SU Fuel Pump and Regulator Tips

At our November 1999 General Meeting our guest speaker, Bob Tait gave an interesting talk and demonstration on the SU fuel pump and RB106 regulators used in many of OUT cars For those who missed the meeting, and those who now can’t remember the plethora of facts presented, following are the tips Bob gave from his years of experience.

SU fuel pump tips

There are 11 rollers spacing the diaphragm, all must be between 0.427″ and 0.431″ diameter.

  • Adjust the diaphragm height so it just toggles, then back it off 6 holes.
  • Face the valve disks on 1200 grit wet & dry , then work them onto their seats in a circular motion with a scriber using Brasso as a cutting compound until a good air tight seal is obtained.
  • Mount the outlet uppermost, drain hole at the bottom.
  • The diaphragm rubber should have a very small hole inside to lubricate between the rubber pieces and prevent drying out of the rubber.
  • Fit the solenoid/body screws loosely and hold the diaphragm up at the toggle before tightening.
  • Electrically earth one of the screws.
  • Push on the upper contact – there should be an even distance between the roller and the contact.
  • There should be a 0.05µF capacitor (or 0.047µF if unobtainable) across the contacts as a spark suppressor.
  • The coil should have 6 ohms resistance (3 1/2 ohms for a 6V coil) and it will draw 2 Amps.
  • A good pump should give one tick every 2 minutes and deliver 1 l/2 psi pressure.

Regulator tips (for the RB106 regulator)

  • Armature airgaps should be 0.015″ for the voltage regulator and 0.20″ for the cutout.
  • The screws on the back of the windings adjust the voltage setting and cutout closing voltage.
  • Undo the top contact screw and loosen the bottom one to allow the contact set to be pushed aside for cleaning without disassembly.
  • Cutout is adjusted so the contact just moves when the armature is pressed down all the way.
  • Connect a voltmeter to E (earth) and to the metal body of the coils.
  • Adjust the voltage regulator screw (at 2000rpm) to 15.5V open circuit (paper between the contacts).
  • This will regulate to 14.2V when in circuit.
  • The cutout closes at 12.6V and is adjusted with the screw on the back of the coil.
  • Lower the motor speed and adjust the reverse current setting (by bending the tag on the armature) to -1Amp (large gap) to -4Amp (small gap) on an ammeter.

Bob Tait