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Zenith carb leaking air

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

  1. 62SNBMR

    62SNBMR Platinum Level Sponsor

    Disassembled the rear carb tonight. Throughly cleaned. The accelerator pump piston and chamber are clean. No restrictions. Nozzle is clean and ball bearing present. All passage ways cleaned. Reassembled it with new gaskets. One thing I did notice was that the nylon roller on the accelerator pump lever is difficult to spin. It catches the cam and doesn't move smoothly. Tried freeing it with a WD-40, etc. and just not getting loose. Not sure if this is a part that is available. Suggestions?
     
  2. 62SNBMR

    62SNBMR Platinum Level Sponsor

    Ok, I removed the rear carb last night. Disassembled it, thoroughly cleaned it again. Accelerator pump works fine, no restrictions. The nozzle is fine, ball bearing intact. Cleaned out all passageways. New gaskets. Upon reassembly I noticed that the nylon/ plastic roller on the lever arm that contacts the cam is difficult to turn. Tried cleaning, lubricating, etc. but no luck. This may be causing some of the problem. Instead of a smooth action as you accelerate, the cam hangs up on it, then slides past it. Was looking online for replacement parts but no luck and doubt they exist. Anyone run into this problem?
     
  3. bernd_st

    bernd_st Bronze Level Sponsor

    Doesn't sound good. The nylon roller needs to move freely- many don't. Try compressed air holding the air pistol very close to the roller center. Normally any dirt or blasting remains will fly out. WD 40 treatment afterwards and it should turn freely again. No whatsoever replacement parts anywhere. Only better used ones if you find any. The cam should not hang up nor sliding past it. Sometimes the lever with the roller is bent either inwards or outwards, so make sure it's centered and riding on the cam properly...
     
  4. 62SNBMR

    62SNBMR Platinum Level Sponsor

    Well, no good news to report. Now it won't idle. And, the rear jet stream is not as strong after cleaning, new gasket, etc. Still getting considerable lag when I throttle up to the point that it stalls out. Have to keep feathering to get the revs up, then it's ok. What else could be affecting the pump stream? Ball bearings are present and in the correct location. Both pistons were clean, no corrosion. Walls of the carb clean, no corrosion. I did tweak the lever with the roller a bit to make sure it lines up wit the cam. When I did get it to idle at around 1300- 1500 rpm, checked with the Unisyn tool and both carbs were sync'd. Just won't maintain a lower idle speed and dies out.

    As for the lever with the roller, thought about grinding off the rivet end, freeing up the roller, then drill a hole in the shaft end (assuming it's solid) for a small washer and screw.
     
  5. bernd_st

    bernd_st Bronze Level Sponsor

    Hmm, tricky. Did you check the accelerator pump non return valve ? It's the little wire meshed device sitting at the bottom of the float chamber. Screw it out and blow it through with compressed air. Take the piston out again and blow air through the small supply channel. Setup can be seen on the WSM picture attached.

    If above still doesn't improve things you may take out the idle jet and blow it through too. Same to the slow running passages. By the way : Did you confirm whether the throttle spindle on the affected carb doesn't show too much play ?

    IMG_20201003_100811.jpg
     
  6. 62SNBMR

    62SNBMR Platinum Level Sponsor

    When I disassembled the carbs I blew the passages with aerosol carb cleaner. Didn't stick anything down them for fear of causing damage, etc. I did remove the accelerator pump non return valve as well, but didn't blow compressed air through it. Was able to blow air through it the old fashioned way. Didn't detect any movement in the throttle spindle on both carbs. I had earlier removed the idle jets and blew carb cleaner through the jets and passage ways of both carbs. Do you typically adjust the Throttle Fast Idle Gap? Looks like this is only done on the front carb? The rear carb doesn't have the same linkage and set screw.
     
  7. bernd_st

    bernd_st Bronze Level Sponsor

    Compressed air obviously works better than just carb cleaner since it removes all potential residuals. Did you check whether the float height is even between front & rear carb ? A common mistake is to place to many washers under the float valve limiting the travel to much. Is the float on the faulty carb travelling upwards with fuel level ? Rare but have seen floats with small hole in it and therefore not swimming properly.

    Regarding fast idle setting, yes I do it however not with the proper sized drill, but according to feel & experience. Perhaps time to post some pictures of your faulty carb here...
     
  8. 62SNBMR

    62SNBMR Platinum Level Sponsor

    Bernd,
    Been struggling a bit, but finally got the carbs back together and running decently. Balanced using the unisyn tool. Idling at around 800 rpm. Much smoother. Flow out of each carb good. Float are solid and levels were equal. However, still getting lag when you hit the accelerator. This time it's not dying out, but still a definite lag. I did notice a little play in the carb throttle spindles, but not sure what is normal.
     
  9. bernd_st

    bernd_st Bronze Level Sponsor

    Sounds as if you are making progress. Lag shouldn't happen though. Are the choke flaps completely open once the choke cable is pushed fully home ? Movement synchronous ?
    There should be no noticeable spindle play. Is it worse on the rear carb ?
     
  10. 62SNBMR

    62SNBMR Platinum Level Sponsor

    Yes, spindle play slightly worse on rear carb. Choke flaps completely open when choke cable pushed fully in. However, I've discovered that after revving the engine several times, the rear carb fuel flow (accelerator pump) diminishes significantly. Something must be in a passage way. Tearing it down again today and putting compressed air through it.

    Yesterday I discovered the hard way that my heater radiator has sprung a small leak. Off to the radiator shop.
     
  11. bernd_st

    bernd_st Bronze Level Sponsor

    Diminishing fuel flow is certainly the main reason for the lag. Hope compressed air will free the passages.
    Sprung radiator is bad luck on top...
     
  12. 62SNBMR

    62SNBMR Platinum Level Sponsor

    Used my neighbors air compressor and thoroughly blew out every hole. It's back on the car and still have a little lag. Been playing with the air/fuel mixture. It's idling ok, still have lag. And I noticed that the fuel flow is not like the other carb. It produces a strong stream. Not so much on the second carb. Wondering if the piston is worn? Have a spare piston from another carb I might try.
     
  13. bernd_st

    bernd_st Bronze Level Sponsor

    Sounds like worn piston/bore or faulty Non Return Valve...
     
    Last edited: Oct 6, 2020
  14. RootesRacer

    RootesRacer Donation Time

    Consider that the progression holes under the throttle plate may be clogged.
    The accel pump is important for transient enrichment but the progression holes are responsible for static running off idle.
    If the progression circuit is not working, the accel enrichment will not fill that hole.
     
    beamdream likes this.
  15. beamdream

    beamdream Gold Level Sponsor

    Good point, nevertheless the "diminished " flow from the accelerator pump is still a problem.

    Wondering if swapping the accelerator pump components from rear to front carb might be worthwhile, just to see if the problem moves with them.
     
  16. 62SNBMR

    62SNBMR Platinum Level Sponsor

    Gentlemen,
    Have found something interesting. The accelerator non return (or check) valve may be the issue. I found two check valves from an old WIP 36 set and they were different. See picture. My check valve, on the right, has a small hole in the middle. Same with the other carb. I can blow air in both directions through this check valve with the hole. The other check valves without the hole don't allow air in both directions. Could this be the culprit?
     

    Attached Files:

  17. 62SNBMR

    62SNBMR Platinum Level Sponsor

    I've reassembled using the check valve without the hole and can already hear a big difference when moving the lever arm. To verify, I put the old check valve back in and can hardly hear any sound. Would have put it back on the car for the final test, but the o-ring on the main jet was damaged.
     
  18. RootesRacer

    RootesRacer Donation Time

    Yes, this is a accel pump bleed orifice. You will want a matched set (both having or not having this feature).
    Having the orifice makes small or slow changes in throttle opening NOT result in a squirt which is better for fuel economy.
     
  19. 62SNBMR

    62SNBMR Platinum Level Sponsor

    Okay, both need to match and it's better fuel economy if you use the orifice with the small hole? Another thing I notice is that the rear carb at idle has a very small dribble of fuel coming out of the accelerator pump discharge nozzle. Front carb doesn't have any fuel coming out until you hit the throttle. What could be causing that?

    Another change that I made to the rear carb was a better throttle valve that didn't have any play in it. Glad I never throw any parts away!
     
  20. 62SNBMR

    62SNBMR Platinum Level Sponsor

    SUCCESS! I found the culprit!! The check valve or accel pump bleed orifice is not functioning properly on the rear carb. I swapped them between the carbs and the problem followed to the front. Now the big question - does anyone make these anymore? I have a pair that do not have the small hole in the middle. Guess I'll give them a try to see what happens.
     

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