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Adjusting stromberg cd 150s

Discussion in '"Stock" Alpine' started by Acollin, Jun 21, 2014.

  1. Acollin

    Acollin Donation Time

    1966 Series V

    I did the initial set up from my owners manual.

    Slow running screws two turns in
    Jet adjusting "screws" two and a quarter turns out

    The car was on what I would call a fast idle -- 2500 on the tach once warmed up.

    I did not lower/raise the jet adjusting screws because i was not exactly sure which way to go and how far to go. I reached a comfortable idle by turning the slow running screws out until I hit about 1000 rpm.

    I had to leave it -- going back in today. My assuption is, based primarily on smell, that i am running rich and the jets adjuster needs to,be screwed in some and my slow running adjusters need to screwed back in some( i came out 1.5 turns). I will pull a plug and expect carboned up.

    Please advise: should I go back to book set up and try to find steady rpm of 1000 with the jet adjuster? If I can, do I simply leave the slow running screws in at 2.25?

    Any advice will be appreciated.
  2. RootesRooter

    RootesRooter Platinum Level Sponsor

    Have you synchronized them with a unisyn yet? You'll never get close to correct idle if they're out of balance.
  3. Acollin

    Acollin Donation Time

    I may have taken a few steps backward.

    I had it running not great,but it was driving-- . I began to "fiddle" more intently and now I can't get back to where I was.

    The front carb had a weaker hiss. I put my hand over the air intake and little changed. I put my hand over the intake on the rear carb and the whole thing shut down-- totally "strangled". I believe I was only running on the one carb-rear.

    My "fiddleing": the pistons are not moving the same ( a hitch in the front) and now when I tighten down the top screws on the front carb, the piston does not move at all. I tried the "centering " procedure, but when I tighten those top screws all locks up on the front carb.

    A very frustrating day-- i went from driving on my property, to a carb that I know is now messed up.

    Please advise!!!!
  4. RootesRacer

    RootesRacer Donation Time

    Have you performed the "jet centralization procedure"

    The main jets on a CD150 can impede the needles and cause the pistons
    to hang up.

    Step 1 do jet centralization procedure. Be sure the pistons pass the "drop test".

    Step 2 put the main jet on both sides to the same, known position according the factory instructions (2.25 T out?).

    Step 3 adjust throttle stop (a bit more open than usual to help starting).

    Step 4 Be sure the throttles are more or less rough synchronized (you will fine sync them later).

    Step 5 Start the car, set idle speed (Lowest speed it will run at, at or above 750rpm).

    Step 6 adjust the main mixture screws the EXACT same amount on each carb until you get a quality idle at 750 RPM. Return to step 5 if needed.
    You may reach in and gently lift the piston a small distance on each carb to cause a "lean" condition to gauge if that carb is running lean or rich.
    If the lift doesnt quickly cause drop in RPM, you are probably rich and will screw that ONE carbs main jet UP/IN.
    You may temporarily adjust the jet DOWN/OUT to richen that carb, if the idle speed goes up, it likes what you did.

    Step 7 with a flowmeter, stethoscope or small rubber hose, adjust synchronization of the front to rear carb. Flowmeter will read the same level
    OR the steth/hose will have a similar hiss when sync is achieved.
    Return to step 5 if needed.

    Continue till you achieve a quality idle, flow is synched and each carb responds the same to lifting the pistons a tiny distance.

    If after doing this and getting a good idle, the engine doesnt run great under power, you have a vacuum leak or your throttle shafts are worn out.
    The main jet adjustment at idle should also be what the engine needs in general.
  5. Acollin

    Acollin Donation Time

    Ah Haaaa!

    I just spent a bunch of time working on my front carb. I could not for the life of me get it to act as the manual wants----the piston was still hanging up.

    I was getting a bit frustrated--Until some old wise words came back to me: "just because your parts are new does not mean they are good".

    I purchased a pair of new needles. I only used one-- on the front carb.They came wrapped in plastic with a paper label stating the proper designation-- 5m. The needle that i removed from my front carb was stamped,on the end, 5m.

    I went back to the old needle and things are now working as they should.

    Are my new needles the wrong size? Do they need to be taken down with emory-cloth? Is this a common story? I replaced the jet , some o rings and some washers from a new kit I got from the previous owner. So it is that even new parts seem to compliment my old needles.

    Whats up here?-- please comment!
  6. RootesRacer

    RootesRacer Donation Time

    Dont sand on the needles, they are chrome plated.

  7. Acollin

    Acollin Donation Time

    Yes-- i followed the centralizing procedure in the "light car range" book-- about 5 times --- believing that my parts were new and in good working order. I was meticulous in following the steps of the centralizing procedure. Even if I did it incorrectly a few times, there is no way i messed it up five times in a row. It worked fine with my old needle--but NOT the new needle. The piston would not pass the drop test with the new needle inserted. The piston drops fine with the old needle inserted.

    I believe I either got a new wrong needle( incorrectly labeled) or a poorly manufactured needle. Has this ever happened to you?---- A new part not working as expected.

    I will get to the shed today and see how the new needle interacts with my old jet-- both pieces are now out of the car. I am guessing the needle will bind in the orifice.

    Are my new needles junk?
    Thanks for all the help
  8. RootesRacer

    RootesRacer Donation Time

    Lots of new parts available today were yesterdays rejects, returns and quality problems. I dont discount that your needles are NFG, but you should be able to let them roll down an incline and see a bend to the needle.
    A messed up taper profile will not cause the problem you have, only a bent needle or non centered main jet.
    As for if you think the taper is not correct, taking measurements with a caliper on known intervals and comparing will let you know if thats the case.

    Tell me about your centralization procedure.
    Did you replace the diaphagms, did you loosen the top cover screws then retighten with the piston all the way down and the jet all the way up.
    Tighten the cover screws a little at a time cross tightening like if it was a cyl head.

    If done right, the centralization proc will put the jets center absolutely centered to thick section of the needle. You will know right then and there
    if it didnt work out becuase the piston will hang near the bottom of the stroke. Try try again till you can drop the piston and it "clicks".
    If it hangs up a little and you cant seem to get it perfect, it may be good enough, more on that in a bit.

    As for centralizing the jets, I find its a progressive process, getting closer and closer the more times you perform it.
    Start with the jet retainer nut looser (jet of course as high as it goes) and rap gently on the adjustment screw to wiggle the jet to the needle center.
    Drop the piston a few times, then tighten the jet retaining nut ever so little.
    Repeat until you its all tight and you pass the "click" test.
    When its centered, it may hang just a little towards the end of the pistons stroke, remember when you lower the jet to running clearances the jet will have better clearance and should no longer rub.

    Do it all again till it works out.
  9. Acollin

    Acollin Donation Time


    Well, the new needle did NOT bind in the old jet -- so my theory goes out the window.

    My belief now is that " rootesracer" must be correct and I never did get the jet centered on the needle. When I changed things out I probably lucked into centering the jet as i did not have the tips that rootesracer provided when I headed out to try again: wiggle the jet-- make certain the piston is at its lowest-- more than 3 flat faces. None of this great advice-- while truly logical is not stated in anything I read.

    It is running really well now, but I truly lucked into the centering as opposed to following the correct path. A friend of mine who plays golf always says he would "rather be lucky than good" and "even a blind squirrel will occasionally find the nut". It seems like both of these old quips applies to my carb work.

    Curiosity:What would bind if the top screws were not eased down systematically? I cannot see how that might change the centering process.

    Thanks again for the consistent and reliable help. Your experience is worth a great deal to all who wish to learn.

    I have a bit of a leak in the rear carb so, I'll be going back in.
    Also: Should I assume that when I put the air cleaners back on my my outstanding carb work will require new mixture settings?
    I suspect less air will be available at intake and the mixture will then be a bit rich.

    Thanks again
  10. RootesRacer

    RootesRacer Donation Time

    Why would it? The jet is a hole and the needle a taper.
    The two come together where the taper diam matches the hole diameter.
    Since the taper is hard a$$ed material and the jet is brass, the jet will not
    stick to the needle, it will deform if need be.

    The top cover is pushed away from the case by the springiness of the diaphragm elastomer. If you tighten one corner abruptly, the rubber on the opposite side pushes against it and the top cover can "tweak", taking a permanent shift in squareness. Also depending on the tightness of the top cover to its machined index ring in the case, you can bind the two parts together and end up raising the flat surface, which makes the two parts no longer parallel.

    When you say you are leaking now, is it leaking out the bottom (jet assy)?

    There are o-rings in there that need replaced more often than the diaphragms do. They take a thermal set, then one day you adjust the main jet and the o-ring begins to leak.

    I would remove the hole jet assy and make certain that its clean enough and smooth enough for the loosened main jet to be able to move laterally when the jet retainer nut is loosened. If it can't move, you will never get it centered.
    I also like to center the jet with the carbs off the intake. Its pretty easy to install and remove stroms from the SV intake and then you can see down the jet assy on the bench to eyeball them into a close starting position.

    I am one of the few people you will find on this board that actually likes stroms. Variable venturi carbs are a better fueling concept than std venturi carbs, many OEMs were beginning to go VV prior to the advent of fuel injection since VV yields best fuel control under lighter loads, an area that std carbs are the worst at.


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