As mentioned in this post [], rebuilding my Weber DMTL carburettor was one of the first things on my list of curing my misfire problems, which turned out to be a more serious blown head-gasket. Still, restoring the carb. is one of the first things the previous owner told me I should do and gave me a brand new Weber rebuild-kit with the car, so I guess it can't hurt the old girl.
This job isn't for the faint hearted though, so if you have a disposition towards botching fiddly things as I generally do, then it's probably best left to a pro - I messed up my throttle-cable and had to replace it, and fettling the throttle-spring arrangement was all but impossible to get back to how it was. It's still not right, throttle springs etc. a bit loose, but at least its running ok again.
Here's a great guide for tuning the carb. once it's rebuilt:
http://www.carburetion.com/Weber/adjust.htm**CAUTION: If you're running a Weber on an E21 then your 'Bowden' throttle-cable will likely have been cut to fit through the cable-eye on the throttle linkage. Cutting the metal end off the cable causes it to lose its tension and the strands begin to unravel immediately so be very careful when removing and fitting the cable to the carb. [especially if you need to do it more than once which broke mine], as once the cable has begun to expand inside the sheath it binds very easily and you will need a new one. These aren't in production anymore either and I got the last one from BMW Classic in Park Lane, though I'm sure plenty are still out there, but still save yourself the worry!
With the vacuum / intake leak issues and the rough idle sorted, a rough transition into the upper rev-band had developed where the Vanos-system opens up fully. Time for a Vanos rebuild then, with new Teflon seals and Viton O-rings, but not wanting to sell himself short after going to this much effort he decided to plump for a full upgrade kit that supposedly boosts top-end power.
