K75 running worse when warm but fan kicks on fine.

[X5acob]

I'm trying to diagnose poorly running k75. Gets horrible gas mileage (under 25mpg) runs worse when warm. It's rideable but you can feel it skip when coasting or cruising under light throttle. Acts like maybe a bad temp sensor, but the fan kicks on and off just fine. Since I got it last year I've replaced the injectors, plugs, fuel pump and fuel filter. I've evened the vacuum as best I could with a cheap 4 gauge carb balancer.
Couldn't find any air leaks using the "spray carb cleaner near potential leaks and listen for surge" method. I've unplugged the tps without any change. Pushed green start button while running idle drops a little. Could the temp sensor still be bad even if it works to turn on the fan?

[frankenduck]

When's the last time the fuel filter was inspected/changed?

NAPA 3032 is readily available at only $6-7 and works fine compared to the $44 OEM fuel filter.

[X5acob]

Yea, changed it last year. And it's running rich. I don't think a clogged fuel filter is my issue.

[Duckbubbles]

Years ago I had the water temp sensor on my K100 fail by telling the computer that it was super cold and needed more fuel to run.  It would spit raw fuel out of the exhaust pipe.

Frank

[frankenduck]

You can check the temp sensor resistance at L-Jetronic Pin 10 as described here:

http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/tempsensor/tempsensor.htm

[Laitch]

Could the temp sensor still be bad even if it works to turn on the fan?

It could be half-bad because there are two separate circuits in the sensor responding to coolant temperature—one signal goes to the injection control unit and the other to the temperature relay which controls the fan. One circuit could break down while the other could still function. Look at the attached diagram.

[X5acob]

Thanks for the heads up! Ordered a new Temps sensor from EME. Hopefully that's the ticket. In the meantime I gave it a much needed detail.

20220522_161250~2.jpg (147.71 kB . 768x576 - viewed 317 times)

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A few changes since I last posed pictures of the bike. New rear shock, bags and mounts, RT bars, new grips, and extra lights. And just put on some new Pirelli Sport Demons.

[frankenduck]

How to replace the  temp sensor:
http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/airtemp/airtemp.htm

[X5acob]

I replaced the temp sensor, bit doesn't seam to have made a difference. Just running very uneven when hot. Definitely runs better before it gets to temp. And maybe even worse on a hot day. Could it be the Hal sensor?  Went for a 3 hr ride yesterday because I'm a glutton for punishment. Going slow through downtown sections I felt like was riding a Harley with how skipy and uneven it was.

[frankenduck]

Are you sure that the spark plug leads leads are FIRMLY installed on the spark plugs? Those often need an extra nudge to get well-seated on the plugs.

When coils start to fail the bike will run rough when heated up but coil failures on K75s are rare.

Flaky HES symptom is usually that the bike dies completely until it cools down.

How many miles on it?

[X5acob]

plug wires are fully seated. Had 16k on a dead cluster when I got it.

[Laitch]

I replaced the temp sensor, bit doesn't seam to have made a difference.

What is the EME part number of the sensor you purchased? Using the troubleshooting guide, test the socket of pin #10 of the fuel injection control unit under the seat after the moto is warmed up, then tell us what its value is. You'll find diagrams, explanations, and coolant temperature sensor resistance/temperature values starting on page #21 in the troubleshooting guide here. The link is at the bottom of the first post. Scroll down to find it.


Check the vane in the air flow sensor to verify that it moves freely and check its electrical connector to verify that it is connected firmly. It's attached to the air box. Its description starts on page #10 of the guide already cited.


Try to restrain yourself from buying a remedy before using testing to verify that it is needed, but we all understand isn't easy with the Web beckoning us 24/7 with promises of fulfillment. 

[X5acob]

Sensor k197 seems to test good. I notice that when I press the start button  when at idle the rpm drops, and no amount of adjustment to the flow screw can I get it to rise when hitting the start button.