• S.U. Carburetor Kick-Down Adjustment

    Tony's Tip #4:

    One of the most typical problems with the S.U. carb is that users find they need to momentarily depress the accelerator pedal to the floor in order to cause the inertia of the return spring driven mechanism to bring the carb back to its normal idle speed. This action is typically called, "kicking it down." Many suffering with this problem try to fix it by changing return springs, tightening (by turning) throttle shaft springs, lubricating the ball joints, installing new throttle shafts, rebuilding the carbs, and ultimately, buying new carbs. None of those actions will fix the problem. The problem can be fixed by adjusting and tightening the solid inter-linkage shaft. This problem I've suffered with for decades was fixed within minutes by someone who knew how to calibrate the carbs and that person did not even need to rebuild them. Unfortunately, I have not found any written instructions as to the exact procedure to adjust the inter-rod link, nor the other adjustments on the various ball joint connectors on the S.U. carbs, but I was lucky to find someone who was able to make the adjustments despite not having written instructions as to how to make any of the many adjustments on the various linkage shafts and joints. Sure, there are many written instructions on adjusting the carbs themselves, but I haven't seen any addressing the exact procedure of adjusting all the connecting rods and joints. Bottom linen is if your carbs need to be kicked down for the engine to return to idle, the problem may NOT be in the carbs themselves.
    Comments 5 Comments
    1. TimK's Avatar
      TimK -
      I've had this problem for the 32 years I've had my Healey. Now to figure out what to do to the inter-rod link -- not clear from above (how, for example, do you adjust and tighten a solid shaft?)
    1. healeymanjim's Avatar
      healeymanjim -
      I have two healeys and both have the carb linkage adjusted so that the throttle plate roller lies midway in the fork of the linkage. I had always understood this to be the correct position. the carb spring is supposed to pull the throttle plate closed, not the throttle linkage spring in the cockpit. I also have the "kickdown" problem along with other healeys in our club. I could be doing this wrong and would also like to know a better way.
    1. trrdster2000's Avatar
      trrdster2000 -
      I think what CDToaster is trying to explain is the ends of the linkage. They have little balls that ride inside a housing that is spring loaded. They do go flat due to lack of lubrication and tend to stick. If you have four or more in your system, the potential for high idle or inconsistent idle is always there. Take the split pins out and clean the inside of the shaft after getting the spring and rider plug out. Lub with high heat grease and put it all back with free play in each joint. Replace those with flat spots. You will find all to be smoother and use less effort.
      Good rainy day afternoon job, no not on the kitchen table.

    1. Jayplum's Avatar
      Jayplum -
      I have this exact issue. How is this adjustment done?
    1. blhazzard's Avatar
      blhazzard -
      I am just completing a rebuild of my 67 TR4A. I had inspected the throttle linkage and found all had serious flat spots on pivot balls in joints.
      After trying to find replacement pivot balls (unsuccessfully) I just ordered all new links which come with new ball joints.
      Now installed the system work well with no binding or dead spots.
      Carbs kick down without the need for a "momentarily depress" of the pedal.

      Two questions...
      1) Recommendations on grease for these Moly, Lithium, ?
      2) Does anyone have a lead on a throttle pedal shaft assy and the bushings for a TR4A. My shaft has a grove cut into it by the bracket while the nylon end bearings were very worn. I am afraid this shaft is going to ultimately fail. Moss and others show the shaft and bushings but do not show then as available as new.