How to Center the Jets on SU Carburetors

Understanding how your vehicle's engine functions and having the ability to correct a problem can save you time, money and the hassle of taking it to a professional mechanic. One of these functions you can repair yourself is the centering of the jets on an SU carburetor.

Instructions

1

Use a spark-plug socket wrench to loosen the locking nut on the bottom of the assembly. Use a 5/8" socket to unscrew the mixture nut just below the locking nut. Pull the jet out and remove the mixture tension spring.

2

Replace the jet and mixture nut, then tuck the nut and jet up as far as they will go. Disconnect the mixture linkage. Remove the two nuts on the piston cap. Before completely removing them, mark the jet and nuts with a permanent marker. If they go back on incorrectly, it could cause problems.

3

Flush the shoulder of the needle in the piston with the piston body. Screw the needle down tight and place the piston in the keyed passageway. Listen for the "click" as you check to see if the needle swings freely. The "click" will indicate proper seating. If there's no "click", then try to re-seat again.

4

Re-install the parts you removed, the whole time listening for the "click" whenever the needle moves. If at any point you don't hear it, it is likely it bumped out of place and you will need to start the process over. At the end of this process, move on to setting up your carbs. You should consult a Haynes or Chilton manual for this.