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Thread: poor running mid range speed

  1. #1
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    poor running mid range speed

    I have a 75 Ski Sporter with a 2011 crate 350 in it. Runs great at WOT ( 4800 rpm) and at idle. When slowing down below about 3800 rpm, the motor seems to have a miss in it. Opening the throttle, it will speed up to 4800 rpm again and seem to run fine. Motor sounds like it is missing from about 2600 - 3800 rpm. I changed from Corsa Thru hull to Straight thru hull exhaust. This was when I noticed the miss in the engine. I have changed the plugs, wires, Distributor cap, rotor and the fuel filter. Motor has less than 30 hours on it.

    Any suggestions

    Thanks
    Trevor

  2. #2
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    Could be a carb issue. Is this carbed? If so, what type?
    Member - WAFNC
    1997 22 Classic (sold)
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    Holley 4 barrel I think a 4160. I will check tonight as the boat is at the cottage. I should also be able to tell if manual or vacuum secondaries ( there is a vacuum outlet on back of carb, choke side but it is blocked off. Also, choke is not powered, never has been.

    Thanks
    Trevor

  4. #4
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    A 4160 is Holley's vac carb...600cfm but they also have a 750 under the same #. Something is weird obviously. Why did you disconnect the exhaust? Was it running fine before? If so you probably knocked off a vac line or ironically something went awry. I had a 4160 on my old Nova and was constantly having problems with it. Vowed never to own one again but it was just that particular carb that had major float problems.
    Nick
    1994 22' Classic-454 B1 Red & white
    1981 13' Whaler sport(original owner)
    South Tampa Bay, FL "May I mamoo dogface to the banana patch?"

  5. #5
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    Lightbulb

    By getting rid of the Corsa which are mufflers you may have a back pressure issue, you may need to do some jetting as you can be running lean now. Best advice on this issue will come from Buzilla. It would be a good idea to pull a few spark plugs, post a couple pf shots up here for us to take a look at.

    Phil
    No matter what your beliefs are "GOD BLESS AMERICA"

    Semi retired marine tech over 50 years in the biz.

  6. #6
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    I looked at the carb horn and the only numbers are 6057-5 and underneath 3186. The secondaries are mechanical but when I open the throttle on the carb, the secondaries do not open. The linkage does not pull far enough. the motor runs up to 4800 - 5000 with a 280 drive Solas 21 pitch Titan. The carb does have a vacuum fitting on the choke side but this was blocked from when I got the boat and there are no lines or hoses any where else on the carb. I did notice a small tube coming off the mech fuel pump but I don't see any where for this to join to It is about 2 ft long. The Corsa's don't appear to be mufflers as the sound is the same . I changed to straight tip to match original more closely. I will pull some plugs and post pictures. I also will put the Corsa's back on to see if this makes a difference. If anyone can tell me about the Holley Carb as I can't find info on it. I have a feeling this isn't a marine carb. Any info/help is greatly appreciated

    Trevor
    Last edited by tiupc; 07-18-2013 at 07:30 PM. Reason: add information

  7. #7
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    Quote Originally Posted by tiupc View Post
    I looked at the carb horn and the only numbers are 6057-5 and underneath 3186. The secondaries are mechanical but when I open the throttle on the carb, the secondaries do not open. The linkage does not pull far enough. the motor runs up to 4800 - 5000 with a 280 drive Solas 21 pitch Titan. The carb does have a vacuum fitting on the choke side but this was blocked from when I got the boat and there are no lines or hoses any where else on the carb. I did notice a small tube coming off the mech fuel pump but I don't see any where for this to join to It is about 2 ft long. The Corsa's don't appear to be mufflers as the sound is the same . I changed to straight tip to match original more closely. I will pull some plugs and post pictures. I also will put the Corsa's back on to see if this makes a difference. If anyone can tell me about the Holley Carb as I can't find info on it. I have a feeling this isn't a marine carb. Any info/help is greatly appreciated

    Trevor
    The tube goes on the blocked of fitting on the carb. That is a Fire in the bilge Bro!. That's an over flow for the fuel pump should it rupture the Diaphragm.
    machinist ,bore it deeper,ream it bigger, and lap it to a fine finish



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  8. #8
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    I don't see a 6057-5 listed here >>

    http://www.holley.com/data/TechServi...%20Listing.pdf
    Charter Member - WAFNC, SBBR, KWOSG
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    Joseph, thank you for the info re the tube from the fuel pump. It is not long enough to go to the carb. I will get a longer tube: should I connect it to the vacuum fitting on the back of the carb ?(back of the carb refers to position towards back of boat). Any insight as to why the secondaries don't open using the throttle ?
    I couldn't find this carb in a Holley listing either. Can you tell if it is a marine carb by pictures. I will also post a picture of the carb.

    Thanks
    Trevor

  10. #10
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    The tube coming from the fuel pump goes to the air breather not to any other place, if the fuel pumps diaphragm ruptures the fuel will dump into the carb. It is special and must be of the CG approved type, it also is designed to collapse in case of fire.

    A marine carb is easy to ID the bowl vent tubes are U shaped, if the carb floods the fuel dumps down into the carb.
    No matter what your beliefs are "GOD BLESS AMERICA"

    Semi retired marine tech over 50 years in the biz.

  11. #11
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    Quote Originally Posted by MOP View Post
    The tube coming from the fuel pump goes to the air breather not to any other place, if the fuel pumps diaphragm ruptures the fuel will dump into the carb. It is special and must be of the CG approved type, it also is designed to collapse in case of fire.

    A marine carb is easy to ID the bowl vent tubes are U shaped, if the carb floods the fuel dumps down into the carb.
    Both of my marine Webber and Edelbrock have a fitting at the top of the venturi .I assumed that a Holly had the same thing.
    machinist ,bore it deeper,ream it bigger, and lap it to a fine finish



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  12. #12
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    Im having the same exact problem with my Holley 650 on my X-18...same rpm range. And its definitely not electrical...changed out all that you have PLUS the ignition box (had one lying around). We're thinking we may have some piece of junk in one of the secondary jets...
    -Kev

  13. #13
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    Quote Originally Posted by joseph m. hahnl View Post
    Both of my marine Webber and Edelbrock have a fitting at the top of the venturi .I assumed that a Holly had the same thing.
    Joe we are on the same page, the point I was making is it should never be routed to the manifold or carb adapter. The engineers at tech school made a point of not having it subject to full engine vacuum, like you said many are on an air horn fitting. On my Holley it goes to a fitting on the breather similar to what is pictured below.
    Attached Images Attached Images
    No matter what your beliefs are "GOD BLESS AMERICA"

    Semi retired marine tech over 50 years in the biz.

  14. #14
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    a 4160 series is a square bore base and will have a fuel transfer tube between the bowls on the left side and is NOT normally mechanical secondary

    a 4150 series is also a square bore base and will NOT have the transfer tube, and can be either mech or vacuum secondaries

    it's best you post a pic of the carb before going further, since your not sure what model it is, and the model you say it is doesn't appear on the available literature (I have seen carb numbers in the field that are not on that literature however)

    the rpm range your having the issue may also be the peak torque hump the engine is seeing, and it needs more fuel to get over that hump, or steadily maintain it, not an unusual condition to solve

    with all that digested, IMO you have a lean cruise condition due to the primary jets being too small, or the power valve opening point being lower than needed and it's not opening soon enough. The mufflers / straight exhaust have zero to do with it. If you look at the literature. very few, if any, of the 600's have primary jets larger than 62's,,, a couple are even in the high 50's.... a 350 engine needs a minimum of a 68, if not 70-72 in the primary side, and a minimum 1 9/16 to 1 5/8 throttle blade, with a minimum 6.5 power valve in the front metering block. You have to start there. I have never been a fan of vacuum sec. carbs on a boat since the engine loading is vastly different than what a car see's in normal operation.

    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
    Charter Member - WAFNC, SBBR, KWOSG
    1955 Perfect Mate
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  15. #15
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    holley carb

    my father has a holley 4160 on his 66 16 the carb has always been tempermental try a can of seaform always had a lean condition after sitting when warm seemed as though we had this problem when we went back to go water skiing after sitting when hot anyone let me know what a good marine carb.

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