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TPS Alignment

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I removed the TPS from the carb of my nephew's CRF150R when cleaning it the other weekend and want to be sure I re-installed it properly.  There was a marking on the housing and the carb, which I re-aligned, but I had to rotate the sensor first in order for the slotted shaft inside the sensor to align with the carb.  I believe it would only rotate one direction, but don't exactly recall.  Just want to be sure I didn't screw anything up (not that it ran properly to begin with).

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My CR250X Service Manual has a range of resistance values that are used to align the TPS, so I suspect similar for your engine.

Maybe someone with a 150R Service Manual can provide more info.


on edit: the TPS is a resistor with a brush, the brush is connected to the throttle wheel and changes position on the resistor as the throttle is operated.

The ECU measures the resistance between one end of the resistor and the brush and uses that to determine throttle position.  The ECU then modifies ignition timing based on throttle position. 


The following example is based on the CRF250X Service Manual:


Measure the resistance between Blue and Black wires at the connector. Should be in the range of 4-6kΩ.

Calculate range of sensor resistance at idle speed using the above results:

 R x 0.13 = R1

 R x 0.15 = R2

The resistance between the Yellow and Black wires should be between R1 and R2 with the throttle at idle.


On my X; R=4.57kΩ

R1 & R2 calculated to 594Ω & 686Ω

My sensor resistance at idle is set at 650Ω

Edited by Chuck.
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This is one of the things that I don't care for on an off-road bike.  Having a sensor fail on an MX track is no big deal as you are close to help and a fix.  Having a sensor fail on a woods bike many miles from help and a fix is an uncomfortable thought.


I agree, and I consider the issue in risk assessment terms; e.g. how disabling will a failure be, what is the failure rate, what  mitigating steps are available.  

If my bike seizes hard or throws a rod the bike is not ridable, but in 40+ years of riding that has never happened to me.

I quit packing spare levers after installing "bark busters".

If I smack the waterpump on a rock and break it the bike is not ridable, to me a bigger risk than the two previous ones.

Same for a broken radiator although I think I could reroute hoses for only one radiator, but then I would need water.

I believe a non EFI engines with TPS  will run without the TPS but with less than optimum ignition timing. 

I don't know for sure but I suspect a failed TPS on an injected bike would probably not run, I also don't know the failure rate for TPS units.


That is probably why you, I, and a lot of others don't like using high tech like water cooling and EFI for offroad riding, and certainly my concern when planning a trip deep into the backcountry or mountains because I hate hiking in riding boots.  Over the years the low tech air cooled Honda XRs have proven to me to be the most reliable bikes for trail riding.

Have said that I know a lot of riders who take their high tech bikes deep into the backcountry and mountains and do not have problems. I have a friend with a water cooled EFI bike who has ridden it almost every week since 05 with no problems.

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