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Thread: Need help with Marine 4160 4BBL

  1. #1

    Default Need help with Marine 4160 4BBL

    OK, I 'thought' it was better to replace my 30 year old QuadraJet with a new marine Holley, especially because on this engine (1988 OMC 4.3 V6) OMC and later Volvo switched from the QuadraJet to the marine 4160 part number 80492. This carb is supposedly calibrated for these V6 engines. I was able to get most of the OE parts needed for the conversion, like the carb adapter plate and the OE steel fuel line. I installed it and not matter what I did, it ran rich to the point of turning 2 sets of plugs black, had a surging idle and surged during acceleration. I tried asking techs for advice and did everything they suggested:
    Make sure that the idle transfer slot was not over-exposed. Carefully set the idle mixture (it would only idle acceptably with the mixture screws 1/2 turn out), with them the recommended 1 1/2 turns out it barely ran.
    Later on, I tried checking the floats, they were bit low and I adjusted them so they were level, same result. At this point there is no warranty on the carb (bought it new earlier this year) so in desperation, I pulled out the 30 year old QuadraJet, which I had rebuilt 2x before, with good results. I had heard they were tricky to rebuild but I did not find that to be the case at all. I just did a normal rebuild with a good cleaning and replacing all the gaskets, needle, seat, etc. Bolted it on and it ran, to my surprise, 100% better! Just like it did when I had previous rebuilds done by a shop.

    Here are the pix of the float, both were a bit low like this, and I just set them even as they are supposed to be.
    At this point I want the Holley to be usable in case I need it in the future, but I'd have to go beyond what I've done with setting it up and checking the floats. Thoughts on what else can cause this very rich running & surging?
    BTW, this carb is unusual in that there is no power valve. The primary jets (68) are richer to compensate. Also, turning in the idle mixture needles all the way will kill the engine.
    Never saw any fuel dripping from the boosters. I had some nozzle drip on my QuadraJet before I rebuilt it but the cleaning cured that.
    Last edited by Lou C; 09-15-2018 at 08:16 AM.

  2. #2

    Default

    Any ideas on this problem? I plan on taking the Holley apart over the winter and checking the metering block & metering plate for blockages, etc.

  3. #3
    Join Date
    Jan 2010
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    Brisbane, Australia
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    Default

    Check the air bleeds in the main body for blockage, a blast of carb cleaner might help.
    Your richness is lack of bleed air, or excess fuel from a idle feed restrictions incorrect size.
    Do both mixture screws react exactly the same?
    Is the secondary throttle shaft on the throttle stop at idle?
    The 68 mains and no power valve combination is NOT the cause of your idle richness.
    Last edited by Gaz64; 12-17-2018 at 12:59 AM.
    Regards, Gary

  4. #4

    Default

    Thanks. Both mix screws react the same, I had to set them 1/2 turn out just to get an acceptable idle. I'll check to see if the secondary throttle shaft is on the throttle stop at idle. I know that OMC & Volvo used this same carb on many engines, so it must be the one I got has a defect of some sort. It's just striking how much better a simple rebuild on a 30 year old QuadraJet made the engine run. Hope to get the Holley sorted as a spare.

  5. #5

    Default

    Well even though I went back to the original QuadraJet on this boat, I was still curious about what was wrong with this brand new Holley. I took the front bowl off and removed the jets, blasted out all the passages and air bleeds. Nothing seemed clogged. Then about a month later I thought of taking off the secondary bowl to see if anything was amiss there. I did this because I recall reading that supposedly fuel flows though the secondary system to an extent to keep the fuel in the rear bowl from getting stale. What I found was that the clutch bolts holding the plate over the gasket, were all loose except for one. I removed the plate and gasket, and blew out all the passages and air bleeds, again none seemed clogged. The plate was tight to the gasket though so I doubt that the loose clutch bolts were a cause of my problem. Put it all back together with a new gasket. The only other thing I noticed was that one mixture screw did not seem to thread in as far as the other. It may be that I though one was lightly seated when it really was not. Perhaps a defect in the machining of the threads on one side of the primary metering plate. Thoughts?

  6. #6
    Join Date
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    How "loose" were the metering plate screws? 1/4 turn, 1/2 turn, etc? The metering plate could have had fuel bypassing the secondary IFRS, but the discharge ports in the throttle body would then be the restriction. How much difference in seated length of the mixture screws? There could be some small differences that add up to give this scenario. Swap the screws and then compare the seated lengths. Gary
    Regards, Gary

  7. #7

    Default

    They were about a 1/2 to 3/4 turn loose, all but one. The plate was not loose though, it was stuck to the gasket pretty well. The difference in the seated length of the mixture screws was about 1/32nd". Just enough that you'd notice it.

  8. #8
    Join Date
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    And how is it running now?
    Regards, Gary

  9. #9

    Default

    I actually gave up on the Holley last summer and pulled out my 30 year old QuadraJet that was original to the boat. Previously I mistakenly assumed the Q-Jet was too old for a rebuild to work well so I went to the trouble of getting all the parts (adapter, fuel line, had to fab up a throttle cable bracket, etc.) to install the Holley (same carb that both OMC and Volvo Penta used on this 4.3L V6). And as I said it never ran right, ran very rich with surging all the time. So I took the QuadraJet, took a few hrs on a nice summer day in August and cleaned it really well and put it back together, and the boat runs 100% better, as well as it ever did. So the Holley went back in the box as a mystery and basically a waste of $400. But it is still bugging me, just what was wrong with this thing? It is a specially calibrated carb, used as OE on these engines (unlike most Holley carburetors, it does not use a power valve, but has bigger primary jets to compensate), but it would not run right no matter what I did. The QuadraJet starts in half a crank over and idles smooth, does not load up and foul plugs like the Holley did. A mystery! Not sure if those loose clutch bolts caused this but I'd sure like to know! Thanks for your feedback!

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