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Zenith carb leaking air

Discussion in '"Stock" Alpine' started by 62SNBMR, Sep 16, 2020.

  1. 62SNBMR

    62SNBMR Donation Time

    I have a 62 Series II with the Zenith WIP carbs. Having an issue with the second carb. Using a Unisyn tool, front carb is fine, back carb not registering much air flow. I've check gaskets, mountings, etc. No air leaks that I can see. Not too long ago they were both fine. Suggestions welcome. Thanks
     
  2. RootesRacer

    RootesRacer Donation Time

    Got synch?
     
  3. 62SNBMR

    62SNBMR Donation Time

  4. RootesRacer

    RootesRacer Donation Time

    No disrespect intended here, but synchronization is what makes the flowmeter read the same on both carbs.

    Disconnect the throttle link, adjust each throttle stops on each carb so that they read the same flow, then reconnect the throttle link.
    Adjust idle mixtures and repeat till its running right and reads the same on each carb.

    Make sure that the throttle link fully allows independent adjustment (common problem).

    Make sure that you have no obvious leaks (carb base gaskets, dizzy vac advance line ECT).
     
    Last edited: Sep 17, 2020
  5. alpine_64

    alpine_64 Donation Time

    The zeniths have a habbit of gwtting air leaks around worn throttlw spindles... Bernd who frequents the site makes replacements
     
  6. bernd_st

    bernd_st Bronze Level Sponsor

    True. I'm able to help with repro spindles. But wonder whether that's the root cause here. Have you checked the rear carb for excessive throttle spindle play ? Are both butterflies moving synchronous when you push the throttle pedal ? Sometimes the connector between both carbs spindles gets loose which means the front one will operate normally while the rear one just remains on idle position...
     
  7. 62SNBMR

    62SNBMR Donation Time

    Thanks for the suggestions. I'll double check everything and let you know if it works.
     
  8. 62SNBMR

    62SNBMR Donation Time

    Ok. I've checked the points, timing and re-sync'd the carbs per your instructions above. At least now I'm getting more balanced readings on the unisyn. Not perfect, but much, much closer. Trouble I'm having now is I'm still getting hesitancy when I throttle up from a standing start, and when I back off on the revs, the engine occasionally dies. Is it the air - fuel mix? Too rich? Too lean? Fiddled around with the needles but not sure what I'm doing. Didn't notice any change.
     
  9. beamdream

    beamdream Gold Level Sponsor

    Hesitation and dying would indicate lean mixtures, have you checked spark plug colours ? How about float levels?

    A bit more background info might help.

    Has this just started and it was running fine beforehand? Has the car been sitting for a while? Are the carbs correctly jetted?
     
  10. bernd_st

    bernd_st Bronze Level Sponsor

    Needles ? The Zenith's WIP/WIAs don't have any needles. Zenith/Stromberg's from a SV have them. Are you sure you're having the correct carbs on your S2 ?
     
  11. 62SNBMR

    62SNBMR Donation Time

    Sorry, I should say air adjustment screws. These are the original carbs. Haven't pulled the plugs to check. Car had been sitting for a long time. I'll just say that life happened and the car sat. Had to remove the gas tank, properly cleaned and sealed. Then replaced all fuel lines. Rebuilt the fuel pump. Pulled the carbs, dissembled them, thoroughly cleaned them, new gaskets, etc. Did other things as well not related like oil/filter change, new plugs, flushed coolant system, etc. In the past it always hesitated a bit upon acceleration. However, once the revs get up a little, it really pulls and runs smooth.
     
  12. bernd_st

    bernd_st Bronze Level Sponsor

    Alright then. Hesitation and dying out can usually be attributed to mixture leaning out. Would at first check the numbering on the top covers of your Zenith's. As you have a S2 it should 1744F/R. Main jet size should be 142 on both carbs. Take off the wire mesh air filters and give the throttle a few strokes. A constant good stream of fuel should be spayed into the Venturi from the accelerator pump nozzles. Check for even flow. Once you confirmed these we can carry on with our fault analysis...
     
  13. 62SNBMR

    62SNBMR Donation Time

    Bernd,
    Sorry for the late reply, have been out of town. Just checked and the carbs, they are stamped with 36 WIP 3, then 1800118 on the back carb and 1800119 on the front ( Serial Numbers?), then 1744 R. Not sure of the jet size. Where would I find that? is it stamped on it? When trying to tune the carbs I've been watching the fuel stream. They appear to have a good stream, even flow.
     
  14. bernd_st

    bernd_st Bronze Level Sponsor

    You have the correct Zeniths for your S2 then. 36 WIP 3s with 1744 F/R Code is proper. F stands for front R for rear. Either covers or bodies have been switched if front shows R. Anyway the brass main jets are located under the fuel bowls. Their size is imprinted so you can read from on the outside. Should read 142 on both carbs...
     
  15. 62SNBMR

    62SNBMR Donation Time

    Okay, looking through a small mirror, the reflection appears to read 142 on both. Front shows R, back shows F. Would that make a difference? I know when I rebuilt them, I did them one at a time, so I didn't swap the covers or bodies.
     
  16. bernd_st

    bernd_st Bronze Level Sponsor

    Main jets are fine & equal then. F or R is not substantial and you may just swap covers in the future. No internal difference. You said you rebuilt them. Did you make sure to heavily tighten the butterfly mount screws from the bottom which hold the carb body? Very often see cases where the carb body sits loose on the thick bottom flange gasket. If that's checked ok you could compare the float heights as the next step...
     
  17. 62SNBMR

    62SNBMR Donation Time

    Bernd,
    Two things - Reading up on the carbs and in one of my manuals they speak of the accelerator pump stroke. Looking at my carbs it appears they are both set up for the long stroke, if I'm looking at the right part. The fulcrum shaft end of the crank operating arm of the accelerator pump has two rectangular positions. Looks like my carbs are both set up for the long stroke. Good? Bad? Lastly, looking at the stream flow this morning, the rear carb is definitely not putting out as much fuel. Tested stream flow with several full pumps and there is a difference. Thanks again for your help.
     
  18. RootesRacer

    RootesRacer Donation Time

    I dont know if you have been inside the carb yet but zeniths use a solid metal piston for the accel pump unlike diaphragms used in most other carbs. Letting the fuel evaporste from the carbs during disuse can gum the piston and lock it in place or severely limit its stroke, both of which will reduce the accel squirt.
     
  19. bernd_st

    bernd_st Bronze Level Sponsor

    Not sure what you refer to as the long stroke, but the levers have to be attached to the uppermost rectangular opening on both carbs as default position. Racer is correct i.e. if fuel spray from one of the nozzles is less it may be caused by a gummed up accelerator pump piston. Actually they are made from brass and accessible if you take the top covers off. If they are not the root cause you should take off the nozzles and check whether the small steel balls are there and in place. Check the manual regarding further details on those...
     
  20. 62SNBMR

    62SNBMR Donation Time

    I'm reading from a Haynes manual and a Clymer handbook for those descriptions. I should check the workshop manual. Ok, will disassemble and clean/check pistons. Am familiar with the nozzles and that little ball bearing. Hopefully will get to it tonight. Thanks for your help.
     

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