The TPS adaptor on the carburetor is responsible for reporting the position of your throttle to the ignition (ignitor). The ignition uses this information to adjust the timing curve on the bike to match driving conditions.

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We have seen some broken TPS's that failed to do so, and the bikes they came in on were somewhat sluggish to drive. To assist those who may need to check, adjust, or replace their TPS adaptors we put together this brief paraphrase of the instructions in the service manual.

If you are not comfortable working with a Multimeter, we suggest getting some assistance from someone who is.

Check your TPS:
  • With the TPS cable disconnected from the bike’s harness, you’ll see that the wires from the TPS are Blue, Yellow, and Black. Using an Ohmmeter (the digital type is best), measure the resistance between the terminals for the Blue and Black wires. It should be between 4k ~ 6k Ohm at 68-degrees F. Temperature IS a factor, so you’ll find it will vary some with different temps. Throttle position is NOT a factor in this measurement.
  • Measure the resistance between the Yellow and Black terminals, with the throttle closed. If it does not fall within the desired range, then by loosening the M4 screws holding the TPS to the bracket, you can rotate the TPS until it shows the correct reading on the Ohmmeter. With the right setting established, retighten the screws. So far, I've found that every TPS I've installed has needed a setting of 650 to 675-Ohm. If you measure the resistance between the Yellow and Black terminals while opening the throttle from idle to full open, you should see a progressive change from the set point to a maximum between 4k ~ 6k-Ohm.

Not all digital ohmmeters are setup the same. Some have a multiplier on the LCD for each scale (X10, X100, X1K, and X10K), but yours may have range limits that just indicate the highest limit of each setting on the dial. With that type of ohmmeter you'd use the 10-K or 20-K scale (whichever it comes with) while reading the blue & black wires (which just means that 10,000 or 20,000 Ohms is that scale's greatest resolution). The reading taken from the blue & black wires is the maximum resistance of the TPS and isn't effected by throttle position. When you measure the resistance between the blue and black wires you should get something in the neighborhood of 5,000 Ohms (give or take about 500). Multiply that number times the standard of .13 to .15 (I just use .14) and the result is the resistance to set the TPS position to, while reading the yellow and black wires. With ohmmeters that have range limits, you'd use the 1K or 2K scale (whichever it has) to set it while connected to the yellow and black wires. The yellow and black wires show the variable resistance of the TPS depending on throttle position and what you're doing is setting the nominal resistances at idle.

Once it's set, if you open the throttle you'll see the resistance across those wires climb between 4,000 to 6,000 Ohms. When you drop the throttle back to idle, it should return to the previously set reading (plus or minus 25 Ohms). It'll vary some, so don't sweat it if it doesn't return to exactly what you set it to.