I have a 84' Opel Rekord 2.0s (GM) with a Varajet 2 carburettor that's been there since new.
It only has a 100,000 miles on it, but I suspect it's running rich. Spark plugs are heavily carbon deposited/sooted, one of them had some oil on the threads. (New coil, and new plug leads). I have a K&N "sports" filter, but both with and without it the carburettor is making a loud sucking noise on idle (varying, averaging 800 rpms) that dissapears when I give throttle, and I can't find any leak. It'll often hesitate a bit at low rpms as well with a little grunt if that makes sense.
The carburettors mixture settings cannot be tampered with unfortunately, you can only adjust the idle speed and an idle bypass screw. It drives well in high speeds however, only low rpm hesitation. Considering throwing it all out and rebuilding it to a fuel injection system instead if it can't be solved.
Any help or advice is appreciated!