• SU H6 Carburetor Will Not Decelerate

    I have a 1962 Triumph TR3B with SU H6 carbs. After a recent disassembly, cleaning and reassembly of the carbs the RPM would not return to idle after a load. It continued at an accelerated rate whether under load or at a stop - racing. Only by "goosing" the throttle with the accelerator did the RPM drop, but still not to the proper idle - 600 - 900 RPM (or anywhere close to it).

    I checked that each throttle plate was centered in the barrel, that they closed easily and no "daylight" around the edges of the plate. The carb pistons went up and down easily, dash pots properly filled with the right oil, jet needles centered in the jets and not binding. No vacuum leaks at gaskets.

    After much investigation I discovered that I had two problems: (1) the throttle return springs were not set in high enough torsion and (2) the coupling assemblies on the connecting rod were slipping under load. I could not detect slippage at curb idle by manually manipulating the throttle linkage but under load it seems the connection to #2 carb slipped. This allowed at least #2 carb to remain with an open throttle plate vs. #1 carb. The coupling was just tight enough to respond to "goosing" the accelerator but having slipped it was now out of balance. Also, the shafts are made of brass and over time will score from the connectors, also contributing to possible slippage.

    By torsioning the springs another half turn and tightening the connecting couplings I now have proper carburation. (Note: I also have a slight vacuum leak on #1 at the throttle shaft due to wear. This affects balance and fuel consumption but was not the cause of the "racing" problem)

    I hope this helps someone. I couldn't find a similar discussion anywhere.

    I have attached the Moss plate showing the connectors (66) and the springs (77):

    https://mossmotors.com/triumph-tr2-3...retors-su-h6-1
  • Recent Articles

    David Goble

    SU H6 Carburetor Will Not Decelerate

    I have a 1962 Triumph TR3B with SU H6 carbs. After a recent disassembly, cleaning and reassembly of the carbs the RPM would not return to idle after a load. It continued at an accelerated rate whether... read more
    David Goble 01-03-2019, 01:49 PM

    Categories:

    Technical  Triumph TR3 
  • Recent Forum Posts

    AngliaGT

    Re: Weather again

    The back yard yesterday morning.





    Was in the 40's today.Did the overdue oil change
    on the truck,&

    AngliaGT Today, 06:45 PM Go to last post
    NutmegCT

    Re: Weather again

    " ... and you eventually find yourself heading into the guardrail."

    Another triumph for AI!

    Yikes

    NutmegCT Today, 06:43 PM Go to last post
    NutmegCT

    Re: YouTube ads?

    Paul - a corollary to what you point out: us "mature" folks remember when TV wasn't inundated with ads. Today's kids, at least the ones I

    NutmegCT Today, 06:41 PM Go to last post
    pdplot

    Re: YouTube ads?

    My mother said it many years ago - you will someday pay for what you now get for nothing. Then came cable TV. You paid a monthly fee to be free of ads.

    pdplot Today, 06:38 PM Go to last post
    pdplot

    Re: Weather again

    Update. Easiest drive we ever had. Roads clear and dry until we hit the DC area and even then, there was a bit of wet spots including salt and I had to

    pdplot Today, 06:28 PM Go to last post
  • Recent Blog Posts

    MRC

    Jaguar Series 2 1970 Lucas Ignition Switch

    The Lucas ignition switch, 394150, completely fell apart. It is behind the actual lock and is the type where the steering wheel locks. I've got the thing off the column and verified the part number....

    MRC 12-29-2018 11:49 PM
  • Twitter