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Running rich or not couriosity

Discussion in '"Stock" Alpine' started by Acollin, Sep 8, 2020.

  1. Acollin

    Acollin Donation Time

    1966 sunbeam alpine - stock set up

    my car runs great for the most part, but it runs better still when I pull the choke out just a bit. Without the additional choke, it might bog down when hitting the throttle - going up a hill. It then seems to run flawlessly with the additional choke.

    Having to pull the choke out suggested to me that I was running a little lean. So I thought I should back the jet off / down a little. Before doing so, I pulled the plugs today and all four were uniformly dark with carbon. This suggests to me that I have been running rich- the blackened plugs.

    Am I running rich or lean?
    Is this a problem that can be cured by doing something other than raising or lowering the jets?

    Thanks all
  2. alpine_64

    alpine_64 Donation Time

    I know you say stock.. But are you running the stock 150CD stromberg carbs or have you gone to a single weber, this makes a difference to the answer.

    (sorry to ask but many people consider the motor stock even wirh a carb swap)

    As for the general assesment of plugs.. If they are a dry dark sooty colour thats a rich mixture.
  3. Acollin

    Acollin Donation Time

    My car is pretty close to stock. I’d say really close to stock
    I am running CD 150s. No need to apologize— I appreciate any and all questions— especially if oddities can be fixed or at best understood.
    Thanks for the question
  4. belmateo

    belmateo Gold Level Sponsor

    My experience with these carbs is lean running rather than a rich mixture.
  5. Acollin

    Acollin Donation Time


    Are you suggesting I raise the jet? Leaning the mixture.
    Can you explain how by adding some choke I run better?
  6. belmateo

    belmateo Gold Level Sponsor

    If it is truly a lean mixture, you applying the choke correction proves that. What temperature are you at when this is happening? I had the same experience with my Alpine until it was fully warmed up.
  7. alpine_64

    alpine_64 Donation Time

    A few more questions.. Also a side note i have limited personal experience with 150CD ... But years if reading about peoples issues on the forum.

    The carbs from my understanding take a while to get settled to a fully warm motor, so people apparently run with chocke for a little while as everything gets to temp.

    You say the car bogs down a little when you hit the throttle, the CD stands for constant draft which normally means they get good throttle response.. So id say that the bog down is likely an over fuelling condition.

    If the diaphrams were bad it would run poorly same with a vac leak.. You dont seem to have that issue... The rich plugs may be a result of you playing with the choke.. Clean the plugs and drive it for a bit without using choke and see if you get a nice clean plug after a run.

    Maybe adjusting the linkage and needles per the WSM might be a place to start to see if that resolves the plugs if they still show sooting.

    Also.. Assume you are not having any backfires?
    Have you checked your timing?
  8. hartmandm

    hartmandm Moderator Platinum Level Sponsor

    Post a picture of the plugs, if you have it.

    Your description sounds like mine - and I was running lean. Ran better with some choke. Would stumble during acceleration.

    Do you have the original needles - 5M? Based on other threads on this forum, I ended up switching to "richer" needles. It was a big improvement.

    How many turns out are you?

  9. Filister

    Filister Silver Level Sponsor

    Have you checked the oil in the dampers? This serves the same function as an accelerator pump and if not working can cause a bog when you step on the gas.
    belmateo and beamdream like this.
  10. beamdream

    beamdream Gold Level Sponsor

    Yes you can have rich or lean stumbles when accelerating, black plugs are indicative of rich running but the question is; are you causing it with the choke?

    As mentioned above, the damper oil is a factor when accelerating, without it the piston rises rapidly to top of it's travel and the net result is an over fuelling situation until the vacuum chamber stabilises, so do check the damper oil.

    The other thing to check with CDs is the piston freedom, do you get a nice sharp "click" noise when you lift and drop the piston ? If the needle is binding in the jet then you'll be permanently rich at low revs.
  11. Acollin

    Acollin Donation Time

    I do not have any pictures of the carboned up plugs as I cleaned them up yesterday and was unable to take a drive. I do not know how many turn out I am at this point, but when I cleaned the plugs I also raised the jet a quarter turn. I will check the oil level in the carbs today. Needles are not binding - each moves freely and clicks with the lift pin. I can not recall which needles I am running as it has been a while— not all that many miles— since the carbs were apart.

    I think I answered all questions— will hopefully take a drive today —- although we are dealing with a wildfire crisis here in Oregon and while I live near a rain forest in Clackamas County, we are under an alert in the whole county. We are fine at this point, but there is genuine suffering Not all that far off.

    be well all and thanks for your thinking
  12. spmdr

    spmdr Donation Time

    Just because I didn't see anyone mention it, you may want to check for ware on the "main jet"(s).

    One would tend to adjust it for a correct mixture at idle/low throttle and have it run rich in other ranges.

    The point is check for worn parts.

    Also check the float levels and fuel flow.

    a Wide band O2 sensor would reveal the mysteries.

    Jarid may reveal more Carb tuning tips.
  13. rixter

    rixter Platinum Level Sponsor

    My understanding of the dashpot is that if the piston rises too quickly on acceleration due to low or too thin oil, a lean condition results. The analogy to an accelerator pump is because such pumps inject extra fuel during the sharp acceleration condition. Rich or lean carb operation under other circumstances is different and can have several causes as others mentioned. The choke could be pulled out to at least partially overcome a lean condition on acceleration as a result of low or thin dashpot oil, but it would also provide a richer condition across the spectrum. Acollin posts that the issue is most troublesome when hitting the throttle. That to me points in the direction of the dashpots.

  14. Alpine 1789

    Alpine 1789 SAOCA President Platinum Level Sponsor

    Stay safe!
  15. RootesRacer

    RootesRacer Donation Time

    If the choke pull yields more power than I am inclined to think it (the engine) wants more fuel.
    CD stands for constant depression (Michael) and the theory is that the airflow will be restricted by the piston, which forms a variable venturi which holds a constant depression (vacuum) on the volume between the throttle and the piston.
    I would lower the main jets, which increases the main jet cross section which WILL make the engine run richer at the same volume flow.
    Things to be wary of though are that if it tends to run lean near idle and not as much at higher loads then most likely your trouble is warn spindle shafts or a vacuum leak somewhere.
    Factory adjustment says to adjust the main jets for best idle and lift the pistons by hand to make sure the idle speed drops as opposed to increasing speed which indicates an excessively rich condition. The trouble is you can on;y change the running condition at one operating point, not at idle and at power like on a conventional carburetor.

    Watch your plugs to make sure that your main jets are balanced.

    The dampers and oil viscosity should not effect the static air fuel ratio. It does act like an accelerator pump on a conventional carb in it causes the pistons movement to be resisted in the opening direction (due to increase in throttle opening). This causes a momentary increase in throttle vacuum which increases fuel delivery until the piston has reached the position where the throttle vacuum is again at its control point.

    God I hate Strombergs...
  16. hartmandm

    hartmandm Moderator Platinum Level Sponsor

  17. alpine_64

    alpine_64 Donation Time

  18. RootesRooter

    RootesRooter Platinum Level Sponsor

    If your carbs are high mileage and never been completely rebuilt, then the throttle shafts are likely worn and allowing vacuum leaks, which causes the carbs to run rich. In that situation, you can turn the adjustment screws almost all the way tight and still run too rich.

    Do you need extra choke just on hills, or when accelerating on flat ground as well?

    Are your carbs synched?
  19. beamdream

    beamdream Gold Level Sponsor

    Yes indeed, lack of damper oil will induce lean mixture under acceleration, my apologies, brain fade on my part.
  20. Acollin

    Acollin Donation Time

    Have not gotten to the shop and air quality is poor at best. Night fell unexpectedly way before sunset/ very eerie — So I have not done any more investigating. If we get the Level 3 notification, its Leave home and don’t look back. Think wishful thoughts for my cars. Wind direction is helpful to us today, but not the kind of thing you want to bet your life on.

    running up hill and on the flat was possible— you could feel the car wanted to do better—-it just ran much better with a little choke. The carbs were balanced recently ( the listen through a hose method)— which I found very helpful/revealing even though not very modern. The carbs have not been taken completely apart in my my time with the car. I bought my car from a California gentleman over 90 years old who owned the car from the late 60s. If he rebuilt the carbs , it had to be long ago. That said, my guess is that the car did not have a lot of use in the last 40 years.

    i will update if I can get some shop time and things do not go upside down for us. Oregon has trouble from California to Washington and as many of you know there is fire trouble enough For many.

    be well all

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