Motronic Running A Bit Rich

[The Mighty Gryphon]

Checked the plugs on my Motronic equipped '92 K100RS 4V and they are a bit black and sooty.

Air filter is less than one year old with 6,000 miles, temperature sensor is good, engine runs very smooth and strong, but does use a bit of oil(about 1 qt/800 mi).

I understand that on these systems, the Throttle Position Sensor is a linear device that indicates throttle opening amount and thus determines the amount of fuel delivered by the injectors.  I set it last winter per the specification of .375V at closed throttle, and as far as I know it has not changed.  The system on my bike does not have an O2 sensor and runs the non-catalytic Motronic control unit.

My question to the brain trust is whether I can lean out the mixture slightly with a different setting.  Has anyone tried this in the past?  Does it work or do I need to do something else to correct the mixture. 

The bike has 116,000 miles, and I suspect the injectors are worn a bit and flowing more fuel that when new.  Don't want to spend money on new ones if I can adjust the Motronic.

[kennybobby]

What sort of fuel mileage do you get?

The dark plugs could be from the oil consumption.

Only way to really know if you are running rich is to use an exhaust gas analyzer.

On the automotive motronic units there is an 8-position Fuel Quality Switch which can adjust the ignition timing +/- 3 degrees and also richen/lean out the mixture/fuel injection slightly.  That same feature may be present on the motorsickles but i don't have one handy to inspect.

i doubt the TPS voltage adjustment would have much effect on mixture, but again an EGA is needed to determine this.

[The Mighty Gryphon]

Getting between 45 and 47 mpg.   My reasoning is that if the throttle position sensor gives an air volume input I could use it to make the Motronic put less fuel into the mixture.

Bike had exhaust changed to Remus back in the '90's after cracking three headers.  Remus had no O2 sensor, so the Motronic was changed to a non-catalytic model. 

I agree that the oil may be the source of the soot, but at a mix of less than 65:1 it is in the range of two stroke mixes which can be tuned to run clean plugs. I just want to adjust the mixture to compensate for the extra carbon the oil is adding.  With a carburetor I could rejet, I am just looking for an easy way to clean things up a little.

It's not a major problem as the bike runs beautifully, it's just that being super anal about things like this, these plugs are driving me crazy.

[Laitch]

It's not a major problem as the bike runs beautifully, . . .

If that's the case, as long as the plugs look like they do, life is good. Anal preoccupation can be displaced by frugality, Vipassana meditation or spark plug type–swapping.. :giggles

[zipster68]

What kind of oil?  Dino oil burns, synthetic has a much higher flash point than dino.  Maybe a hotter plug?

If that's the case, as long as the plugs look like they do, life is good. Anal preoccupation can be displaced by frugality, Vipassana meditation or spark plug type–swapping.. :giggles

[The Mighty Gryphon]

Laitch, Zipster, I'm considering going to a hotter plug, but would rather stay with the heat range Motorrad specs out.  It is possible that I need to go a bit hotter because the synthetic oil the engine is using needs a higher temperature to completely burn off.  I suppose that hotter plugs wouldn't be a bad thing to try, I would just need to keep a close eye(ear?) on possible preignition.

[zipster68]

Would be interesting to run dino for one oil change and see if the soot abates. 

[The Mighty Gryphon]

Zipster, that might be a good idea, too.  With the engine's oil consumption(approx. 1 qt every 2 weeks) using dino would save me some cash over the course of the season.  The more I think about it the more it looks like I'll be going with 15w40 diesel engine oil and one step hotter on the plugs.  Being so late in the season, I won't have any feedback on this until spring.

[Areshuan]

I am bringing this post to life.
What were your findings  using dino, hot plugs etc after 4 years?
I have the same bike as yours with no O2 sensor and  pretty sure the potentiometer  that enriches the mixture is broken

[The Mighty Gryphon]

As luck would have it, almost exactly a year later that bike was totaled by a woman hitting me from behind.  I no longer have it.

I didn't go to hotter spark plugs or get into any significant mixture adjustments.  My thinking was that the soot was probably from the oil the engine was burning.  I ran the following year with a half quart of Marvel Mystery Oil in the engine oil with 15w40 Shell Rotella T6 synthetic.  It seems the Marvel oil loosened up the piston rings and oil consumption dropped from a quart every 600 miles to one quart every 1200-1300 miles.  It took about 2000 miles to get them loosened up.  After the accident I checked the plugs during the rebuild and they were still pretty dark, but not as sooty as they were before the Marvel oil treatment. 

I have noticed that my other bikes also have dark plugs, but I'm beginning to think it's the result of letting them idle from time to time in the winter when I'm not riding them.  I like to idle them until they warm up to circulate the oil and coolant, and charge the battery.  BMW says to start and ride away, and not to let the engine idle excessively.  I think this is because it makes the engine warm up slower so it runs on the rich starting mixture longer, putting more soot on the plugs.  Bottom line, I suspect it is my idling during storage that is causing some darkening of the plugs.   

hope this helps.

[Areshuan]

It Helps a lot !. Thanks Gryphon. I follow  must of your posts. They are very clear and insightful.   To bad you  dint have the k1100 any more.
Mine has only 36.000 Mks  but it was unused fro 17  years. Little by little is running better and stronger but i am still learning  about these machines.    I drained the 17 year old oil  and put some 10w-30  and took her for an spin for 20 mks  or so . And drained that oil. Then  use 20w-50  and new  BMW oil filter ( 50 dollars here in Ecuador)  . Rode it  for  1500 mks  more or less.  I was consuming lots of oil and the spark plugs where not only black and with soot but some oily. So i am thinking the rubber seals  are not good, Others suggested to used some high detergent diesel oil thinking the rings were not opening fully after 17 years.  SO after 1500 mks i kept the filter and put some 15w-40 diesel oil.   Rode it for 600 mks  and drained that oil.  Totally filthy . I put some new fresh 20w-50 and new filter. But i think i will go with Shell Rimula ( similar to Rotella not find her)  and i will have to smuggle some MMO   ( not found here either )
I also change spark plugs to NGK  and one of them a point hotter  and it is oaring burning the soot.
Really hope it works . Thanks for the reply !!