3 replies to this topic

[1275MIN]

Hi all,

Just a quick one. I have just fitted some twin carbs and the fuel mixture needs settin before i start the engine. I have in my head 12 flats ie 2 turns but cant remember if its from the top or the bottom! any chance you can confirm it for me? Its olny to get the engine started!

[karlos_junior]

sorry to hijack but I need to know this too as Im about to put my new rebuild car on and it would be real helpful to know how to set to start from...

[dklawson]

For a starting position, turn the nuts out 2 full turns (12 flats as you said) DOWN from when the jet is flush with the bridge. You should center the jets first though.

Once the engine has started and warmed up you will need to turn the engine off, disconnect the throttle and choke linkages and back off the fast idle screw. Back both the regular idle screws out until both butterflies are closed then turn the each screw IN one full turn after their ends first touch the stops. Restart the engine and bring the RPM up to normal (for your engine) using both idle screws. Adjust each idle screw independently while using a carb synch tool to balance the air flow between the front and rear carbs. At this point you position and tighten the actuator levers on the throttle linkage. And so on and on.

For an overview in print, check out Haynes or the SU tuning manual. For visual instruction, visit YouTube and search for the British car videos by John Twist of University Motors. They have several videos including how to balance and tune SU carbs.

[karlos_junior]

thank you very much.