Engine rpm must be checked with an accurate tachometer.
Low Idle Adjustment
NOTE: The correct Low Idle rpm is given in the TMI (Technical Marketing Information) or Fuel Setting And Related Information Fiche.
Start the engine and run until the temperature of normal operation is reached. Check low idle rpm with no load on the engine. If an adjustment is necessary, use the procedure that follows:
Adjustment Of Low Idle RPM
(1) Adjustment bolt for low idle. (2) Locknut.
Adjustment Of Low Idle RPM
(1) Adjustment bolt for low idle. (2) Locknut. (3) Cover.
To adjust the Low Idle rpm, start the engine and run with the governor in the low idle position. Loosen locknut (2) for adjustment bolt for low idle (1). Turn the low idle screw to get the correct low idle rpm. Increase engine speed and return to low idle and check low idle speed again. Tighten the locknut.
Checking Set Point (Balance Point)
9U7400 Multitach Group
The 9U7400 Multitach Group is used to check the set point. Refer to Operator’s Manual, NEHS0605, for the operating instructions for this tool.
The engine set point is an adjusted specification and is important to the correct operation of the engine. High idle rpm is NOT an adjusted specification. Set point (formerly balance point) is full load rpm plus an additional 20 rpm. Set point is the rpm at which the fuel setting adjustment screw and stop or first torque spring just start to make contact. At this rpm, the fuel setting adjustment screw and stop or first torque spring still have movement between them. When additional load is put on the engine, the fuel setting adjustment screw and stop or first torque spring will become stable against each other. Set point is controlled by the fuel setting and the high idle adjustment screw.
There is a new and more accurate method for checking the “set point”, formerly called the balance point, of the engine. If the tools for the new method are not available, there is an alternate method for checking the “set point”.
If the set point is correct and the high idle speed is within specifications, the fuel system operation of the engine is correct. The set point for the engine is:
A. At 20 rpm greater than full load speed.
B. The rpm where the fuel setting adjustment screw and stop or first torque spring just make contact.
Use the procedure that follows to check the set point. Make reference to Techniques For Loading Engines in Special Instruction, SEHS7050.
(4) Brass terminal screw.
1. Connect a tachometer which has good accuracy to the tachometer drive.
2. Connect the clip end of the 8T0500 Circuit Tester to the brass terminal screw (4) on the governor housing. Connect the other end of the tester to a place on the fuel system which is a good ground connection.
3. Start the engine.
4. With the engine at normal conditions for operation, run the engine at high idle.
5. Make a record of the speed of the engine at high idle.
6. Add load on the engine slowly until the circuit tester light just comes on (minimum light output). This is the set point.
7. Make a record of the speed (rpm) at the set point.
8. Repeat Step 6 several times to make sure that the reading is correct.
9. Stop the engine. Make a comparison of the records from Steps 5 and 7 with the information from the Engine Information Plate. If the Engine Information Plate is not available see the TMI (Technical Marketing Information) and Fuel Setting And Related Information Fiche. The tolerance for the set point is ± 10 rpm. The tolerance for the high idle rpm is ± 50 rpm. If the readings from Steps 5 and 7 are within the tolerance, no adjustment is needed.
NOTE: It is possible in some applications that the high idle rpm will be less than the lower limit. This can be caused by high parasitic loads such as hydraulic pumps, compressors, etc.
Adjusting Set Point (Balance Point)
1. If the set point and the high idle rpm are within tolerance, no adjustment is to be made.
Adjustment of Set Point
(5) Adjustment screw. (6) Locknut.
2. If the set point rpm is not correct, remove cover (3) and loosen locknut (6). Turn adjustment screw (5) to adjust the set point to the mid point of the tolerance.
3. When the set point is correct, check the high idle rpm. The high idle rpm must not be more than the high limit of the tolerance.
If the high idle rpm is more than the high limit of the tolerance, check the governor spring and flyweights. If the high idle rpm is less than the low limit of the tolerance, check for excess parasitic loads and then the governor spring and flyweights.