BMW Senior Six Registry FAQ: Fuel System: Zenith Carb Rebuild

BMW Senior Six Registry

FAQ: Zenith Carb Rebuild

Page 1: Remove the carb

Page 2: Disassemble the carb

Page 3: Reassemble the carb

Page 4: Reinstall the carb

NOTE: This removal is specifically for the carb nearest the firewall. I don't have a similar list for the forward carb, since it was much simpler to get at. All the items to remove for the carb are the same, and there were fewer ancillary things to move around to get good access.

  1. Disconnecting the carb
    1. Disconnect the battery negative terminal. No reason to have any chance to short something out.
    2. Remove the air filter housing cover. If you've never done this before, you should probably stop here and not attempt a carb rebuild :^)
    3. Remove the two nuts on top of the carbs which hold the air filter housing in place. Remove the air filter housing (being careful to keep the any attached hoses nearby).
    4. Disconnect the fuel inlet hose at the carb inlet block (loosen hose clamp, remove and plug hose). Label it.
    5. Disconnect the evaporative line from the bottom of the carb inlet block (loosen hose clamp, remove and plug hose). Label it.
    6. Disconnect the vacuum line to the rear intake manifold (on the drivers' side). Label it, note that it is connected to a "T" with the vacuum line to the base of the front carb and to the canister that lives below the battery.
    7. Disconnect the vacuum line to the base of the carb on the drivers' side. Label it, note that it is connected to a "T" with the dashpot mounted on the firewall on the drivers' side (white vacuum line) and the middle of the 3 dashpots on the passengers' side of the firewall.
    8. Disconnect the wire to the automatic choke. Label it.
    9. Disconnect the wire to the shutoff valve connector. Label it.
    10. Disconnect the carb linkage at the ball-and-socket joint.
    11. Disconnect the vacuum line which leaves the carb base parallel to the #4 cylinder intake manifold pipe. Label it.
    12. Disconnect automatic choke water lines. Lable and plug. Note that the "inner" (closer to the head) line goes to the forward carb, while the "outer" (further from head) goes to the block.

  2. Stuff to make it easier to unbolt the carb
    1. Disconnect the wires to the back-of-the-head sensor. One for the center of the sensor, one for the side of the sensor. Label them.
    2. Disconnect the ground wire from this wiring harness to the firewall in the center of the car.
    3. Disconnect the wire to the front carb automatic choke.
    4. Disconnect the wire to the front carb connector to the shutoff valve
    5. Move the wiring harness (to which all the wires above belong) out of your way.
    6. Remove the dashpot on the drivers side firewall. Two screws hold it to the firewall. It's got a few vacuum lines going to the set of 3 dashpots on the passenger side. Just lay it near those (after labeling anything you had to disconnect)
    7. Remove the radiator overflow tank. First, disconnect the large hose to it (from the block?). Then, unbolt the 10mm bolts that hold it to the firewall and the inside wheel well (near the master cylinder).

  3. Removing the carb
    1. Loosen and remove the four nuts attached to the carb studs that stick out through the bottom of the manifold. This is a job for finesse, small hands, 1/4" drive ratchets, and anything else you can think of.
    2. Do a visual inspection to make sure there is nothing attached to your carb.
    3. Lift the carb off the manifold; go slow, don't drop it or break anything now.
    4. Put the carb somewhere and cover the manifold so tiny stuff doesn't fall in.

You are done. Take a break.