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Rpm still not better


Well-known member
Oct 27, 2011
The Dalles, Oregon
This is my approach to every SU style carb that comes into my driveway. So far, every one has left driving better than it came in.

If you plan to keep the SU?s, get a sync tool, jet adjusting wrench and jet centering tool from some British car store like Moss Motors. It?s a $100 that Is absolutely well worth it.

Try resetting all fuel and air settings. Warm it up first.

loosen linkage. Back off choke and idle set screws until there is absolutely no contact. Back the chokes off an extra full turn.

Get the throttle screws to just touch the stop, then give them 1.5 turns.

Raise the jets to the bridge. make sure they are all the way flush with the bridge in the carb throat. Pull the dashpot dampers and check that the piston falls with a clink. if not, recenter the jets.

Lower the jets 12 flats (2 full turns). check that the piston falls freely to the bridge. Put the dampers back in.

Start the engine. It should idle high, so get it back in line by adjusting each carb. Use a sync tool and get the air flow correct, and idle where it should be.

Lift the front carb piston 1/8" and see what changes. If it stumbles, richen by 1 flat, if it raises the idle lean it by 1 flat, and blip the throttle after each adjustment. Do the same to the rear. Go back and fourth until lifting the piston doesnt change the idle speed.

Make sure that they are even and balanced. Make sure that all other things are correct. So valve lash, and ignition timing. Vacuum leaks are a huge problem, so check for vacuum leaks again.

If you dont have a sync tool. Go to the hardware store, and get some clear tubing (about 12 feet) a yard stick, and a couple packs of zip ties and make a manometer. Pretty easy.