Testing; Service; Carburetor Pre-Set And Adjustment - Tecumseh TM SERIES Technician's Handbook

TESTING

1. After 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 and removing the spark plug. Install a Tecumseh Spark Plug Tester (part # 670366)
and check for spark. If the spark is bright blue and fires every revolution, proceed to step # 2. If no spark, weak spark,
or intermittent spark, see Chapter 6 "Ignition" under "Troubleshooting".
2. Remove the spark plug and visually check the removed spark plug for a wet condition indicating the presence of
fuel mixture in the cylinder.
3. If the spark plug is dry, check for restrictions in the fuel system before the carburetor. If the spark plug is wet,
continue with step #7. Check the fuel cap vent, the cap must allow air to be blown through it when testing. Using a
proper draining receptacle, remove the fuel line from the carburetor inlet fitting (TC Type I) or fuel tank (TC Type II/
TM) and pull off the fuel line. Examine the fuel flow and fuel condition. Improper fuel flow indicates the fuel, fuel line,
filter, or tank require cleaning or replacement.
4. Visually inspect the choke shutter for complete closing or check to see fuel flowing from the main nozzle during
priming. Remove the air cleaner element or air cleaner assembly to provide access for visual inspection.
5. If the fuel flow to the carburetor is adequate and no fuel flows out the main nozzle during priming or choking, the
carburetor will require service. Consult the Troubleshooting Carburetion Chart for possible causes for the lack of
fuel.
6. Check the compression release on TM engines. Low compression, no fuel present on the spark plug, adequate fuel
flow and a known good functional carburetor indicates an internal engine problem exists. See Chapter 7 under
"Troubleshooting".
7. Check the engine compression using compression tester (part # 670358) and follow the tester's recommended
procedure. Low compression, no fuel present on the spark plug, adequate fuel flow and a known good functional
carburetor indicates an internal engine problem exists. See Chapter 7 under "Troubleshooting".

SERVICE

CARBURETOR PRE-SET AND ADJUSTMENT

The Walbro, Tillotson and Tecumseh carburetors used on
TC engines have non-adjustable main mixture jets. Only
the idle mixture may be adjustable by turning the idle
mixture screw. Use the following procedure to pre-set the
idle mixture screw. Turn the idle mixture screw
(clockwise) finger tight to the closed position, then turn the
screw counterclockwise to obtain the proper preset (diag.
3-10).
Walbro model WTA, WT
Tillotson model HU
Tecumseh model
Final Idle Mixture Adjustment
Start the engine and allow it to reach normal operating
temperature (after 3-5 minutes). As the speed control is
set at the idle position, turn the idle mixture screw slowly
clockwise until the engine R.P.M. just starts to decrease.
Stop and note this screw position. Turn the idle mixture
screw slowly counterclockwise. The engine will increase
R.P.M. Continue to slowly turn the screw until the engine
R.P.M. starts to decrease. Note this position and turn the
mixture screw back clockwise halfway between the two
engine R.P.M. drop off positions. The idle mixture
adjustment is complete.
1 - 1 1/8 turns
1 1/4 - 1 3/8 turns
Fixed
Idle Mixture Screw
3-10
19