Triumph Repair/S U carbs


Hi Howard, I was reading your S U carb adjustment for twin carbs on a 75 Spitfire.  I have that setup on a 79, but my carbs don't seen to have the lift pin you refer to.  Do I have a pair that is incorrect?  I cant find any markings that indicate HS2 or HS4 etc.. Thanks so much.....Rory

Hi Rory,

The 79 Spitfire didn't have SUs so someone put them on or it is Euro version that did have SUs.

I never seen an SU without the lift pins under the lip of the top pot. But that don't matter as you can just remove the airfilters and put a flat blade screwdriver in under the piston and rotate it so as to lift the piston to the width of the blade and adjust the other carb jet. But don't forget to first synchronize the throttle shafts first and the throttle stop screws before trying to adjust the jets also make sure the ignition timing is set first.

The same procedure works with Stromberg carbs too.


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Howard M. Fitzcharles III


Triumph TR-4 up & Spitfire, and Engine theory


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

Associate member SAE EAA member

Import Car magazine

ASE Master Auto with L-1 certification up to 2000

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