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Thread: Carb questions

  1. #1
    Big Inch
    Hopefully someone can help me out or at least get me a little closer. I recently had my motor rebuilt and since then I have not been able to get the carb dialed in. I keep burning up plugs. I have an 1150 dominator and the air bleeds are turned out only about 7/8's turn. This keeps the transom fairly clean but the plugs are still fouling. This weekend I pulled the air bleeds to blast them clean and noticed that 1 of the idle air bleeds is a much larger size then the rest. This motor was originally built and tuned on the dyno. Does anyone see this as something that may have been done during the tuning or was it a mistake that has been causing me tons of grief ever since? Second question is in regards to jetting. This carb has mechanical secondaries and no power valve in it. Should I be running it square because of this? Because I'm not.

  2. #2
    cfm
    When you say 'idle bleeds' do you mean the idle mixture screws by any chance ? Is the large one you mention knurled so you can turn with your fingers ? If so, this is probably a BG one.
    If you have no primary or secondary PV then jetting usually ends up square.
    Was this the same carb you had before engine rebuilt ? Is it box stock or did someone modify it for you ? If modified - by whom ? If a good place then have them set this up for you.
    Also, depending on compression, cam, etc,etc will depend on how much initial advance you need. Initial advance plays a huge role in not only how the engine idles but also how well the carb can do it's thing.

  3. #3
    cfm
    When you say 'idle bleeds' do you mean the idle mixture screws by any chance ? Is the large one you mention knurled so you can turn with your fingers ? If so, this is probably a BG one.
    If you have no primary or secondary PV then jetting usually ends up square.
    Was this the same carb you had before engine rebuilt ? Is it box stock or did someone modify it for you ? If modified - by whom ? If a good place then have them set this up for you.
    Also, depending on compression, cam, etc,etc will depend on how much initial advance you need. Initial advance plays a huge role in not only how the engine idles but also how well the carb can do it's thing.

  4. #4
    Big Inch
    When you say 'idle bleeds' do you mean the idle mixture screws by any chance ? Is the large one you mention knurled so you can turn with your fingers ? If so, this is probably a BG one.
    If you have no primary or secondary PV then jetting usually ends up square.
    Was this the same carb you had before engine rebuilt ? Is it box stock or did someone modify it for you ? If modified - by whom ? If a good place then have them set this up for you.
    Also, depending on compression, cam, etc,etc will depend on how much initial advance you need. Initial advance plays a huge role in not only how the engine idles but also how well the carb can do it's thing.
    I'm not referring to the idle mixture screws I am referring to the adjustable air bleeds for the three circuit metering. 1 is much larger then the rest and I'm just curious if anyone thinks their might be some reason for this. The motor was originally built by Pro marine in Havasu and was dyno tuned so I'd have to assume that he made this adjustment while tuning it on the dyno. The thing has always burned plugs idling though and I'm wondering if maybe this is the reason why. I would take it back to him except that it was built some time ago and I'm sure he won't recall exactly what and why the mods were done at the time.
    As far as the timing goes it was originally set up with like 10 initial and 34 total advance but when it was rebuilt the guys that did the work put in a new distributor and locked it out at 34 saying that this is how they would run it and they are very reputable.
    They did go with me to lake test it and dialed in the idle circuits and gave it a quick run but this was out at Castaic at like 8 in the morning on a cool day and since then it's only been run out in Havasu.
    Cfm would you recommend that I make the jetting square on this and adjust from there?

  5. #5
    cfm
    I have an 1150 dominator and the air bleeds are turned out only about 7/8's turn. This keeps the transom fairly clean but the plugs are still fouling.
    I am referring to the adjustable air bleeds for the three circuit metering.
    I guess I am having trouble with your wording. Or my understanding. LOL.
    Turns in or out with air bleeds ? Adjustable air bleeds ?
    I've only known replaceable air bleeds that screw in. Like fuel jets, you turn them into until seated. Never heard of one's you turn in/out to adjust like you would the idle mixture screws. Maybe I'm lost or just don't know of adjustable air bleeds that you adjust by screwing in or out.
    Please unlose me. I'm so confused.
    =========================
    I'm not that into locked out timing but many are and like it. Typically people that lock out the timing have cam in the 250° and higher duration at .050".
    =========================
    BTW: I do not have any tuning knowledge really with three circuit Dominators. I do know that they can give you major fits if not set up right. In my case, if I had a Dom it would go out to a company like Nickerson's that set up hp marine carbs daily.

  6. #6
    steelcomp
    I'm a little lost here, as well, with the "turning" of airbleeds. Airbleeds are like jets, and come in different sizes, but they need to be tight.
    You have four idle air bleeds, one for each venturi. Are you saying that one of the four is much larger? Typically with a three circuit carb, the intermediate air bleed (the one in the middle) is going to be the large one...significantly larger than the other two. Maybe someone got the airbleeds mixed up? I'd get ahold of the Holley tech line and find out what the stock jetting and air bleeds for that carb are and start from there. 99% of the time those carbs will work pretty well right out of the box, and only need some fine tuning. With a single carb and no PV's, you should be very close to square on the jetting.
    One more note...the carbs with intermediate circuits can be really fat at part throttle. If you spend a lot of time cruising at part throttle, you might have to work on that circuit, or get a carb without one.

  7. #7
    Big Inch
    I guess I am having trouble with your wording. Or my understanding. LOL.
    Turns in or out with air bleeds ? Adjustable air bleeds ?
    I've only known replaceable air bleeds that screw in. Like fuel jets, you turn them into until seated. Never heard of one's you turn in/out to adjust like you would the idle mixture screws. Maybe I'm lost or just don't know of adjustable air bleeds that you adjust by screwing in or out.
    Please unlose me. I'm so confused.
    =========================
    I'm not that into locked out timing but many are and like it. Typically people that lock out the timing have cam in the 250° and higher duration at .050".
    =========================
    BTW: I do not have any tuning knowledge really with three circuit Dominators. I do know that they can give you major fits if not set up right. In my case, if I had a Dom it would go out to a company like Nickerson's that set up hp marine carbs daily.
    Aww sorry now I see where the confusion is. My fault. Ok first of all when I said my air bleeds are 7/8 out I meant my idle air/fuel mixture screws. The reason I posted this is because my understanding is that if your idle mixture screws are not out at least a full turn then there is a problem. I was just making a statement of this as another indication of a possible problem but my wording was messed up in my description and I did not complete my thoughts on it. Ok since my idle mixture screws are out less then a complete turn and I'm still burning up plugs idling around I'm trying to figure out why. If I turn them in more it seems to lean out at idle as the motor will surge occasionally while idling in gear. Usually only does this in the morning while motor is cold but after it warms up it will generally idle really high like 11-1200 instead of 900. Regardless of this it is still burning plugs.
    Ok so when I was referring to the adjustable air bleed. I am referring to the air bleeds for the three circuit metering. The allen screws that you referred to. By adjustable I mean they can be removed and drilled out to different sizes to adjust your fuel curve. On the idle circuit there are 3 with less then pin hole sized orifices and 1 that is much larger. If I had to guess I'd say like a 3/32 drill size or so maybe even 1/4. I'm assuming this was done when the motor was new and was tuned on the dyno by the engine builder. Maybe this is a common practice in carb tuning and has it's benefits or maybe this makes it hard to keep the motor from burning plugs and if so I'd like to know lol. Just curious what your thoughts are on this mod because if it is a problem I'd like to change it out and put it back to stock.
    Hope this helps

  8. #8
    Big Inch
    I'm a little lost here, as well, with the "turning" of airbleeds. Airbleeds are like jets, and come in different sizes, but they need to be tight.
    You have four idle air bleeds, one for each venturi. Are you saying that one of the four is much larger? Typically with a three circuit carb, the intermediate air bleed (the one in the middle) is going to be the large one...significantly larger than the other two. Maybe someone got the airbleeds mixed up? I'd get ahold of the Holley tech line and find out what the stock jetting and air bleeds for that carb are and start from there. 99% of the time those carbs will work pretty well right out of the box, and only need some fine tuning. With a single carb and no PV's, you should be very close to square on the jetting.
    One more note...the carbs with intermediate circuits can be really fat at part throttle. If you spend a lot of time cruising at part throttle, you might have to work on that circuit, or get a carb without one.
    I hope my last post cleared up the confusion. What I highlighted in red in your post is exactly what I'm concerned with.

  9. #9
    steelcomp
    I don't know anything about having less than one turn with the idle screws being a problem. Usually it's a problem if they have no effect, but it sounds like yours are working.
    You have a big problem if one idle air bleed is that much bigger than the rest. As I posted above, look at the middle bleed on the other three venturies in the carb. They should be the larger of the three.
    Is it possible that someone has gotten the large one out of place on that one venturi?
    Other than that, are all the air bleed circuits the same size, ie: all four high speed the same, all four intermediate the same, and only the one idle is large? If so, I believe that's your problem.

  10. #10
    Big Inch
    I don't know anything about having less than one turn with the idle screws being a problem. Usually it's a problem if they have no effect, but it sounds like yours are working.
    You have a big problem if one idle air bleed is that much bigger than the rest. As I posted above, look at the middle bleed on the other three venturies in the carb. They should be the larger of the three.
    Is it possible that someone has gotten the large one out of place on that one venturi?
    Other than that, are all the air bleed circuits the same size, ie: all four high speed the same, all four intermediate the same, and only the one idle is large? If so, I believe that's your problem.
    All the rest are the same. The high speed circuits are fairly small and all the same. The middle bleed are like you said larger and all the same. The idle air bleeds are all extremely small except for one which is actually larger then even the middle circuits.

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