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Replacing CD 150 in '69 Alpine

Discussion in 'Huskies, Imps, Rapiers, Fastbacks, etc.' started by Bill Blue, Oct 3, 2021.

  1. 260Alpine

    260Alpine Silver Level Sponsor

    I've went up to 10 -12 initial and 34 total with 10 degrees in the can. Centrifigal advance should be all in by 3500 RPM. Worked great for a wide assortment of vehicles. I prefer manifold at idle and light load. You will have to slow the idle down a bit when going from ported to manifold. Most people who have switched noticed smoother idle, throttle response and better mileage. Runs cooler on a hot day.
     
    Last edited: Oct 12, 2021
  2. Bill Blue

    Bill Blue Platinum Level Sponsor

    Except the actual port (the brass fitting) has at least two other air sources. One is a port subject to intake air flow on the far end of the carb. The other source(s) is currently unknown to me, but I can hear air sucking. So I doubt it experiences manifold vacuum when the throttle is closed. I can post a pic of the second air source if that would be of value.

    Bill
     
  3. Bill Blue

    Bill Blue Platinum Level Sponsor

    So I should be able to live with whatever is there. Just need to try stuff until I find something that works. Sort of like tuning the carb.
    Bill
     
  4. Bill Blue

    Bill Blue Platinum Level Sponsor

    Found the third (and last) source of air. It is filtered, unmolested atmospheric air, needed for the fuel mixture enrichment circuit. Why it would be connected to the dizzy vacuum port is way, way beyond me.

    Bill
     
  5. Bill Blue

    Bill Blue Platinum Level Sponsor

    Starting to look like a fun project. Tee the carb into the fuel system, run the engine to determine if a regulator is needed. Remove the intake manifold and bore out the throat to whatever is possible, but no more than 1 7/8". Make adapter plates (one to bolt to the manifold, one to bolt to the carb), assemble and tune. Make adapter plate to mount the air filter housing. Should take no more than an afternoon:rolleyes:.
    Bill
     
  6. Barry

    Barry Platinum Level Sponsor


    A good picture is nearly always useful.
     
  7. Barry

    Barry Platinum Level Sponsor




    Bill,

    Neither H-D nor S&S used a canister style vacuum advance distributor, so I do not understand your reference to "the dizzy vacuum port" on the S&S carb. What am I missing?
     
  8. Bill Blue

    Bill Blue Platinum Level Sponsor

    My ignorance. I know zero about any motorcycle, including how they manage spark advance. I could see that the port was subject to pressure changes, so assumed it was a spark control port.
    Bill
     
    Last edited: Oct 13, 2021
  9. Bill Blue

    Bill Blue Platinum Level Sponsor

    The port is the black circle in the throat.
    IMG_8014.JPG
     
  10. Barry

    Barry Platinum Level Sponsor

    Bill,

    Based on proximity, the "black circle in the throat" (in front of the throttle blade) shown in post #49 is likely a source of filtered air for the cold start enrichment circuit. That is consistent with your comment in post #44. The extra fuel has to get into the intake somewhere and that is almost certainly the "black circle" behind the throttle blade shown in the picture in post #36.

    It seems to me that the "black circle" behind the throttle blade shown in the picture in post #36 probably has several functions including cold start enrichment, positive crankcase ventilation and providing a manifold vacuum signal to a VOES based vacuum advance system. Additionally, I suspect that the top of the "float chamber" is connected to the "black circle" behind the throttle blade shown in the picture in post #36 to provide rudimentary control of gasoline vapor emissions from the carb float chamber.

    I am pretty sure that the single external hose connection port (the brass "vacuum hose" fitting) will show full manifold vacuum when the engine is running. You may be able to jury rig some sort of ignition vacuum advance system based on manifold vacuum, but I don't see any way to achieve traditional "transition port" vacuum advance. Your "Fastback Alpine" engine appears to be very tame which generally results in a lot of manifold vacuum at idle. Connecting a high (maybe 20+ inches of Hg) level of vacuum to a traditional canister style vacuum advance distributor will probably result in something like 25-30 degrees of total ignition advance at idle. A lot of high performance engines use "locked out" distributors with no mechanical advance which means something like 35 degrees of ignition advance at idle, but that is a different world.

    I am not disparaging your use of the S&S carb, just trying to clarify how I think it works.
     
  11. husky drvr

    husky drvr Platinum Level Sponsor

    Bill,

    Have you considered locating and drilling the carb body for your own ported vacuum port?

    With just the two pics it's difficult to tell, but it looks like a possible option. Yes, I'm aware drilling the port might be a lot easier than keeping a hose connected.
     
  12. Bill Blue

    Bill Blue Platinum Level Sponsor

    Not really considered the possibility. Locating and sizing the port is something I have no knowledge of. Sure, I know the port has to be uncovered by the throttle blade, but that's all I know. I think there might be a suitable spot to drill, but it all depends on where the spot should be, doesn't it? Might be a possible solution if if all else fails.
    Bill
     
  13. Bill Blue

    Bill Blue Platinum Level Sponsor

    Barry, I find it fascinating that the two holes are in any way, connected. Can't help but think it is to moderate the vacuum signal. Or maybe to provide air passage while the throttle plate is closed. My mind cannot project air flow and vacuum created by the two holes subjected to airflow which at times are of very different and at other times very equal nature.

    Forget PCV stuff on this carb, there just isn't any. There are only two items connecting the carb to the outside world. Both are brass nipples. One is float bowl overflow and the other is the vacuum nipple. The largest orifice is the vacuum nipple at less than a sixteenth.

    Bill
     
  14. Bill Blue

    Bill Blue Platinum Level Sponsor

    Another prickly issue of drilling a port. How would the nipple be attached? The throat wall is .233". More than I would have imagined, but way less than what is required to drill and tap. Light press fit with Red Locktite?
     
  15. 260Alpine

    260Alpine Silver Level Sponsor

    Bill, Probably just interference fit 1/8" stainless tube. Check your old carb for location. Some cars came with manifold vacuum advance. Easy to make a stop to control the movement of the vacuum can to about half of what is stock.
     
  16. Bill Blue

    Bill Blue Platinum Level Sponsor

    Jim, keep in mind the old carb is a CD. Spaghetti tubing attaches onto the carb close to the filter. Looking into the carb, it is apparent that is not the actual port location. No idea where it may be. Also, the tubing forks, each branch feeding a "can". Guess it is time I looked into the stock Alpine vacuum setup. But if memory serves me correctly (not a given), the Alpines use manifold vacuum.

    Bill
     
  17. 260Alpine

    260Alpine Silver Level Sponsor

    Bill, the Alpine distributor would be a perfect solution if for manifold vacuum.
     
  18. husky drvr

    husky drvr Platinum Level Sponsor

    Bill,

    If you have a vacuum connection on each side of the can, then one of them is a retard for emissions purposes.

    All Alpines use a "ported" vacuum source, not manifold vacuum.

    I checked a few carbs I have and noted that all their vacuum ports entered the throttle bore ~45 to 75 estimated degrees to throttle shaft, adjacent to the side of the blade that pivots toward the carb entry, and from just above the blade to partially blocked by the edge of the blade, all port sizes estimated ~0.020 inches or smaller.

    Thinking about it, a larger port, a port located closer to the blade shaft, or above the top edge of the blade would all delay the initial vacuum signal delivery.

    Hope this helps,

    Don
     
    Last edited: Oct 15, 2021
  19. husky drvr

    husky drvr Platinum Level Sponsor

    Even disregarding the vacuum issue, the mechanical advance curve would give much better drivability than what I presume to be in his emissions distributor.

    Don
     
  20. Bill Blue

    Bill Blue Platinum Level Sponsor

    Two cans driven by one source of vacuum is a bit more than I can understand.

    Anyway, I'm thinking I will wait and see what happens when a stock S&S carb is mated to a stock '69 Alpine dizzy with two cans. For all I know, it will work perfectly. It's for sure that mating an unknown with an unknown leads me down an unknown path, as does mating a known with an unknown.. However, I've decided that the homemade vacuum port would be easy (even if wrong) and easily remedied with a dab of JB, so it will probably be at the head of the list of possible actions to take.

    Bill
     
    Shannon Boal likes this.

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