BMW K1100 Running Rich

[Davehsw]

Hi All,
Here I am again asking for advice. The joys of older bikes!

My 1995 BMW K1100LT is running very rich (9.5 to 10.5% CO2). When the adjuster screw is turned in either direction the CO2 goes up!

Any suggestions?

[Snowy]

Which adjuster screw are you turning? The only ones I ever touch are the air screws on all four cylinders when syncing the throttle bodies. Plus, when was the air filter last changed?

[jonnydangerous]

like Snowy says, a few checks first then dig in to see if it IS a problem (is it idling rough)....but.....this might not ba a problem, i had a gsxr 750 that ran luuuuurvly and it put the co2 meter off the scale....
some of the older bikes had very poor combustion chamber design, control over ignition timing, advance, fuel metering at idle /progression...

do you have a spec for the idle mixture for the Beemer? can you use a "colourtune" tool to check the actual mixture strength, or can you add a wide range O2 sensor to the exhaust and see the voltage? (will give you an oxygen content of the exhaust gas and the mixture strength...

if the carbs have idle jets that are too big you might be able to change them.

[Davehsw]

The bike has been serviced. I was being followed by a biker who said he could smell where I had been! Plus the consumption is awful.

The BMW manual shows a screw to the right of the throttle position sensor as the adjuster for mixture!

I put the bike on an MoT gas analyser to get the readings.

[Snowy]

Did this just start after the service then?

The spec is 1.5% +/- 0.5% CO2 so you are way off. Do you notice any difference between cold and hot running? If the air or water temperature sensors were up the creek the bike would run rich thinking its cold all the time so would start OK and then get rough.

[Davehsw]

Ever since I had the bike it ran really bad. I have replaced the water temperature sensor, the throttle position sensor and any parts where I thought air could be getting in as it idled okay, but made strange clunking noises at 2,500 rpm.

I then changed the throttle body (?) with a second hand one and the bike has run so much better since. It appears to run okay, but I have no reference as it wasn't perfect when I got it.

I thought it was okay until my follower said it was running ridiculously rich. I haven't noticed any hot or cold differences.

[Snowy]

Have the throttle butterflys been messed around with? If you look at the silver screws they have yellow paint on and are covered in a laquer. They are not supposed to be touched so if a previous owner had, they might be out of sync with each other. Did they balance them during the service?

[Davehsw]

They did balance them as they had previously been played with.

[Snowy]

According to BMW, those butterfly valves are not to be adjusted - if they are, the earths rotation will stop and hell will freeze over. They say these can only be reset at the factory. Loads of people have got into trouble adjusting these thinking thats the way to balance the throttle bodies which you only do via the brass vacume screws. However, there are guru's who have documented how they have been able to set these up successfully. Its covered extensively on the K11og site. I have never touched mine and there really should never be the need to. I don't know if that is what is causing the over fueling but it is something to consider.

The air temperature sensor is at the rear of the air box - difficult to get to but its at least worth checking that as well.

What sort of mileage are you achieving? I tend to get about 45mpg however I am riding.

[Davehsw]

39-41, but I am a very sedate rider.

[Snowy]

Well, 40mpg avg is not too bad.....your LT is heavier than my RS.

Did they change the air filter as part of the service? Its an absolute mare to do - so many don't.

The air temperature sensor could be the culprit - if thats awol it will keep the mixture rich. Worth checking.

Who did you use to set the throttle bodies up? As I said before if the butterflys have been tampered with, you will need some expert knowledge/experience to get them resynced.