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  1. #16
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    Quote Originally Posted by GtoGeoff View Post
    You see, you are not understanding the relationship. The above test will take 5 min, & you will learn something....

    I run 48* of initial timing with my engine. Yes, 48*!! It is done with initial + vac adv added via manifold vacuum.

    An engine I tune for drag racing needed 53* at idle with the big cam it had in it. Probably would have stalled with less than 20*.....

    David Vizard. Author of 30+ automotive books, uni lecturer on motorsports, consultant to car companies, F1 teams etc, says this in his Holley carb book:

    " The optimum idle advance for a short cammed street engine is typically 35-40* & [ though not typically realised ] as much as 50* for a street/strip engine."
    Think about why timing at idle is mentioned in a carb book....

    Also, below, scroll down to post #6,

    http://www.hotrodders.com/forum/vacu...bad-47495.html
    Seriously? So your timing retards as RPM’s and torque builds? I would think a big cam motor at 53 degrees would turn the carb into an exhaust pipe. Or flame thrower. And theee is no point running a vac advance off manifold vacuum. Unless you are using it as a timing retard as soon as you open the throttle. But a big cam motor won’t pull enough vacuum to activate it anyway.
    Last edited by Castiron355; 16-01-2019 at 10:48 PM.

  2. #17
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    Bfhoon. I feel your compression is showing signs of a tired engine. The plugs do look a little wet. A single plane and low compression probably isn’t providing enough turbulence for a complete burn.

  3. #18
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    hi
    Do a wet compression test . Crank each cylinder same amount . This will tell u where the compression is going . 2 squirts in each cylinder and crank 8 times each cylinder .
    If compression comes up rings are leaking if not valves leaking .
    Warm engine get rid of smoke.
    Let cool
    Leak down test each cylinder . each cylinder must be on compression stroke . Around less than 5% is good . Over 10% is poor sealing .


    Fix any cylinder that tests poorly first . Tunning can only cover up poor condition so much .

  4. #19
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    BFHOON as youve been told before the idle circuit is way to rich.

    no amount of plugs timing etc is going to fix an idle circuit thats way to rich. if the mixture screws are only half turn out its to rich. 1 to 1.5 is about the avg for good clean running.

    the carb would need some rework to fix this. how much depends if the idle jet is fixed or is a screw in type
    11 second E85 bottle fed boat anchor

  5. #20
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    Quote Originally Posted by EVL253 View Post
    BFHOON as youve been told before the idle circuit is way to rich.


    no amount of plugs timing etc is going to fix an idle circuit thats way to rich. if the mixture screws are only half turn out its to rich. 1 to 1.5 is about the avg for good clean running.

    the carb would need some rework to fix this. how much depends if the idle jet is fixed or is a screw in type
    Yep x2

    If the correct idle tune is only 1/2 turn out of the idle mixture screws, it indicates that the transfer circuit tune is pig rich.


    If the IFR's (idle fuel restrictors / 'transition circuit jets') were reduced in size to achieve the correct transition circuit AFR, likely the idle mixture screws would need to be wound out 1 to 1.5 turns to supply enough/correct fuel at idle.



    More timing, hotter plugs, smaller mains jets, driving around with the tongue poking out the corner of your mouth, is not going to keep the plugs clean if the idle fuel/'transition circuit jets' are too large and creating a rich T circuit cruise.

    It could be that with the screws out only 1/2 a turn the idle tune is correct, the main jets are the correct size, the PV and PVCR are the correct size . . . but if the transition circuit is rich/IFR too large, when you are driving around at 60kmph in/on the transition circuit, you are probably high 11:1 low 12:1 AFR and fouling plugs.

  6. #21
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    Hooked up the afr guage and at idle im getting about 14.3 to 14.5 not much fuel smell now when i was driving it before it was actually cleaning a tiny bit of the carbon off the porcelian. I might try some new plugs and see how it goes seems to be idling ok now

  7. #22
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    The OP's carb is a universal type and has fixed iab's and ifr's. The transition slot is probably too big for the engine too.

    Only adjustments i see are main jets, pv and 4 corner mix screws.

    The comp' results are all over the shop and you are fighting a losing battle trying to tune correctly, as mentioned in older threads.

  8. #23
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    Quote Originally Posted by GtoGeoff View Post
    You see, you are not understanding the relationship. The above test will take 5 min, & you will learn something....

    I run 48* of initial timing with my engine. Yes, 48*!! It is done with initial + vac adv added via manifold vacuum.

    An engine I tune for drag racing needed 53* at idle with the big cam it had in it. Probably would have stalled with less than 20*.....

    David Vizard. Author of 30+ automotive books, uni lecturer on motorsports, consultant to car companies, F1 teams etc, says this in his Holley carb book:

    " The optimum idle advance for a short cammed street engine is typically 35-40* & [ though not typically realised ] as much as 50* for a street/strip engine."
    Think about why timing at idle is mentioned in a carb book....

    Also, below, scroll down to post #6,

    http://www.hotrodders.com/forum/vacu...bad-47495.html
    If it had been locked at 36-38* it probably would have idled and ran better...

  9. #24
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    So I put in one new spark plug for tuning purposes and gave the car a good 5kilometre run. The porcelain didnt foul at all but now im thinking its lean check out the new spark plug is this just a sympton of it being new? I noticed to that the idle rpm slightly increased so maybe if I replace the other 7 I will be able to adjust my idle down on the curb idle.
    Any guesses what timing im running ? IMG_0184.JPGIMG_0183.JPGIMG_0182.JPG

  10. #25
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    EH179,
    You are pretty close, you get half a cigar.... I am using locked timing, 35* & a sizeable cam. It idles better with the extra 13* of timing at idle, which is provided by a Crane adj vac unit connected to manifold vacuum [ MVA ]. Once into the throttle, the timing added by vac adv drops to zero.

    Casitron,
    You have moooocho learning to do. Don't worry, you are not alone.

    Blackout Steve took my advice with his BBC that had a radical cam & was only getting about 8" of vacuum at idle & a sh*ithouse idle. I cannot remember exactly what his idle timing was at idle after adding MVA, but it was over 50*. He was so impressed with the improvement that he rang me to thank me. He later controlled the idle timing with one of the electronic boxes, but kept the same idle timing. BO Steve used to post on Chevelles.com & USmuscle.com.au. Sadly, he passed away about 14 months ago. RIP, Steve.

    bfhoon,
    Messing around with plugs is not going to fix your problem. It needs more idle timing.


    Another quote from the Master, DV. This was in Popular Hot Rodding Magazine, Nov 2004. It was a review of Crane's all electronic dist. The smart people will notice that it has not only electronic adjustment for the mech curve, it has an electronic vac adv curve adjustment as well. Why would they go the extra expense of including VA if it was not necessary? Hmmm...

    " At idle & low speed operation, the amount of advance to most effectively utilize the air & fuel entering the engine can be as MUCH AS 50 to 55 degrees. This is handled by the vacuum advance: a function most hot rodders believe is not needed because their favourite drag racer does not use it. Now is the time to listen & listen good. A functional vacuum advance is the SINGLE MOST EFFECTIVE camshaft tamer you can get. By taking the time to hook up the vacuum advance to a MANIFOLD vacuum source you can get a big cam to idle as it were about 20 degrees less than it really is. Conversely, if you are looking for a decent idle, the use of vacuum advance will allow you to use a cam of, at the very least, 5 degrees more duration/overlap than would otherwise be the case."

    A fellow brought a big block powered car to me a few years ago. Torker intake, generic Comp Cams Xtreme energy 236/242 @ 050 hyd roller cam. Holley 780 vac sec. Turbo 400. Idled like crap at 850 in gear. With the engine idling, I loosened the dist clamp & slowly advanced the dist for the highest idle speed. Idle rpm increased 300 rpm to 1150 rpm, just by turning the dist...idle was MUCH smoother. I didn't check the idle timing but I knew from experience it would have been in the 30-40* range. The extra timing allowed the fuel/air mix to burn more efficiently. The engine made more hp, as shown by it increasing speed by 300 rpm.

  11. #26
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    Yes very good GTO. So you were using the Vac advance as a idle advance tool. So when you get on the throttle it drops the timing back to a respectable level. Fair enough. Dangerous though because using Man Vac can cause advance creep when you’re are into it.
    Yes if your lucky enough to run Electronic control ignition then the shy is the limit. High timing is for cruise conditions agreed. But that’s because you’re running lean in those conditions anyway. For fuel economy. Would never “just” use a vac advance for a retard device. Too dangerous.

  12. #27
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    Exactly, if that vac' unit ever takes a sh*t at wot, say goodbye to engine...i refuse to go that way.

  13. #28
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    Quote Originally Posted by bfhoon View Post
    So I put in one new spark plug for tuning purposes and gave the car a good 5kilometre run. The porcelain didnt foul at all but now im thinking its lean check out the new spark plug is this just a sympton of it being new? I noticed to that the idle rpm slightly increased so maybe if I replace the other 7 I will be able to adjust my idle down on the curb idle.
    Any guesses what timing im running ? IMG_0184.JPGIMG_0183.JPGIMG_0182.JPG
    Too much total, that's around 34+ looking at the annealing mark on groundstrap.

  14. #29
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    Quote Originally Posted by GtoGeoff View Post
    EH179,
    You are pretty close, you get half a cigar.... I am using locked timing, 35* & a sizeable cam. It idles better with the extra 13* of timing at idle, which is provided by a Crane adj vac unit connected to manifold vacuum [ MVA ]. Once into the throttle, the timing added by vac adv drops to zero.

    Casitron,
    You have moooocho learning to do. Don't worry, you are not alone.

    Blackout Steve took my advice with his BBC that had a radical cam & was only getting about 8" of vacuum at idle & a sh*ithouse idle. I cannot remember exactly what his idle timing was at idle after adding MVA, but it was over 50*. He was so impressed with the improvement that he rang me to thank me. He later controlled the idle timing with one of the electronic boxes, but kept the same idle timing. BO Steve used to post on Chevelles.com & USmuscle.com.au. Sadly, he passed away about 14 months ago. RIP, Steve.

    bfhoon,
    Messing around with plugs is not going to fix your problem. It needs more idle timing.


    Another quote from the Master, DV. This was in Popular Hot Rodding Magazine, Nov 2004. It was a review of Crane's all electronic dist. The smart people will notice that it has not only electronic adjustment for the mech curve, it has an electronic vac adv curve adjustment as well. Why would they go the extra expense of including VA if it was not necessary? Hmmm...

    " At idle & low speed operation, the amount of advance to most effectively utilize the air & fuel entering the engine can be as MUCH AS 50 to 55 degrees. This is handled by the vacuum advance: a function most hot rodders believe is not needed because their favourite drag racer does not use it. Now is the time to listen & listen good. A functional vacuum advance is the SINGLE MOST EFFECTIVE camshaft tamer you can get. By taking the time to hook up the vacuum advance to a MANIFOLD vacuum source you can get a big cam to idle as it were about 20 degrees less than it really is. Conversely, if you are looking for a decent idle, the use of vacuum advance will allow you to use a cam of, at the very least, 5 degrees more duration/overlap than would otherwise be the case."

    A fellow brought a big block powered car to me a few years ago. Torker intake, generic Comp Cams Xtreme energy 236/242 @ 050 hyd roller cam. Holley 780 vac sec. Turbo 400. Idled like crap at 850 in gear. With the engine idling, I loosened the dist clamp & slowly advanced the dist for the highest idle speed. Idle rpm increased 300 rpm to 1150 rpm, just by turning the dist...idle was MUCH smoother. I didn't check the idle timing but I knew from experience it would have been in the 30-40* range. The extra timing allowed the fuel/air mix to burn more efficiently. The engine made more hp, as shown by it increasing speed by 300 rpm.
    Close enough considering i know nothing about your engine. I could fine tune using my ballpark number...

  15. #30
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    Quote Originally Posted by EH179 View Post
    Too much total, that's around 34+ looking at the annealing mark on groundstrap.
    So what should i be aiming for timing wise at idle? Should I use vacuum advance or just plug it and do you think the plugs are lean?

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