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Thread: poor running mid range speed

  1. #16
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    Quote Originally Posted by BUIZILLA View Post
    max tuning a 4160 series with rear metering blocks is an expensive and time consuming PITA

    just my .03, and i'm SURE somebody will disagree
    Having gone through that whole process, I AGREE!
    “Oh right, because you walked into strippers discount warehouse and said ‘Help me showcase my intellect.’” - Archer

    Bill
    Grand Rapids, Michigan
    1985 Donzi Criterion SS
    1967 Donzi 16 Ski Sporter, C16-409, Has a new home!
    38' Carver Aft Cabin
    1968 Sea Ray SRV 180 w/1975 70 hp Evinrude
    10" RIB w/15 hp 1984 Evinrude

  2. #17
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    photo 2.JPGphoto 4.JPGphoto 8.JPGphoto 9.JPGphoto 10.JPGphoto 6.JPGphoto 5.JPG

    Plug on left is #6 and right is #4 4th pic shows number of 8050B

    Since this is an automotive carb, would I be better to purchase a marine carb probably a 0-80551 Holley or Mallory Any other suggestions ? Thanks to all who have taken the time to answer.

    Trevor
    Canada

  3. #18
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    here's my take on the pic's >

    get rid of that spacer

    by looking at the plug strap color the timing is pretty close, might stand to be advanced another 2*...

    good upper ceramic color ring on the lower plug, lean on the upper plug, gaps look different, I can't see the lower internal ceramic color, but what I do see is very typical of a badly jetted dual plane intake, with maybe partially plugged main housing air bleeds

    the 80457-5 isn't on my chart... but I would throw in a pair of 69 front jets and a new 6.5 PV in the front side, kill the spacer, and get a 1/4" bakelite spacer instead, advance the timing 2*, no more than 32* total and see what happens for giggles

    if the timing is already there, then you have crappy slow burn fuel because I see some residue on the strap that shouldn't be there
    Charter Member - WAFNC, SBBR, KWOSG
    1955 Perfect Mate
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  4. #19
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    Thank you Jim for looking at the pictures. My concern now is that this is an Automotive carb. There is no place to connect the overflow tube from the fuel pump. I believe this is a fire hazard. Would a Holley 0-80551 (4160 or Mallory equivalent work.

    Thanks

    Trevor

  5. #20
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    Trevor

    Well the carb is a vacuum secondary carb not mechanical. You can see the vacuum actuator in the picture of the carb from the opposite side of the throttle linkage (picture #6). The secondaries will never open when you open the throttle all the way without the engine running, it only opens with vacuum.
    There is a small vacuum port coming out of the metering block (picture #6 also) that is open, that needs to be plugged or connected to the distributor, but being this is a boat engine and there is usually no vacuum advance in the distributor, you should plug it.
    On the secondary actuator it says Performance Carb. these carbs are usually jetted richer then standard automotive 4150/4160 carbs.
    One more point, make sure the choke plate is under spring tension to stay open all the time if you are not using it, by rotating the black choke housing.

    Just adding to what has already been stated.

    Good luck
    Steve
    ps Presently also in Canada (Montreal area working)

  6. #21
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    Member - WAFNC
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  7. #22
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    Quote Originally Posted by tiupc View Post
    Thank you Jim for looking at the pictures. My concern now is that this is an Automotive carb. There is no place to connect the overflow tube from the fuel pump. I believe this is a fire hazard. Would a Holley 0-80551 (4160 or Mallory equivalent work.

    Thanks

    Trevor
    1409.jpg
    machinist ,bore it deeper,ream it bigger, and lap it to a fine finish



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  8. #23
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    Quote Originally Posted by BUIZILLA View Post
    here's my take on the pic's >

    get rid of that spacer

    by looking at the plug strap color the timing is pretty close, might stand to be advanced another 2*...

    good upper ceramic color ring on the lower plug, lean on the upper plug, gaps look different, I can't see the lower internal ceramic color, but what I do see is very typical of a badly jetted dual plane intake, with maybe partially plugged main housing air bleeds

    the 80457-5 isn't on my chart... but I would throw in a pair of 69 front jets and a new 6.5 PV in the front side, kill the spacer, and get a 1/4" bakelite spacer instead, advance the timing 2*, no more than 32* total and see what happens for giggles

    if the timing is already there, then you have crappy slow burn fuel because I see some residue on the strap that shouldn't be there
    I tried my 400, with and with out a thermal spacer. I used a single plane 1" spacer .I lost 250RPM right off the top by taking it off. It did have slightly better throttle response at lower RPM with out it. But 250 RPM loss is huge. I think your onto something with the power valve. A vacuum gauge is always handy when setting up a Holley
    machinist ,bore it deeper,ream it bigger, and lap it to a fine finish



    https://www.facebook.com/photo.php?v...=2&theater

  9. #24
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    Quote Originally Posted by joseph m. hahnl View Post
    I tried my 400, with and with out a thermal spacer. I used a single plane 1" spacer .I lost 250RPM right off the top by taking it off. It did have slightly better throttle response at lower RPM with out it. But 250 RPM loss is huge. I think your onto something with the power valve. A vacuum gauge is always handy when setting up a Holley
    problem is, he has a dual plane intake... and a thermal spacer doesn't have the ribbed internals, and isn't metal either... a spacer is used to tune runner length characteristics and can be VERY beneficial up top, mid range not so much.. as was pointed out before, that open vacuum nipple and too small jets could be the only issue.. good catch on the open vacuum nipple, as that is a ported nipple and really only see's a vacuum reference once the throttle is opened..
    Charter Member - WAFNC, SBBR, KWOSG
    1955 Perfect Mate
    1986 Hornet III, 502-415 TRS

    www.donzi.org


  10. #25
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    Lightbulb

    Since he has an automotive carb his best move would be to find a marine 650, 750 on a 350 is a bit much. I run a 750 on my 383, I think it would run nicer with a 650. A 650 may take a tiny bit off my top end but who cares!!!!
    No matter what your beliefs are "GOD BLESS AMERICA"

    Fully retired marine tech near 60 years in the biz.

  11. #26
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    Yup, Edelbrock 600

    Quote Originally Posted by joseph m. hahnl View Post
    For under $300 you can buy a 600CFM Edelbrock with an electric choke bolt it on and go boating...
    Thank you, Patrick
    1994 18' Classic 350Mag Alpha

    Previously owned Donzis -
    1996 22' Classic, 502Mag Bravo
    1987 20' Minx, 350Mag Alpha
    1975 18' Classic, 350Chevy Volvo 280

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