SU Carb Linkages and Return Springs

HS   HIF CB   HIF RB   V8

HS: View from the RHS of the car leaning over the engine. The choke linkage is towards the top of the picture (with return spring) and the throttle at the bottom. The clamps at A are set so that both carb butterfly cams start opening at the same time, and those at B are set so that both jets start to move down at the same time. The clamps also need to be set such that they and the interconnecting shafts can move back and fore between the two carbs a small amount so the shafts can rotate freely, but not so much that the clamp fingers can become disengaged from the butterfly and choke cams. There needs to be a few thou free play between the throttle spindle finger and the choke spindle at C:


And from the other side of the car with the throttle linkage (and two return springs) towards the top of the picture and the choke at the bottom. This picture also shows the attachment points for the springs in the heat shield. Two slotted holes in the bottom edge at right and left for the carb return springs (1); a tag sticking out for the choke return spring immediately to the left of the throttle operating finger (2); and two more unused plain holes either side of that (3):


A replacement heat-shield has three tabs and three holes:

View from the front of the car. The rear carb is at the top of the picture (don't be confused by the free end of the choke cable, it is not attached to the choke clamp on the rear carb). The rear carb accelerator return spring located in the hole in the clamp (arrowed), the front carb is a mirror image:


The choke return spring located in a hole in the operating lever (arrowed):


The throttle return spring does not have a hole to attach to but on my car is simply hooked over the pin of the cable clamp (arrowed) where it goes through the operating finger. This makes me think that it is a later addition as the other attachment points - throttle clamps and choke operating finger - have holes specifically for the spring:


HIF CB: Chrome bumper - export 1971-on, UK 74-on, 18V engines with HIF carbs. Although they had the same accelerator cable bracket as the later rubber bumper cars with the 'top-down' choke cable, they retained the 'bottom-up' arrangement of HS carbs, with the outer against the choke lever and the inner secured with a screw in a hole in the accelerator cable bracket. This installation shows a return spring on both choke quadrants (blue arrows):


HIF RB: UK 78, a choke quadrant spring on the front carb and another on the throttle cable, 'top down' choke cable:


The clamps need to be set such that they and the interconnecting shafts can move back and fore between the two carbs a small amount so the shafts can rotate freely, but not so much that the clamp fingers can become disengaged from the butterfly and choke cams.

No holes in the throttle cam (arrowed) or underneath it in the heat-shield flange:


No holes in the choke lever (arrowed), although there is a spare hole underneath it in the heat-shield flange, and no spring on the rear carb choke quadrant:


Slightly clearer view of the clip holding the accelerator cable and pin to the carb operating lever. It is a folded and forked spring-clip that slides into a slot on the open end of the pin. Again no spring on the rear carb choke quadrant, with an unused tab on the heat-shield nearby:


Workshop Manual drawing showing just two springs (7), with the left-hand one going to the throttle cable (1) leaving the right-hand one angled towards the rear choke quadrant. This is different to the two examples above where the choke spring is on the front carb quadrant:

V8: Vee's accelerator return spring (middle) with one of my 4-cylinder return springs (top) and a new one sold as being for the V8 (bottom). The pukka spring part is actually slightly longer than the other two, which are pretty much the same size, it's the wire hooks that are the main difference. The 4-cylinder overall is 2.75" as stated elsewhere, Vee's spring 2.5" and the pukka spring 2" and not the stated 1.75". Despite Vee's spring being 2.5" it is not loose when fitted, but I have fitted the new one and will see if I can find any differences. Given the only real difference is in the wire hooks it would be easy to modify a 4-cylinder, maybe that is what a PO did on Vee: