Motronic Running Rich

[The Mighty Gryphon]

My '92 K100RS is running a little rich.  Plugs have dry, fluffy black carbon deposits and when the throttle is goosed I get a quick burst of black smoke.   Fuel efficiency is running about 45mpg.   Aside from a barely noticeable stumble around 2000 to 2500rpm the engine runs well and pulls strong through the gears.

Bike has a motronic system.  As far as I can tell it is set up to run without the catalytic unit and the O2 sensor.  Bike has had a history of broken exhaust welds, and now has a standard K100 exhaust system. 

I understand that the mixture is controlled by three inputs, engine temp, air temp, and throttle position.  I have tested the engine temperature sensor and it looks like it is working properly.  I have also set the throttle position sensor. 

I have a few questions.  First, how does one check the air temperature sensor? 

How does one adjust the mixture pot on the side of the relay box?  Does it control the mixture at anything above a closed throttle?  Which way would I turn it to lean out the mixture?

Is there anything else that controls the mixture? 

[Martin]

 Gryph I couldn't get anyone to adjust my mixture correctly so a ended up buying a Gunson gas tester from the UK, looks a bit cheap but has worked well for last 10 yrs.
If you are idling at 1000 rpm and press the starter motor button the bike does a self check the idle should stay the same or only rise a little. If you don't have access to a gas analyzer you can also check by doing the lean drop method it is posted.
Regards Martin.

[The Mighty Gryphon]

Yeah, I need to find that lean drop method write up.  Used to set up all my enduro bikes that way.  Back then it was carburetors and we called it "lean best idle".  Not sure if it will help that much, as the bike seems to be rich at all throttle settings.

Anyone have a link to a test for the air temperature sensor?

[Martin]

Gryph have you tried pushing the starter button it must be at 1000rpm to do so, otherwise starter will engage, it will give you an idea. You can test the temperature switch, all you need is a thermometer and a multimeter. RBM has posted a chart under RE Coolant Temp Sensor Values.
Regards Martin

[The Mighty Gryphon]

Martin, Tested the coolant temp sensor in hot water with a dvm when the head was off.  Tested ok.  What puzzles me is how to test the air temp sensor that I understand determines the air flow in the Motronic system.

[TimTyler]

You can adjust the fuel mixture using the hex screw in the front top right corner of the air box. AFAIK that's the only place to adjust the mixture. You'll need to remove the rubber plug over the hole, then stick a hex/allen key down into the hole. The screw adjusts the quantity of air that is allowed to leak into the air flow meter. It's an entirely low-tech adjustment, not some electronic or complex mechanical adjustment.

To enrich the mixture, tighten the screw which reduces the amount of air leaked in. To lean the mixture, add more air by unscrewing the screw.

If you don't have access to an exhaust analyzer (which will allow you to see the mixture value in real time) I recommend you note the position of your wrench in the screw before adjusting, and then turn it one half turn. Write down the direction you turned the screw and then check your plugs in a few hundred miles (or more?). Don't try to commit your adjustment solely to memory or you'll be questioning yourself the next time you choose to adjust.

DynoTune guys have exhaust analyzers.

[Martin]

Gryph seeing as you have a bit of a brick KOOLlection and if you have a few other Motobricker mates locally. It might be worth while forming a pool and getting a Gunson Gas Analyzer. It has been one of my better purchases. I don't know how much they are in the US they were the cheapest working ones when I got mine.
I am wiring in another relay tomorrow as well as dropping off bits for painting.
Regards Martin.

[Inge K.]

You can adjust the fuel mixture using the hex screw in the front top right corner of the air box. AFAIK that's the only place to adjust the mixture. You'll need to remove the rubber plug over the hole, then stick a hex/allen key down into the hole. The screw adjusts the quantity of air that is allowed to leak into the air flow meter. It's an entirely low-tech adjustment, not some electronic or complex mechanical adjustment.

That's valid on Jetronic equipped models, Motronic models haven't got a AFM. (using the TPS to calculate)
Non cat Motronics have a variable resistor in front of the relay box to adjust mix (at idle and a hair above).

[The Mighty Gryphon]

Inge, I see that resistor and have been wondering how to go about adjusting it.  I suppose plug readings at idle would do it.  Which way do I turn to lean the mixture? 

Is there a procedure for checking the sensor that is in the top of the airbox?  The one that has the connector just in front of the relay box on the right hand side?

[TimTyler]

...Motronic models haven't got a AFM. ...

Doh!  :mbird Thanks, Inge.

[Inge K.]

Inge, I see that resistor and have been wondering how to go about adjusting it.  I suppose plug readings at idle would do it.  Which way do I turn to lean the mixture?

First a correction....the Co pot meter will affect the mix throughout the whole rpm range.
Turn it clockwise to weaken the mixture...it's a sliding contact shoe connected to a threaded bar,
be careful to turn it to far in either end...as it is posibble to "derail" it...should be around 500 ohm i center pos.
Also check the contacts in the connector for corrosion........correct Co is 1.5-2.0%.

Is there a procedure for checking the sensor that is in the top of the airbox?  The one that has the connector just in front of the relay box on the right hand side?

Never had any trouble with the air temp sensors, so I have no specs.
In the troubleshooting guide at the K100forum it's a table for the one on the 2V's, don't know if these values
is the same on a 4V.....but it could be a good idea to compare them.

[rbm]

Richness could point to failed or failing injectors.  I helped Larry Romestant troubleshoot running problems on his K1100 Beast.  His was running so rich it belched black smoke, wouldn't idle properly and backfired.  Ended up being failed injectors.

[The Mighty Gryphon]

Inge, Rob, thanks for the replies.  Will try the CO pot first.  Will try some adjustments followed by idle plug readings to see if I can get any improvement.  I should be able to do that without actually taking the bike out on the icy roads around here.

Rob, with 110,000 miles, I suppose the injectors could be failing.  Do you think it's a function of the pintle sticking open, or is the orifice wearing?  I still have the fairing off and can mess with them.  I also have some spare injectors I got on a spare K75 engine I just bought.  Am tempted to swap one of them in to see what effect it may have on the plug readings. 

Garage is at 15F so it will be a few days before I get out there again.

Thanks again, guys.  BTW, Rob, when do you think you want to get together with some of us for lunch and a chat?  Bocutter Ed has already offered his shop for a meeting place and he says there is a F&C place near by. 

[rbm]

Do you think it's a function of the pintle sticking open, or is the orifice wearing? 

It's a function of the valve in the injector staying open.  Then fuel doesn't get turned off immediately and rich mixture results. Do the swap with the K75 injectors.  Meanwhile get the others cleaned and balanced at Mr. Injector.  Always good to get a spare set from ebay to have at the ready.

Thanks again, guys.  BTW, Rob, when do you think you want to get together with some of us for lunch and a chat?  Bocutter Ed has already offered his shop for a meeting place and he says there is a F&C place near by.

I'll get in touch with Ed and we'll send out an invite.  I'll probably have time towards late Jan. / early Feb.

[The Mighty Gryphon]

Rob, I'll see if I can get hold of Kris.  Every day is Saturday for me so whenever it works for you guys is good for me.

Seems there are some new folks here from the GTA and Simcoe region.  I have posted a notice in the meeting board, so I guess we are committed now.