Installing the Throttle Position Sensor (TPS)on SU Carbs
SU Carburetors, unlike the Zenith Stromberg carbs, have a smooth throttle shaft so they require a TPS Driver that can clamp tightly onto a smooth shaft. Pictured here is a typical SU carb showing the smooth throttle shaft (Float bowl removed)
The SU TPS has three parts, the Driver, The bead, and the Locking Nut. Beads and nuts are 5/16”tube and available at most hardware and auto parts stores. The driver assembly is a custom part only available from Patton Machine.
Install the TPS bracket under the two nuts that secure the carb to the intake manifold.
The TPS Locking Nut slips onto the throttle shaft with the smooth side toward the carb body, threaded side toward the sensor. Next the bead slips onto the shaft and should go on far enough that the throttle shaft passes all the way through the bead. Next up is the actual TPS driver. At this time, they should just be assembled finger tight.
Rotate the driver so it’s forks align with the sensor and mount the sensor using the two #8 socket head bolts with a lock and flat washer. At this time the forks of the driver will be in the sensor engaged with the sensor’s drive lugs but not locked onto the throttle shaft as yet, free to rotate.
Note if the sensor does not easily slip into the bracket’s pocket you may need to tweak the bracket to align it properly. If the sensor does not just slip into the bracket it may bind the throttle shaft and prevent the return to idle speed.
Next is to connect your laptop and open WinALDL’s DASH window providing you have already configured WinALD with your vehicle. If you have not yet configured WinALDL see: Setting up WinALDL and Creating a DATALOG file
With WinALDL running and the DASH window open, turn the key on but do not start the engine. Temporarily now using two ½” open end wrenches rotate the hex of the driver closest to the sensor until the TPS% reading in the DASH window reads between 0 and -0.3%. Now while holding the driver from turning with one wrench use the second wrench to tighten the locking nut closest to the carb body. This will crimp the bead onto the throttle shaft. Easiest if the first wrench is on the driver from the backside of the bracket and the second wrench from the near side of the bracket on the lock nut. This adjustment is temporary as anytime the idle setting changes by moving the throttle shaft the sensor output will change. Onlly after setting up the base idle to 900 rpm will the TPS setting be final.
Next up is to set the Base Idle to 900rpm see: