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  1. #1
    Cadet
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    Default mercruiser 5.0 dies

    I have 1994 5.0 liter with a mercruiser alpha one outdrive,with a quadrajet carb. The engine has a low hours but has been sittting a while. The problem with the motor is it will idle good for about a minute at 800 rpm then the engine speeds up to about 2500 and then dies.If you give the engine some gas it will keep running but it is really rough. After about 30 more secounds it will die. The engine also feels very hot to the touch after only a few minutes of running and it appears to be running rich via the large amount of black smoke coming from the exhaust. The problem to me sounded like the carb, so i bought a rebuild kit and installed it. I dont know much about carbs so i had my father talk me through it. I made sure the float was set to the charts spec. then reinstalled it. The same problem was still there. The engine also has a knocking/rattle coming from between the engine and the outdrive which speeds up with the engine rpm. I have rented a compression tester and all the cylinders were good. Any help whould be greatly appreciated.

  2. #2
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: mercruiser 5.0 dies

    The engine also feels very hot to the touch after only a few minutes of running and it appears to be running rich via the large amount of black smoke coming from the exhaust
    Sounds like you may have the choke too tight, or it is not opening. Also....If you are use to fuel injected cars and this is your first engine with a carb, you have to give it some throttle to clear it out or it will just flood itself out.Instead of letting it idle at 700 rpm, bring the throttle up to 1200 to 1500 rpm and let it warm up.Did you have water hooked to the outdrive when you were running it? If not, you have probably destroyed the raw water impeller, or it was bad to begin with. If you have an Alpha drive the impeller is in the drive, with a Bravo drive the impeller is in the engine mounted pump.Do you have a service manual?????The engine may also need a good old tuneup. Plugs, cap, rotor, set timing etc.
    Don S.


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  3. #3

    Default Re: mercruiser 5.0 dies

    And don't run it with the drive in the full up (trailering) position.

  4. #4
    Cadet
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    Default Re: mercruiser 5.0 dies

    The carb has a manual choke and it is open all the way.I alao had the water hooked up and it seemed to be spiting alot of water out of the exhuast so i guess its pumping the prop amount of water.I've tired raising the idle to around 1200 and still after a few minutes it just shuts down. When its dying I can either hit the choke or pump it a few times so it gets gas and it tries to stay running but I dont think its getting enough gas to stay running. I was thinking it might be the fuel pump or maybe a dirty filter, but I'm not sure. I also just gave it a tune up and I installed a new filter in the side of the carb. I dont have a service manual for the engine. I was thinking about buying a tempature gun to see if it is just me thinking it is get to hot.

  5. #5
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: mercruiser 5.0 dies

    Have you checked the fuel pump pressure? How about the water seperating fuel filter?
    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
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  6. #6
    Moderator Bondo's Avatar
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    Default Re: mercruiser 5.0 dies

    I was thinking it might be the fuel pump or maybe a dirty filter, but I'm not sure.
    I Think This Is your Problem...........Lack of Fuel.........You Need 4psi to 6psi of Clean Fuel, At the Carb inlet to run......It Could be Anything between the Tank,+ Carb..... including the Tank,+ Carb.....
    Any Grease is Better,..... Than No Grease at All.......

  7. #7
    Petty Officer 1st Class
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    Default Re: mercruiser 5.0 dies

    sounds like to much fuel, NOT an indicator of a plugged fuel filter, which would lean it out if anything (its never the fuel filter)if new to carbs,especially if new to them AND taken it apart, I would suggest a NEW NOT REMAN one. Carbs-=mechanical EFI=electronical, VERY DIFFERENT ANIMALS New to carbs and trying a rebuild. I would suggest getting a whole new carb no doubtyou can find them NEW 200-300 bucks online maybe chaeper if you look hard enough well maybe I should never say never, but if running overly rich it aint gonna be the filter

  8. #8
    Petty Officer 1st Class
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    Default Re: mercruiser 5.0 dies

    most likely a heavy float IF the choke working okay

  9. #9
    Senior Chief Petty Officer
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    Default Re: mercruiser 5.0 dies

    if an engine cuts out due to too little fuel (too much air not enough gas) it will do so quite abruptly when the throttle is opened with quite likely a blow back thru the carb..if it cuts out due to too much fuel (too much gas not enough air) it will do so slowly when the throttle is opened with lots of black smoke and a slow spluttery die off..the difference between the two is quite obvious.. in fact without a carb fitted at all.. simply pouring say an egg-cup full of gas into the manifold hole then cranking the engine over should produce four or five seconds of full engine rev range followed by an instant cut out when the gas u poured in runs out. basially all the clever bits in a carb aint really needed for simplistic flat out running they are more to do with economy.. clean pick up thru the engines part throttle range and steady reliable idle than anything else..idling at 800 rpm then going up to 2500 rpm and dying without touching the throttle makes no sense at all.. i think u need to make sure u have decent gas in it before going much further.. as for the engine getting hot that sounds like a completely different problem..trog100

  10. #10
    Chief Petty Officer
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    Default Re: mercruiser 5.0 dies

    My '95 5.7 was acting like this. It turned out that the ignition module was going bad. There are some troubleshooting procedures in the shop manual to go through that can identify the different problems. Just replacing parts in the hopes that you will fix the problem without knowing what is wrong can be both expensive and frustrating.

  11. #11
    Cadet
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    Default Re: mercruiser 5.0 dies

    Thank you for the replies, it turned out that the over heating problem was the water pump and the engine shutting off was the carb. I just took it to the nearst auto shop and they let it soak it carb cleaner over night, then we put it back together and its running fine. I also replaced the gas, which didnt smell old, but better to be safe then sorry.

  12. #12
    Moderator Bondo's Avatar
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    Default Re: mercruiser 5.0 dies

    The problem to me sounded like the carb, so i bought a rebuild kit and installed it.
    I'm Glad you found the problem.............There's More to a carb kit, Than Changing a few Gaskets.............. Boats.....................Quite a Learning Experince, Aren't They ????
    Any Grease is Better,..... Than No Grease at All.......

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