Carburetor, fuel pump, throttle linkage,  M110

Testing and adjusting TN choke for function



07.2—130 Testing and adjusting TN choke for function


Testing and adjusting values


TN control piston overlap at + 85 °C coolant temperature
0.8-1.0 mm


TN control window opening at + 20 °C
approx. 2.5 mm


Special tool


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000 589 40 37 00


Conventional tool


Combined slide and depth gauge


Testing, adjusting

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1    Run engine to operating temperature (coolant thermostat opened (approx. 85 °C).
2   After loosening the two fastening screws (arrows) pull out TN choke with water hoses connected.
TN choke version 2 with enlarged expansion element and housing


3 Test and adjust TN control piston position. For this purpose, after pulling out TN choke, immediately measure dimension “X” from face up to upper edge of control window directly adjacent to web.
Measuring is required immediately because upon cooling down the expansion element will respond and cause control piston to move to another position.
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Measuring dimension “X’


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4 Then measure dimension “Y” from face up to edge of control piston.
Dimension “Y” should be 0.8—1.0 mm smaller than dimension “X”, so that the control piston will close control window with overlap.
TN control piston overlap: at + 85 °C coolant tem­perature 0.8—1.0 mm.
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Measuring dimension “Y”


5 Adjust TN control piston position by means of adjusting screw.
Screwing out = reducing overlap Screwing in = increasing overlap
Note: At + 20 °C temperature of TN choke, the TN control window should be open by approx. 2.5 mm. Each 10 °C of temperature change will cause control piston to travel approx. 0.5 mm, i.e. at approx. 70 °C coolant temperature the control window is just closed. At approx. 0 °C the control window is wide open.
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6   Pinch coolant hoses on TN choke and pull off.
7    Let TN choke cool down below + 20 °C (e.g. tap water) and then measure TN control window opening “a”
Nominal value: min. 2.5 mm.
(If control window opening is essentially less, replace TN choke).
8    Reinstall TN choke.
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