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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

    I have driveability, searching for the proper high speed mixture. Tends to be too rich. Looking for the proper combo of air jet and main jet sizes. I have decided the jet terminology is confusing. I think the intermediate jet is in reality a full range jet that gets augmented at high speed, which mean the main is really a high speed auxiliary jet. That is the only way I can make any sense of what I see in the O2 meter.

    Bill
     
    Shannon Boal likes this.
  2. Barry

    Barry Platinum Level Sponsor

    Bill,

    You have actual data (as opposed to conjecture) about how the S&S carb behaves. If the AFR data indicates that the intermediate jet is actually full range and that the main jet is actually a high speed auxiliary, then go down that road and see what happens.

    On a related issue, how did the "vacuum advance port" work out?

    Keep up the good work!
     
  3. Bill Blue

    Bill Blue Platinum Level Sponsor

    Yes, a different perspective on the problem leads to different actions. Currently busy with 3 and 5 y.o. grandkids. Really puts a hold on test drives.

    Have not really looked at the spark curve, but I think the home brew vacuum port is working pretty good. At least I now think of the 1725 as "a hardworking 1725" instead of " a lackadaisical 1725". But I suppose the acid test on the vacuum port is gas mileage, which is going to be hard to determine as the odometer is an off and on again thing.

    Bill
     
  4. Bill Blue

    Bill Blue Platinum Level Sponsor

    Currently have it running pretty good, very responsive up to redline. Seems to be a tad rich in the mower mid range. The current jetting is .060" main (the smallest in the jet jack is .066"), main jet air correction is .066" (comes stock with .040", with instructions to use .060" is the .040 is too small). The intermediate is currently .028". The carb came with a .0265 in the jetting kit, but I drilled it out to .038" doing the initial setup. So I filled that jet with solder and have drilled it to .024". It is now installed but untested. That will occur sometime after we get a nice road desalting shower. Just for fun, I've taken a picture of the tools used to do this. The brass thingy is an intermediate jet. The metering orifice is located in the middle of the jet, close to the threads. The Slivery tool is a pin vise that I used to drill the solder to .024". Just to give everything some size perspective, I've also included a 1/16" drill.

    IMG_8154.JPG
     
    Shannon Boal likes this.
  5. Bill Blue

    Bill Blue Platinum Level Sponsor

    We have recently received a couple of days decent weather with no salt on the roads!! A couple of test rides and jet changes gave us this combination:
    Intermediate jet .026"
    Main jet .056"
    Main Air .078"

    The S&S tuning charts suggest these jets for engines of 100 - 110 cubic inches
    Intermediate jet .031
    Main jet .076"
    Main air .040"

    As you can see, there is no correlation between the suggested size and preferred size. That, along with my idle mixture experience, jet size has little impact on richness and I had to drill out the idle adjustment orifice in order to get reasonable idle richness, makes me wonder what is happening. Lets not even mention the vacuum circuit. Would the fact I'm tuning an even firing four banger and not and not a V Twin make that much difference? BTW, this carb is not a true S&S as it does not carry the S&S logo. Appears to be a very high quality knock off.

    At this time I can say the carb is a huge improvement over the Strom CD. The engine is very responsive and eagerly revs with power up to redline. The performance seems to be close to that of the Series Alpines. I'd like for some guys that are driving good running Alpines to give this car a go and give me their verdict.

    I think the carb looks at home in the car. The finished install uses the stock Alpine accelerator and choke cables, well as the Alpine air cleaner assembly.
    IMG_8187.JPG
     
  6. 260Alpine

    260Alpine Silver Level Sponsor

    Bill, Good job!
     
  7. Barry

    Barry Platinum Level Sponsor



    I think you are on the right track. The average air velocity through the "Harley carb" is the about same for a 10-something cubic inch V-twin and a 10-something cubic inch 4-banger, but the peak velocity is hugely different with the V-twin being about twice that of the 4-banger (two big gulps as opposed to four little swallows). I suspect that a V-twin provides a much stronger or at least different "signal" to the carb than a 4-banger does. If your engine runs well and the AFR's are right, then your jets and air bleed are right.

    Nice looking setup!
     
    Shannon Boal likes this.
  8. Bill Blue

    Bill Blue Platinum Level Sponsor

    Thanks!
    It's amazing how much work goes into such a project. Mating components is the easy part, getting them to work correctly with each other is the hard part. The $&S throttle spring is very stiff and the lever that the accelerator cable attaches to is very short, making for a high effort, short throw, fast acting accelerator pedal. Had to modify the spring and its attaching points as well as modify the Alpine throttle mechanism. Truth be told, made a new mechanism, changing major dimensions. Easy to say, a day each to do. They usually become an exercise of patience and fiddlely, incremental changes as I have no inkling as to the proper changes that have to be made in order to restore what has been lost. But the payoff is a quirk free increase in performance. I think it is safe to say you see only a small part of the project.

    If anyone is thinking of using the S&S carb knock offs, have at it. Given their performance and low cost, it is hard to go wrong if your looking for a side draft set up.

    Bill
     
    Shannon Boal likes this.
  9. Shannon Boal

    Shannon Boal Platinum Level Sponsor

    That is just great, Bill....you have a way of overcoming difficulties!

    I
     
  10. 260Alpine

    260Alpine Silver Level Sponsor

    Bill, How did it perform on your Sunbeam Invasion trip?
     
  11. Bill Blue

    Bill Blue Platinum Level Sponsor

    Ran poorly, but got about 25mpg. I had the car running good, but rich. Leaned out the low speed jet a bit too much for the trip. The interesting thing is that the lean condition would be followed by running rich at about 2,000. Also developed a big throttle sticking problem. But that may have lead to a better tune. While the engine was idling at about 2000, I noticed it was pig rich. Very lean at idle, rich at higher speeds, way before the main jet kicks in. So I adopted a different tuning regimen. Instead of selecting the low speed jet based on throttle closed, "book" tune, I went to a bigger jet and set the idle richness for stoic at 2000. This gives a slightly less than optimum idle, but is okay. It also produces a leaner tune at low speed. The big surprise, it helped the lean condition when at speed and WOT. I settled on a low speed jet that is two sizes larger than I had been using. Runs better, no hesitations, cruises leaner and helps the WOT lean "hole". I then leaned out the main jet. I'm currently two sizes smaller, would like to go even smaller, but the WOT hole got awful. Fiddling with the air bleed. I've found that zero air bleed is not the solution. Installed a jet with my smallest drill size, .023" . Not been able to test it. Will go up by 4-5 thou steps, trying to find the magic size. BTW, my current low speed jet is .0295" and the main jet is .043". Will have to go to .046" if I cannot solve the lean problem. .043 still gives a rich reading, about 850-900mv. .046" produces readings of 900mv+. The size for the trip was .051", very rich. These are level cruise @ 3,000 - 3500.

    Bill
     
  12. Shannon Boal

    Shannon Boal Platinum Level Sponsor

    I wonder if you might do well to start with the main and air correction jets close to the same values. Maybe 0.043" Main with 0.040-0.046" air correction jet. This oughta help with the cruise speed richness (.800-.900 volts, If I recall?)
     
  13. Bill Blue

    Bill Blue Platinum Level Sponsor

    I too wonder, but I've decided to be more methodical. Right now, I'm testing main two fuel jets, .041" and .046". Started with zero air with both jets. Then .024" air. The .045 jet was the winner, no richer, but ran better. Today I'm testing .030" air with the two jets. When I've found the best combo and it includes the .043" jet, I will try that air jet with a smaller main, something in the high 30's. Then, depending on results, I will start enriching the low speed jet. Right now the mains are effective (.9v) down into the teens.

    Bill
     
  14. Shannon Boal

    Shannon Boal Platinum Level Sponsor

    Methodical, yes, change one thing at a time, increments of ten percent or less......air correction jet causes mixture leaning with speed increase. At one point, when maybe it is equal in size to main jet, it will lean out slightly as it winds out. If it is too small, you'll blow black smoke, or blacken the plugs. Never saw what happens if it is too large. You are fixing to write the book on this thing, and I can't wait to read that book!
     
  15. Bill Blue

    Bill Blue Platinum Level Sponsor

    I guess the title of my book would be "Tuning an untunable engine". It runs rich at low loads and lean at high loads and I was not able to do much to change that fact. Going up in air jet soon revealed the .041" jet to be too small. So it was dropped out of the test and replaced with an .052". The first run was vastly superior to any run the .046" jet had. No richer at cruise, but did not fall off as much at load. So the day suddenly changed to finding the optimum air jest size. Worked the air jet for the .052" jet from .030" up to .052". In a word, all of them sucked, some not as bad as others. Finally settled on .037". The stupid thing still runs rich at cruise (.8-.9+ mv.) and lean (.045 mv.) under load. Hit the gas at 2,000 rpm and it goes to .06, dropping to .045 at higher rpm. I downshifted at the bottom of a hill and wound it up pretty good going up the hill in 3rd. I would guess at least 5,000 rpm. Dropped to .05 mv. and stayed there. Maybe would have dropped a bit more, but I decided I had seen enough and let off.

    I have concluded the problem is the design of the single barrel carb. As the throttle is opened, the air flow past the main jet opening slows and so does fuel flow. What I do not understand is why the flow does not go up as engine speed increases. The carb is rated for engines from 1.3 up to 2 liters, so an Alpine winding out should pull some serious air, but it doesn't seem to be enough. Maybe I'll keep it to use as a throttle body for a MicroSquirt. If we decide to keep the car, that is probably what will happen. In the meantime, the car is very drivable and peppy as long as you keep your foot off the floorboard. Maybe a throttle stop on the carb to prevent overcarburetion?

    Bill
     
  16. 260Alpine

    260Alpine Silver Level Sponsor

  17. Bill Blue

    Bill Blue Platinum Level Sponsor

    I'm finding it hard to relate to my situation and my curiosity level is low. Everything I read is about power, nothing about driveability or economy. Also, I'm tired of fooling with the contraption.

    Bill
     
  18. Bill Blue

    Bill Blue Platinum Level Sponsor

    One of my biggest problems has been the main jet kicking in way too low. So I just removed the .037" air jet and replaced it with .072". Maybe that will separate things. We shall see. If the intermediate jet is good for 2500 rpm the main will be also. That would give carburetion up to 5,000
    on top of the intermediate.
    Bill
     
  19. Bill Blue

    Bill Blue Platinum Level Sponsor

    Well that was somewhat of a bust. Dropped the cruise richness 20-30 mv. Still idles along at ,9mv in 3rd gear. What small amount of time it seemed to be running on the intermediate jet, I saw readings in 200's. So I'll go to the next larger intermediate, drill out the air jet to about .080" and continue from there.
    Bill
     
  20. husky drvr

    husky drvr Platinum Level Sponsor

    Bill,

    Just a thought, any chance your air filter mount is affecting the bowl vent?

    Since this thread is about your coupe,I'm also going to include a suggestion about your search for a fifth gear. The quickest, simplest way for you to have another gear is for you to contact Jeff in the UK about the availability of an Arrow range gear box with a J-type OD.

    Just thinking,
     

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