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  1. #1
    Join Date
    Aug 2018
    Location
    Nelsons county Norfolk england
    Posts
    16

    Default Carb help merc 70 1989

    I have a problem. After changing a couple of bits I decided to strip the carbs as I knew a couple of carbs had the float stuck. On putting it all back together it wonít fire. When priming the bulb it goes hard and wonít let anymore fuel in feels solid. Iím sure I should be able to squeeze fuel into the engine. Not sure if Iím right but anyhow i does try to fire when I squirt some down the he carbs. Any idea?? 😁 maybe did something wrong? Itís an engine that came with my boat and had no spark but now has and ready to go if I can get some fuel in 😁

  2. #2
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    15,692

    Default Re: Carb help merc 70 1989

    Those carbs have a weird problem when they get old--the floats contact the bottom body of the carb and jamb. Not sure why they do it, but...

    Here's what to do: First of all, verify that the float is tuck by unscrewing the main jet holder and pumping the bulb; gas should dribble right out.

    The 'test': With the carb off (and empty), put it carb next to your ear and shake it. If all is well you will hear the float ratting about inside.

    The cure: Remove the float and carefully sandpaper away the casting flash (plastic that squeezed out of the mold during casting). Repeat the test above

    Good luck!

    Jeff

    PS: Usually the float sticks in the down position, which causes massive flooding.

  3. #3
    Join Date
    Aug 2018
    Location
    Nelsons county Norfolk england
    Posts
    16

    Default Re: Carb help merc 70 1989

    Thanks Jeff I will definitely try that. When I take the carbs off they seem full after I took them off. All three had a lot of fuel in. but the plugs aren’t wet after turning it over. I. One thing I did notice is the rubber seal looks pretty squashed that the main jet tube sits against to form the seal kind of like the straw bit where it’s sucked uk from the main jet. Il take them off and give your suggestion a try tomorrow. Thank you for a response ��

  4. #4
    Join Date
    Dec 2015
    Location
    maplevalley WA
    Posts
    5,049

    Default Re: Carb help merc 70 1989

    To check for fire just put some fuel mix directly in the plug holes and quicklyput the plugs in and see it you get fire? Make sure your in a barrel of water in case it starts to run. I just use a length of fuel line dip it in the tank and plug the end with your finger stick it in the plug hole and release your finger. If it dont fire first check compression then check for spark with a spark gap tester. The spark must jump a open air gap of at least 3/8 inch with a crisp blue snap?

  5. #5
    Join Date
    Aug 2018
    Location
    Nelsons county Norfolk england
    Posts
    16

    Default Re: Carb help merc 70 1989

    Hiya yes I have a good spark on all three cylinders. Yes when you put fuel mix in directly it does try to fire. Initially had a spark problem which was the switch box but the engine would still try to fire on the one cylinder that sparked. Now all spark nicely but no fuel is getting beyond a certain point in the carbs and will only try firing with a squirt directly into the carbs. I decided to clean the carbs and it won’t fire since putting them back on. I’m going to check the floats again but will need to check fuel pump next I’m guessing?
    Only thing didn’t know how to clean was the emulsion tube? That picks up from the main jet as I don’t know how to remove that bit for cleaning.
    ��

  6. #6
    Join Date
    May 2015
    Location
    Crosslake, Mn
    Posts
    68

    Default Re: Carb help merc 70 1989

    Your carbs are not clean. If you have fuel in your float bowls, high quality spark, good compression in the cylinders, NO MATTER what you think, THE CARBS ARE NOT CLEAN.

    Carburetors may look like very simple devices but they are very complex engineering. The fluid dynamics that makes them work depends on small specifically located passages. When you cleaned the carbs did you probe all the very small holes in the venturi with a soft piece of copper or brass wire. I assuming you soaked them in carb cleaner (maybe even over night). Scrub all the surfaces with a soft brush (like a toothbrush). Probe the small holes. Blow ALL the passages with compressed air (both forward and backwards). Did you rinse them thoroughly first with extremely hot soapy water. Probe the small holes (again). Blow ALL the passages with compressed air (both forward and backwards again). Did you rinse them thoroughly a second time with extremely hot water (No soap this time). Blow ALL the passages with compressed air (both forward and backwards a third time). At this time ALL the part should look like they just came out of the original manufacturing process. Time to carefully reassemble all the pieces with fresh gaskets.

    Your local marina wants hundreds of dollars to do this work. They may have some shortcuts (like ultrasonic cleaners). But there is a lot of putsy labor invoked. That is why it cost so much.

    I am sorry I vented on you. But when I hear that "it was sorta working and I cleaned the carbs and it is not working now...." You did something WRONG. Carb cleaning is an art and a science. Just remember that that block of metal is a very complex device, and take your time. It should look like you just bought a new one when you are done.

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