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Hello, This is my first post here. I have posted my question in GS911 (hex code) forum, but I thought I might get more response here, so am reposting.

My 2000 K1200RS, which I have had for more than 5 years has always run rich. It also hesitates on accelerating but in general I have no problem cruising and it has all the power. I can also smell that the engine runs rich, and fuel efficiency is in low 30s.

I did lambda voltage test and there were long periods of flat voltage, so I changed the O2 sensor. I believe the problem is somewhere else, because this is not the first time I have changed the O2 sensor.

I am posting results after changing the O2 sensor. There are two graphs: First one is while idling and in the second one I tried to increase RPM to 2000 and 3000 and then released it to idle. I noticed that the O2 voltage was showing flat when it idled after revving. Can you comment on these graphs? Engine was hot (tested after a 15 mile ride) in both cases.

I am also plotting the TPS on the graph. It seems to be changing, but I notice that it doesn't follow the RPM properly.
I also have a question regarding O2 sensor itself. Can it go bad by carbon fouling from a rich engine?

I have not really checked the throttle body, air filter and everything that is inside the fairings. If I remove the fairings, I would like to do all the necessary checks and maintenance, so any recommendations will be greatly appreciated!

I have the data for both these tests, so let me know if it will be useful to plot any other variables.

PS: A correction: The blue curve in the first graph is indeed for TPS. The right side Y axis shows ignition time incorrectly (because I had it there earlier and then removed it and then forgot to change it in Kaleidagraph). Thanks
 

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hmmm 2000 k12... if that's the "old style" brick motor, I had two '85 K100s that were similar. L-Jetronic fuel injection, main control is the "barn door" AFM and the fuel pressure regulator.

Rich running is too much fuel or too little air. It can be caused by an AFM outa whack but for the moment we will assume yours is okay and you have not messed with the adjustment screw. We will also assume no restriction in the intake such as a clogged air filter (you checked, right?).

The likely cause is that the air hose from the fuel pressure regulator to the intake manifold (I think that's where it runs, it has been a while). The function of the FPR is to sense the difference between manifold and outside air pressure, and adjust the fuel pressure so the injectors are always operating across the same pressure differential. Anyway, the hose is about 1/2 inch diameter and has a kinky shape with different size ends. It can crack at the bends and then your fuel pressure is unreliable. I don't think there is a simple replacement, because of the different sized ends you have to get the factory part, but at least it's not all that expensive. Make sure you install with the correct ends in the correct positions, it's easy to mistake them b/c they are not that much different. The hose doesn't see much pressure difference so it's not required to use a hose clamp(s).

My experience with the GS-911 forum was miserable. They are only about using the tool, not actual troubleshooting. I don't go there any more.
 

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I won't comment on the graphs.Running rich/hesitations on acceleration?I have been through that!

Send your fuel injectors out for an ultrasonic cleaning/balance/spray pattern test.

Something like this:


https://www.mrinjector.us/?gclid=Cj0KCQiAm4TyBRDgARIsAOU75srx_86S6hkw8icaG0IG_rUEivbTOHU5BzwLEttL2TDMu1gJJLE-wlEaAh4ZEALw_wcB
One or more may not fully close which let more fuel in when it shouldn't.And if not atomizing the fuel correctly it won't all burn as it should and of course will run rich!
 

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And at the same time look for vacuum leaks!TBs should come off, they are well known for cracking the rubber inlet manifolds.And the plastic stubs bolted to the head are known for warping.Or even corrosion seeping between the stubs/head and attacking the o-rings mating surfaces.

Vacuum leaks usually show up as an oily residue around the leak but if behind the TBs that's pretty hard to see.And the infamously prone to splitting crankcase breather distribution hose is also behind the TBs.
 
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