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  1. #1

    Default 94 4.3 Mercruiser getting 7.5 PSI from fuel pump... too much?... carb flooding after rebuild

    94 4.3 Mercruiser getting 7.5 PSI from new fuel pump... is that too much?... carb flooding... also a rebuild on old carb

  2. #2
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    Default Re: 94 4.3 Mercruiser getting 7.5 PSI from fuel pump... too much?... carb flooding after rebuild

    does sound like that pump is pushing it a bit high and that will cause the carb to flood

  3. #3
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    Default Re: 94 4.3 Mercruiser getting 7.5 PSI from fuel pump... too much?... carb flooding after rebuild

    How did you check the pump pressure? Was motor at idle speed? Make sure it doesn't rise up when its revved up a little. It is a bit high, but a carb should be able to handle that pressure. 6 to 7 psi sounds best. As a general rule, I try to keep fuel pressure below 8 psi on any type of carb. Did it start just after the carb kit? Was the carb oxidized? What led you up to this problem? Do you use ethanol fuel? Is it after being stored awhile? If the pressure rises up above that 7.5 when you rev it, then you have a fuel pressure regulator (pump integral) problem. This could have been brought on by debris, oxidation, or deterioration.
    Last edited by timguy; 04-21-2019 at 11:21 PM.

  4. #4
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    Default Re: 94 4.3 Mercruiser getting 7.5 PSI from fuel pump... too much?... carb flooding after rebuild

    float height and drop not set properly?

    Needle isn't seating?

    You may have installed the needle incorrectly on the float?
    Jack
    Mass.

  5. #5
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    Default Re: 94 4.3 Mercruiser getting 7.5 PSI from fuel pump... too much?... carb flooding after rebuild

    You could plumb in an extra fuel pressure regulator set to, say, 5 to 6 psi. Holley makes a nice one for under 30 bucks.

    Jeff

  6. #6

    Default Re: 94 4.3 Mercruiser getting 7.5 PSI from fuel pump... too much?... carb flooding after rebuild

    Quote Originally Posted by timguy View Post
    How did you check the pump pressure? Was motor at idle speed? Make sure it doesn't rise up when its revved up a little. It is a bit high, but a carb should be able to handle that pressure. 6 to 7 psi sounds best. As a general rule, I try to keep fuel pressure below 8 psi on any type of carb. Did it start just after the carb kit? Was the carb oxidized? What led you up to this problem? Do you use ethanol fuel? Is it after being stored awhile? If the pressure rises up above that 7.5 when you rev it, then you have a fuel pressure regulator (pump integral) problem. This could have been brought on by debris, oxidation, or deterioration.
    Thanks for the response.... I used a vacuum gauge and powered the fuel pump directly to check fuel pressure..... Recently got the boat, kept stalling, found that the fuel pump was not working all the time and when it did it flooded the engine. Prior to adding a new pump (because engine was stalling and age of the boat and unknown carb condition, I rebuilt the carb) Motor idles and accelerates perfectly when you pull the power to the fuel pump right before it starts running rough and flooding. A brand new carb may be able to handle the higher pressure, this carb is the original 94 and carefully rebuilt. I think FastJeff had an idea to get a pressure reg to reduce the pressure. May go that route... Yes.. uses ethanol, no carb oxidization, was stored (unknown time just recently got boat).... Thanks!

  7. #7
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    Default Re: 94 4.3 Mercruiser getting 7.5 PSI from fuel pump... too much?... carb flooding after rebuild

    I doubt that the additional .5 psi is the issue!

    Perhaps remove the needle/seat unit and check for debris between the needle and seat area.
    Look closely at the needle for any signs of damage..... and likewise at the seat area.
    Look to see if the needle/seat unit gasket is installed correctly.
    Make sure that the float is not topping out prior to pushing the needle fully into the seat.
    As Jack said..... make sure that the needle is correctly installed into the float.




    .
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP drives

    "Intellectual growth should commence at birth and cease only at death." Albert Einstein

    Please... no PMs! Post your questions on the forum.

  8. #8
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    Default Re: 94 4.3 Mercruiser getting 7.5 PSI from fuel pump... too much?... carb flooding after rebuild

    Something isn't right. As mentioned, that kind of fuel pressure is well within the ability of the needle valve to handle. If it were me, I would say that part of the price of having fun in summer 2019 and beyond is a new or remanufactured carb, new fuel lines all the way to the tank, new filters, a complete tune up with cap rotor wires plugs, and an oil change.
    Laying idle, as you know, is like the worst thing for engines. Renew as much as you can and I'm sure you will have trouble free boating. It's a safety issue, after all. You don't want to have engine trouble and find yourself adrift. Can ruin your day. Adding symptomatic cures without addressing the core issue may lead to trouble.
    Practicing the ancient art of ren-ching

  9. #9
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    Default Re: 94 4.3 Mercruiser getting 7.5 PSI from fuel pump... too much?... carb flooding after rebuild

    Did you replace the float? Non oxy fuel will provide more power and create fuel stability. Ethanol at 10 percent produces 3% less power. You may not notice a big difference in power or economy, but it is there. Make sure all your components are ethanol tolerant, if you must use ethanol. If you want to save money on fuel you can extend your ethanol by adding water.....often it happens on its own. Ethanol will suspend its own weight in water, it will burn......even having similarities to actually adding octane. Ethanol effectively adds octane, so why not add a little water too?
    Its amazing how the American consumer is getting snowed with this ethanol. Go ahead and research it, you may change your mind soon. I know its unlikely you would ever thank me, but its more likely you will say "WTF have I been doing"?
    Last edited by timguy; 04-22-2019 at 12:10 PM.

  10. #10
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    Default Re: 94 4.3 Mercruiser getting 7.5 PSI from fuel pump... too much?... carb flooding after rebuild

    You "guy" must be drinking the alcohol..........

    ALL NEW CARB KITS sold are Ethanol friendly.................ALL!

    If you actually have any experience rebuilding a Marine carb then you would know this!

    Any non metallic parts that come in contact with gas are a greenish or blueish color.............that is the design change!

    The old parts were black..........

    So all the SPEW is meaningless and has no relevance to this issue.

    Another Ricardo.............glued at the hip twins..........compardres.......two birds of a feather........
    Jack
    Mass.

  11. #11

    Default Re: 94 4.3 Mercruiser getting 7.5 PSI from fuel pump... too much?... carb flooding after rebuild

    Opted to get inline fuel press regulator (1psi-6psi) and installed it dialed at 4.5ps and I am getting better idling and restarts and no flooding out stalling. Now I need to tweak the idle jet screw...

  12. #12
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    Default Re: 94 4.3 Mercruiser getting 7.5 PSI from fuel pump... too much?... carb flooding after rebuild

    Ghost, give me your attention. I don't even drink alcohol. Ricardo is a great tech and I am in no way even worthy of comparison to him. Ethanol is garbage, it has no place in the marine industry, or in my airplane. You can have it. Ethanol produces 30 percent less power than straight petrol. The sad part is that it costs the taxpayers big bucks whether we burn it or not. Petrol fuel costs 90 cents a gallon to produce, ethanol costs $1.80......its like DAH! The ethanol producers are getting huge tax breaks and who the hell do you think is paying for that? There are 30 million acres of corn in the USA dedicated to creating this crap. We could be growing food.......like pizzas or something!
    Derfxa, now you will have to test that you have enough fuel delivery at full speed. That may not be enough pressure, depending on flow requirements.
    Last edited by timguy; 04-22-2019 at 10:04 PM.

  13. #13
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    Default Re: 94 4.3 Mercruiser getting 7.5 PSI from fuel pump... too much?... carb flooding after rebuild

    Tim, it is futile to attempt to make any sense to Mr. Ego!
    He shows all of the symptoms of megalomania!
    Just ignore him like many of us do!
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP drives

    "Intellectual growth should commence at birth and cease only at death." Albert Einstein

    Please... no PMs! Post your questions on the forum.

  14. #14
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    Default Re: 94 4.3 Mercruiser getting 7.5 PSI from fuel pump... too much?... carb flooding after rebuild

    I actually enjoy him, he adds excitement. Besides he is a dam good tech too, well.....most of the time. If we can't endure a few insults as we travel through life, then we're not gonna carry our balls in a wheelbarrow, will we? We would be nothing but *****s.

  15. #15
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    Default Re: 94 4.3 Mercruiser getting 7.5 PSI from fuel pump... too much?... carb flooding after rebuild

    ..............
    Quote Originally Posted by timguy View Post
    I actually enjoy him, he adds excitement.
    Excitement? I see it as a disruption to what would otherwise be a nice polite flow of these threads.

    Besides he is a dam good tech too, well.....most of the time.
    A little help in the departments of being polite, adult like, spelling, punctuation and the proper use of English grammar would be very helpful.


    .
    Last edited by RicardoMarine; 04-23-2019 at 07:41 AM.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP drives

    "Intellectual growth should commence at birth and cease only at death." Albert Einstein

    Please... no PMs! Post your questions on the forum.

  16. #16

    Default Re: 94 4.3 Mercruiser getting 7.5 PSI from fuel pump... too much?... carb flooding after rebuild

    Did this. Thanks! Used a 1-6psi regulator inline set at 4.5

  17. #17
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    Default Re: 94 4.3 Mercruiser getting 7.5 PSI from fuel pump... too much?... carb flooding after rebuild

    Well, I have rebuilt dozens of those carbs, think its a Rochester, and never had any trouble with them handling 7 or even 8 psi. If its a Carter, same pressures are acceptable. I still think something is wrong with your carb. If it floods out your probably gonna regret it. o2batsea will probably agree with me this time. I really think you have made a temporary solution here that might come back to bite you.
    Last edited by timguy; 04-24-2019 at 01:07 AM.

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