Rebuild instructions ---CLICK HERE FOR FULL INSTRUCTIONS ---

fd head.jpg

 It is important not to dismantle the FD more than nesasary, unless it is corroded or gummed up inside.

As most of the time the only part that has failed is the diaphragm.
Tearing it all apart & disturbing all the factory settings is not a good idea unless you have expensive Bosch re calibrating equipment,
The most important thing is not to mess with the factory preset misture screws on the individual ports.
After separating the 2 halves you will see the main fueling stem, this should just wriggle loose, & pull out. Remove all the o rings from it & the lower housing. Also if your fd is the later KE unit, pry off the retainer at the bottom of the fueling stem & remove the quad ring. Clean all parts, you can use alcohol, thinner, gasoline, kerosene or the shop safety clean. Avoid using carb cleaner as residues of this tend to destroy the seals in the pressure regulator on the earlier K units.
Once everything is clean start to reassemble the unit.
Tip #1 When fitting the small o rings to the metering slits, use one of the old o rings from the metering STEM & stretch over all the metering slit rings. This helps to keep them in place when inserting the fueling stem into the head. SEE PICTURE ABOVE.
Tip #2 Make sure that the slits on the metering stem line up EXACTLY with the fuel ports inside the head. Its ok to mark the position of one of the ports with a pen. While inserting the fuel stem roll up the old o ring & remove it as soon the stem is firmly seated.
Next replace all the cups & springs into the head. Its a good idea to take photos during disassembly, as this helps just in case you forget where something fits when the unit is being put back together, its ok to use a little grease to hold the white plastic plates & steel spring bases on the diaphragm, but only use the smallest amount. When pushing the 2 halves together make sure that you don't trap any of the plastic spring retainers, as this will crack them & may puncture the diaphragm at the same time.
All in all its a fairly straight forward procedure, just be patient & gently practice putting the two halves together a couple of times if this is your first rebuild.
Also when its back on the motor, remember that you may have to readjust the 3 mm mixture screw on the sensor plate just in front of the fuel distributor if the motor does not start straight away.