
Worn inlet needle. Replace.
Punctured float. Replace.
Incorrect float setting. Reset float.
Recirculation system check valves clogged. Clean or replace.

Problem: Engine Runs Too Rich

Possible Cause Corrective Action
Fuel level too high. Reset float to correct level.
Carburetor floods. See preceding “Engine Floods.”
Idle nozzle air holes plugged. Blow out with compressed air.
Restricted air flow. Inspect cowl air inlet and carburetor for obstructions.
Main fuel jet loose. Retighten jet.
Recirculation system check valves clogged. Clean or replace.

Problem: Fuel Blow-back Out of Carburetor

Possible Cause Corrective Action
Chipped or broken reeds on reed block. Replace reeds.
Excessive pre-load on reeds. Replace reeds.

Problem: Engine Runs Too Lean

Possible Cause Corrective Action
Carburetor is loose. Tighten bolts securely.
Fuel level is too low. Reset float level.
Clogged high speed jet. Inspect jet for varnish or debris and clean.
Restricted fuel flow to carburetor. Check fuel lines and filter(s) for restricted flow.
Incorrect high speed jet. Refer to main jet chart and replace with proper jet.
Idle mixture set too lean. Adjust to run richer (turn idle mix screw counter-
clockwise).
Air leakage into fuel system. Inspect fuel line connections, hose clamps, fuel
pump and fuel outlet tube (located in fuel tank) for
loose fittings.

3B-2 - FUEL SYSTEM 90-855906 JUNE 1997

Notes:

90-855906 JUNE 1997 FUEL SYSTEM - 3B-3

Carburetor 9.9 HP

1 2

22
27 23

20 26 16
21 15

4
3

28 25
6
7
24
18
19
17

10
9

5 30
29

12

33
14
32

31
11

14

13

3B-4 - FUEL SYSTEM 90-855906 JUNE 1997

 Carburetor 9.9 HP
TORQUE
REF.
REF
NO. QTY. DESCRIPTION lb. in. lb. ft. N·m
1 1 PLUG-By Pass Chamber
2 1 TUBE-By Pass
3 1 BALL-Choke Friction
4 1 SPRING-Choke Friction
5 1 SHAFT-Choke
6 1 SHUTTER-Choke
7 1 SCREW-Choke Shutter
8 1 PLUG-Body Channel
9 1 FLOAT-Fuel Bowl
10 1 PIN-Float
11 1 BOWL-Fuel
12 1 GASKET-Fuel Bowl
13 1 SCREW-Fuel Bowl
14 2 GASKET-Fuel Bowl
15 1 NEEDLE-Idle Mixture
16 1 SPRING-Idle Mixture Needle
17 1 NEEDLE-Inlet (Do NOT Remove Inlet Seat)
1 JET-Main (.049) (0 - 2500 Ft.)
OPT JET-Main (.047) (2500 - 5000 Ft.)
18
OPT JET-Main (.045) (5000 - 7500 Ft.)
OPT JET-Main (.043) (7500 - 10000 Ft.)
19 1 NOZZLE-Main
20 1 LINKAGE-Throttle Cam Follower
21 1 SHAFT-Linkage
22 1 E RING-Linkage Shaft
23 1 WASHER-Linkage Shaft
24 1 SHAFT-Throttle
25 1 SPRING-Throttle Shaft
26 1 SHUTTER-Throttle
27 1 SCREW-Shutter
28 1 LINK-Throttle
29 1 RETAINER-Choke Rod
30 1 ROD-Choke
31 1 INSERT-Choke Knob
32 1 KNOB-Choke
33 1 BUSHING-Choke Rod

90-855906 JUNE 1997 FUEL SYSTEM - 3B-5

Carburetor 15 HP

26 20

24 23

27 25 1 29 7

28

14
5
2

21 24
16

2
4 2
22 3

15
6
18 9
17
7
8

19 11

33
13

10

32
13
34 12
31
30

3B-6 - FUEL SYSTEM 90-855906 JUNE 1997

 Carburetor 15 HP
TORQUE
REF.
REF
NO. QTY. DESCRIPTION lb. in. lb. ft. N·m
1 1 PLUG-By Pass Chamber
2 4 BALL-Body Channel Plug
3 1 BALL-Choke Friction
4 1 SPRING
5 1 SHAFT-Choke
6 1 SHUTTER-Choke
7 2 SCREW-Shutter
8 1 FLOAT-Fuel Bowl
9 1 PIN-Float
10 1 BOWL-Fuel
11 1 GASKET-Fuel Bowl
12 1 SCREW-Fuel Bowl
13 2 GASKET-Fuel Bowl Screw
14 1 ELBOW
15 1 SCREW-Idle Mixture
16 1 SPRING-Idle Mixture Screw
17 1 NEEDLE-Inlet (Do NOT Remove Inlet Seat)
1 JET-Main (.070) (0 - 2500 Ft.)
OPT JET-Main (.068) (2500 - 5000 Ft.)
18
OPT JET-Main (.066) (5000 - 7500 Ft.)
OPT JET-Main (.064) (7500 - 10000 Ft.)
19 1 NOZZLE-Main
20 1 JET (.048)-Idle Air Bleed
21 1 JET (.047)-Throttle
22 1 SCREW-Throttle Jet Sealing
23 1 LINKAGE-Throttle
24 2 CLIP-Throttle Linkage Shaft
25 1 WASHER-Throttle Linkage Shaft
26 1 LINK-Throttle
27 1 SHAFT-Throttle
28 1 SPRING-Throttle Shaft
29 1 SHUTTER-Throttle
30 1 INSERT-Choke Knob
31 1 KNOB-Choke
32 1 ROD-Choke
33 1 RETAINER-Choke Rod
34 1 BUSHING-Choke Rod

90-855906 JUNE 1997 FUEL SYSTEM - 3B-7

Carburetor Adjustments Adjusting Idle Mixture Screw
Adjusting Pickup Point IMPORTANT: Turn idle mixture screw carefully,
do not force needle into seat.
1. Loosen screw on roller assembly.
1. Turn idle mixture screw in (clockwise) until lightly
seated in carburetor.
b
a

56189
c - Idle Mixture Screw
a - Screw, Roller Assembly
b - Mark On Throttle Cam
2. For both the 9.9 and 15 HP motors open idle mix-
2. Advance the throttle control lever until roller is ture screw 1-1/2 turn (counterclockwise).
aligned with mark on throttle cam. 3. Start motor and allow to warm up to operating
3. Turn the screw on roller assembly in (clockwise) temperature.
until it touches the throttle cam. 4. Move throttle lever to shift position and shift into
NOTE: The throttle shaft must move as soon as the forward gear. Rotate throttle grip to idle speed.
throttle linkage begins to move. If not, repeat steps 1 5. Slowly turn the idle mixture screw in (clockwise)
through 3. until the motor starts to misfire or stall due to a
lean mixture. Note the position of the screw slot.
6. Turn the idle mixture screw out (counterclock-
wise) until the engine starts to “load up” or fire un-
evenly due to a rich mixture.
7. Set the idle mixture screw midway between the
rich and lean setting. When in doubt set the mix-
ture slightly rich rather than too lean.

3B-8 - FUEL SYSTEM 90-855906 JUNE 1997

Adjusting Idle Speed ADJUSTING FLOAT DROP
1. Holding carburetor upright, bend tab (b) until
NOTE: Idle should be 850
50 RPM in gear. there is 5/16 in. (7.9 mm).
1. Shift into gear.
2. Adjust idle stop screw to proper idle rpm.

FUEL BOWL INSTALLATION

1. Install fuel bowl as shown for proper float opera-
tion.

a
a - Idle Stop Screw
NOTE: After idle speed is set, the index mark on the
throttle cam may not align with the pickup roller. This
is normal.

Carburetor Float Adjustment

55116
ADJUSTING FLOAT HEIGHT
1. Bend inlet needle tab (a) on float until float sits
parallel (horizontal) to body.

High Altitude Jet Chart

ENGINE OPER- MAIN FUEL JET SIZE
ATING ALTI-
9.9 15
TUDE
SEA LEV- .049 .070
EL-2500 ft.
2500-5000 ft. .047 .068
(762-1524 m)
5000-7500 ft. .045 .066
(1524-2286 m)
7500 ft. and up .043 .064
2286 m and up)

90-855906 JUNE 1997 FUEL SYSTEM - 3B-9