Originally Posted by JamesJWeg
It's all very clean, I've rebuilt and cleaned them several times. Yes it is the correct parts, the dealer has even repaired it twice, they are at a lose as well. Part 15b does not tighten down on 14b, should it? The carb rubbers are lined up correctly. When holding part 13 with 14b, 15b and 4 assembled part 4 seems to have a lot of play. A few times the sholders on part 4 have worn completly off allowing it to drop. At other times 14b fails dropping 4 into the jet. Every time I replace 14b, I also replace 4 as well. This has happened so many times I have gotten it down to about a 10 min operation to replace 14b and 4 with new parts.
15b needs to tighten to hold 14b in place. The edge on 15b holds 14b in place, leaving 4 some wiggle room to move side to side, but not up and down, at all. If 4 can move up and down, even a millimeter, then 4 cannot ever be guaranteed to rise at the correct height. As well, if 14b is loose (up and down) in 13, it will vibrate and wear out the shoulders as you found and drop 4 into 2 and 3. 4 wears out together with 3 in normal circumstances only very slightly. 4 and 3 need to be replaced every 20K or so as a set, as 4 will wear due to rotational vibration and become out of round, letting too much fuel through 3. 14b is made of much harder material, hence wearing out 4. Normally, the fuel surface tension shields 4 and 3 from excessive wear. I think the fact 15b does not hold 14b down is your problem. Also remember that most mechanics never get to tinker with carbs and don’t get it taught in the BMW courses anymore.