Why is my bike running rich and stinking the garage out?!

I love riding this bike, but why does it smell so strongly of exhaust fumes?

It's a 1998 R1100GS with about 84,000 miles. I've owned it for 12 months and it's really well maintained. The bike goes really well... but it stinks! It's most noticeable when I pull up at junctions, etc. The end of the exhaust, and back of numberplate, is always black and sooty. It's been like this since I bought the bike and although it runs great, I would like to get rid of the smell... my garage stinks of it!

All oils are fresh
Clean air filter
Recent plugs
Valve clearances are perfect
TBS was 0.28V I adjusted to 0.36V but it's made no difference
Throttle body balance is perfect
All cables replaced. Throttle body cables are set up to perfection (Problem existed before I changed these anyway)
Bike has Lennies sprockets fitted
Bike had Gemini John chip (for sprockets) fitted. I changed back to standard... no difference
Standard exhausts.

The bike starts well, idles perfectly and pulls well. I get "about" 10 miles per litre.
The bike occasionally backfires when changing down a gear. (maybe once for every 100 down shifts. Manifests as a pop from the silencer). I assume this is unburnt fuel that is being ignited in the exhaust pipe?

What do I do next?!

Thanks in advance.

Suspect either your lambda probe, or CO potentiometer…..depending on which is fitted.

I suspect it is possible that a late 97 on Build will have a Lamda

Simplest test is to unplug the Lamda plug and test ride it

Also the TPS tells the ECU what the throttle angle is and then the ECU correlates the intake air temp Engine oil temp and the throttle angle to then change the injection time to spill Less or more fuel in

So you could have a dodgy TPS going out of whack once you move into the mid range or its track

AND finally the Fuel pressure regulator If the return pipe is restricted or squashed somewhere then the excess fuel cannot return to the tank so the fuel rail is maxed out at pump pressure rather than pressure relief valve pressure

After a proper ride, take out the plugs and take a look at them. They should be a light brown/tan colour. If they are black and sooty then the engine is running too rich.

I had a 94, 95 X2 and a 99 and they all had co2 pots... Had one replaced for the symptoms you describe... Also if the bike is running with no cat code plug it will run rich... At 10 miles per litre you are doing ok though for consumption... The other thing it that if you have been running late carb Japanese bikes or injected lambda controlled bikes you will notice the stink even more so... It has been a shock to me to have with and without in the garage and notice the shite we were living with before... My experience with BMW plug chops on any injector era bike it that they always look lean even when normal running ..

Following the thread as my 1200GSA has the same issue. Most of the stink is being decat, but it developed a very strong petrol smell in the last few years (when parked) and I cannot see no leaks.

I had a petrol smell from my year 2000 1150 GS that turned out to be rotten seals around the fuel cap, rain water pooled there and slowly soaked in causing a small pool of water in the bottom of the tank which caused rust... tank off, sanded back the tank, filler over the area, rattle can painted and a new filler cap... no smell at all now... Good for another 130k....

Thanks for the advice and suggestions.
So...
Fuel return is fine,
TPS looks good,
No lambda probe,
Beige coding plug in place,
And I've located the CO pot*


*I cocked up at this point. Thought I'd wind it in whilst counting turns. Didn't realise it was a never ending job! Managed to lose track of where I was up to... So no idea now
Guess I need to find a CO tester in order to set it up? Anyone near Stockport have one I could use?

Cheers

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