Testing - Tecumseh V-twin Technician's Handbook

Main Nozzle Air Bleed: Air is bled into the main nozzle
through the main nozzle air bleed passage located in
the 6 o'clock position of the carburetor's choke end. (Illust.
3-6) This passage allows air to mix with the fuel traveling
up the main nozzle creating a pre-atomized mixture. The
fuel is then released into the venturi from the nozzle tip.
Atomization occurs as the fuel mixture contacts the fast
moving air stream in the venturi and flows into the intake
of the engine.
Low Speed Idle Air Bleed: The low speed circuit of the
carburetor has an idle air bleed passage which performs
the same function as the high-speed air bleed. It pre-
mixes fuel and air prior to entering the throat of the
carburetor. This passage is located in the idle mixing
well (Illust. 3-7)
LOW SPEED
IDLE AIR BLEED
IDLE MIXING
WELL

TESTING

1. Should repeated efforts to start the engine using the
procedure listed in the operator's manual fail, check
for spark by removing the high-tension lead. Install
an ignition tester and check for spark. If the spark is
bright blue and consistent, proceed to step 2. If no
or irregular spark see Chapter 6 under "Testing".
CAUTION: KEEP ALL COMBUSTIVE SOURCES
AWAY. AVOID THE SPRAY FROM THE SPARK
PLUG HOLE WHEN CRANKING THE ENGINE
OVER AND MAKE SURE THE PLUG WIRES ARE
PROPERLY GROUNDED TO THE DEDICATED
RETAINING POSTS.
2. Remove and visually inspect the condition of each
spark plug, a wet condition indicates the presence
of gasoline in the cylinder. Although this indicates
fuel is present the fuel condition regarding its
combustibility should always be checked.
NOTE: Check plug for correct reach. (Illust. 3-8)
STANDARD
PLUG
3-6
3. If either spark plug is dry, check for restrictions in
the fuel system, which supplies that cylinder. If both
plugs are dry check the fuel supply system and
continue with step #4. If the spark plug is wet,
continue with step # 8.
4. Dry Spark Plug: Begin by checking the fuel cap for
proper atmospheric venting. With the fuel cap in place
and tightened, remove the fuel line prior to the pump
allowing fuel to flow into a proper receptacle. Allow
at least 1 gallon of fuel to flow out, noting the rate of
flow. If it remains consistent the vent is performing
properly. Re-connect the fuel line(s) to the pump.
NOTE: Today's fuels can cause many problems in
engine performance due to the fuels quality and short
shelf life. Always check fuel as a primary cause of
engine poor performance.
5. Remove the air filter, visually check the choke
3-7
shutter(s) operation for complete closure when the
throttle or independent choke control are in the full
choke position.
OHV
3-8
3-3