M620 running ric

[pooh]

Hi folks
I've got a problem with the wife's 2004 620, it runs really rich at low rpm and pops back into the air box. The exhaust tips are thick soot.
So far I've changed the following air filter, injectors, throttle bodies, temp sensor, ignition coils, plugs.

I've also checked valve clearances, cam timing etc does anybody have any ideas as she's getting fed up of not being able to ride it. It can be ridden but can catch you out in corners when the engine splutters and it's also dodgy when pulling out of junctions.

Any ideas will be gratefully accepted.

Thanks
Ian