The Throttle Position Sensor (TPS) determines the amount of throttle being used for input to the ignition module. Correct orientation of this sensor is essential for proper operation of the engine.

To test if the throttle position sensor mount angle is correct:

1. Remove the Seat
2. Remove the Fuel Tank Hold Down Bolt
3. Prop Up the Front of the Tank
4. Turn Fuel Petcock to OFF for Safety
5. Turn the Ignition Switch to ON
6. Disconnect the Throttle Position Sensor Coupler
7. Reconnect the Throttle Position Sensor Coupler. After reconnecting the Throttle Position Sensor Coupler, the tachometer switches to the Throttle Position Sensor Adjustment Mode
8. Read the Tachometer RPM

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If the tachometer reading is:

• 0 - the Throttle Position Sensor Angle is Too Small
• 5,000 - the Throttle Position Sensor Angle is Correct
• 10,000 - Throttle Position Sensor Angle is Too Large

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To adjust the Throttle Position Sensor Angle:

• Loosen the throttle Position Sensor Screws, T-20 security torx screws. Vermont American part# 15354 about $4.
• Manually adjust the angle of the sensor until the tachometer reading is 5,000 rpm. If the 5,000 reading is not achievable try turning the idle speed adjustment screw.
• Tighten the Throttle Position Sensor screws

The tach will read the correct 5,000 rpm value within a range of adjustment. There have been reports of improved engine starting with the sensor set at the greatest counterclockwise angle that still registers a 5,000 rpm reading. Other reports indicate being able to reduce vibrations with the TPS adjusted within the range.

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To exit the Throttle Position Sensor Adjustment Mode on the Tachometer, start the engine or turn the ignition switch to OFF. When lowering tank remember to switch fuel petcock back to ON first. Make sure the fuel tank hold down bolt is properly torqued to 10 Nm, 7.2 lb-ft.

Another Excellent Article on Throttle Position Sensor Adjustment can be Found Here

Addendum:

From Ivan, an alternate approach to TPS adjustment.

1. Warm up the engine completely.
2. Loosen the TPS screws so that it can easily be moved.
3. Start engine and set idle speed to 3800 rpm.
4. Move throttle sensor to get highest engine speed.
5. Tighten screws (make sure that speed does not change during tightening).
6. Lower idle speed to 1200 - 1300 rpm.