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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. Bill Blue

    Bill Blue Platinum Level Sponsor

    The stock carburetor has earned my desire to replace it. The engine seems to run out of air at about max torque, it certainly does not like to rev and it coughed at exactly the correct point to get me killed. One of the first choices to come to mind is the Carter side draft with the moniker of "YH". My initial efforts have determined the most common size is 1 11/16" bbl. The Alpine intake manifold throat is 1 1/2", opening up to something more like 1 5/8". Would this mismatch be a problem? I can probably bore it out if necessary. Any info on the flow capability of the 150? I have seen two ratings on the YH, 195 and 128. Which is correct? Is either correct?

    Any ideas on a better carb?

    Bill
     
  2. 260Alpine

    260Alpine Silver Level Sponsor

  3. Bill Blue

    Bill Blue Platinum Level Sponsor

    I'm guessing the MGB's use two of the Harley carbs. My engine has an iron head and a single side draft carb. So I suppose the question becomes "Is a single Harley carb better than a single 150?"

    Bill
     
  4. Bill Blue

    Bill Blue Platinum Level Sponsor

    Looks like the answer to my question is "Probably". The bikes this carb is listed for for were factory rated at 93 hp!

    Bill
     
  5. husky drvr

    husky drvr Platinum Level Sponsor

    Bill,

    The obvious question is about the oil in the top of the carb, how full and how thick?

    If you are considering a change, I would have thought you would try a different route than a MC carb. Then again, you did play with a Fish carb.

    As to your question about Z-S CD150 CFM's, I'm not sure they were ever described in that manner. The CD's were always oversize by flow capacity. The variable venturi is used to maintain a "Constant Depression" in relation to the engine's flow demand. If you are estimating flow CFM by the size of the throttle bore, which is 1.50 inches as compared to a Rochester single down draft carb with 1 7/16 throttle bore and 1 7/32 venturi, the Rochester is rated 160 CFM.

    You might get a better estimate of need by using a vacuum gauge and calculating flow from vacuum and rpm CFM requirements.

    Keep us posted on what you try, please.
     
  6. Bill Blue

    Bill Blue Platinum Level Sponsor

    Don, does MC stand for motor cycle? If so, what is the problem with them? They were used on cycles with displacements close to that of my Alpine. The carb oil issue is another nail in the CD's coffin. Went from overfull to empty (10w30 per owners manual) in about 600 miles. Literally speaking, it seems I can't live with that.

    Bill
     
  7. husky drvr

    husky drvr Platinum Level Sponsor

    Bill,

    Yes, I used MC for motorcycle.

    As for a MC carb, I don't know much about them, specifically. I think most people use them as ITB's (individual throttle bodies), to be a cheaper substitute for a set of Webers, in search for performance. Those would be from something other than a H-D application. I'll admit to not having any interest in or knowledge of H-D's so I must rely on your research and decisions on this subject. I wasn't even aware there is only one carb on a H-D. I do understand your thoughts on potential for the application. I just don't have any information on which to base an opinion, beyond something completely generic.

    I thought you were thinking to build an adapter to mount a ICT or ICH Weber single barrel down draft carb or something on that level. Either way has potential to help someone in the future.

    Don
     
    Last edited: Oct 4, 2021
  8. Bill Blue

    Bill Blue Platinum Level Sponsor

    Why should I spend $200+ on a down draft carb I don't understand (Weber ICH) When I have a perfectly good down draft carb I don't understand (Fish)? Unless someone files a reasonable objection to the MC carb, I think that is the way I'm going to go.

    Bill
     
  9. husky drvr

    husky drvr Platinum Level Sponsor

    Bill,

    No objection. Go for it.

    Just keep us posted on your progress, please? :cool:
     
  10. 260Alpine

    260Alpine Silver Level Sponsor

  11. Barry

    Barry Platinum Level Sponsor

    Bill,

    It seems likely that a carb intended for a "gravity feed" fuel system with a maximum "head height" of about one foot will not need (and may not tolerate) much fuel pressure. FWIW, a one foot head height of "gasoline" is only about 0.33 PSI. Think I would start with no more than 1 PSI fuel pressure at the carb fuel inlet.
     
    Last edited: Oct 4, 2021
  12. 260Alpine

    260Alpine Silver Level Sponsor

    The Mikuni conversions recommend a low pressure fuel pump of 2-4 psi.
     
  13. Bill Blue

    Bill Blue Platinum Level Sponsor

    ORDERED! However, I'm afraid things will slow down considerably. There is a "run" in about three weeks, the last one of the year. I will get serious with the trade out after that. No AFR gauge. In fact, never heard of such a gauge. Are you talking about a tail pipe sensor type of setup? I have a wideband O2 sensor, but it is manifold mounted sort.

    Bill
     
  14. 260Alpine

    260Alpine Silver Level Sponsor

    tailpipe sniffer.jpg Bill, you stick a O2 adapter up the tailpipe connected to the AFR gauge, great for tuning. 14.7 is ideal for emissions but most cars like 13 something idle, around 16 cruise and around 12 full throttle.
     
    Last edited: Oct 4, 2021
  15. RootesRooter

    RootesRooter Platinum Level Sponsor

    Just to be sure, your Coupe should have a single 150 CDSE, not a CD. Does it still have all the smog control lines hooked up?

    My two Coupes had many problems, and the 70hp rating was optimistic, but coughing was never a problem. They always ran smoothly at high rpms.

    It might something as simple as a worn needle jet.
     
  16. rixter

    rixter Gold Level Sponsor

    Yes, should be a 150 CDSE. A version of them had the adjustable needle as opposed to the adjustable jet on the CD. Yet another version had neither an adjustable needle nor an adjustable jet. Not sure what the single carb models use. The two carb GTs used either the 3306 or 3211. If you have the type with neither adjustment, you can get an adjustable jet adaptor from Joe Curto. If you have the type with the adjustable needle, there is an o-ring down the tube where the dash pot top piston rod goes in that seals the tube housing the needle with the ability to adjust up and down a bit. If this o-ring is bad, out goes the dash pot oil. There is a special tool to do the adjustment of the needle with the dash pot cap removed. The tool is a long skinny Allen wrench that turns inside a "holder" that prevents the turning of the air valve while adjusting.

    Rick
     
  17. RootesRooter

    RootesRooter Platinum Level Sponsor

    Sorry, meant needle valve, not needle jet. It's the fuel inlet valve that gets gummed up and doesn't completely close, allowing fuel to push straight thru.
     
  18. Bill Blue

    Bill Blue Platinum Level Sponsor

    The car has a CD 150, as noted by Bob Webb. The car has fewer than 15,000 miles on it, nothing should be worn. The car runs smoothly at higher RPM, just has no power. The coughing occurred at low rpm while pulling hard, trying to accelerate into traffic. The owners manual states that the only carb adjustment is idle speed. It then says it is necessary to adjust the fuel mixture, but does not show or describe how to do so. Total piece of crap (carb) and I see no reason to try to piece it back together. No idea what all the smog control lines would consist of, but nothing appears to be removed or blocked off.

    Bill
     
  19. RootesRooter

    RootesRooter Platinum Level Sponsor

    If its a CD, and not a CDSE, it should have the same adjustments found on a Series V. The later CDSE was meant to have little or no adjustment to keep emissions legal.

    You can switch to a modern, reliable single carb, but it'll still be just that: a single carb. The GT fastback got about 22 more hp with its 2nd carb.
     
  20. Bill Blue

    Bill Blue Platinum Level Sponsor

    I'm hoping to get ten or fifteen of those hp with the motorcycle carb. Some of those 22 have to be due to the aluminum head and better manifold. Seriously, the thing revs like a 50's flathead engine. I figure the engine power falls off at 4000 or so. Yes, it will rev beyond that, but why bother. It could gain 30 hp and still be 30 below the twin carb performance.
    Bill
     

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