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Results 1 to 26 of 26
  1. #1
    Join Date
    Jul 2009
    Location
    Orangevale, CA, USA
    Posts
    12

    Angry Mercury Carburetors Leaking

    Two of the 3 carburetors are leaking gas on my 40ELPT, 4S, outboard (2000 year) motor. The leaks are between the float bowl and body, next to the plunger. I have rebuilt these twice, and used a new gasket kit the last time. The motor has very few hours, and looks brand new, but, I can't synchronize until I stop the leaks. I checked the float level, appears OK. Does anyone have any ideas, or do I assume the carbs are warped, or somehow shot??
    Thanks for any help.
    Riocasa

  2. #2
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    17,311

    Default Re: Mercury Carburetors Leaking

    Had that same problem lately.

    It's hard to do, but you need to determine it the float bowl gasket is leaking, or if it's flooding.

    Remove the carbs (again!) and rig up the gas hose right to them, one at a time. Pump the bulb until the leak happens and study where it's coming from. If it's that damn gasket--and I had a new one leak badly on me--you might want to reuse the old one. (Fastjeff's Law: "Never throw anything away!") If you round-filed the old one, then you'll have to improvise.

    If you're sure it's flooding, try lowering the float level a 1/16 of an inch at a time until it stops. Contrary to popular opinion, the float level can be set WAY lower without effecting performance. I used to run the Holley carb on my autocross car a full 1/8 " lower than "correct" to clean up its performance on bumpy tracks. The 1/8 " lowering had NO effect on output whatsoever.

    Jeff (with 50 years of carb experience)
    Last edited by fastjeff; 04-21-2010 at 06:29 AM.

  3. #3
    Join Date
    Jul 2009
    Location
    Orangevale, CA, USA
    Posts
    12

    Default Re: Mercury Carburetors Leaking

    Jeff, thanks much! I'm now sure the leaks are coming from in front of the gasket from a hole with a brass plug with a small gap on either side (vent?); points to a stuck float (even with a new needle). When I first sprayed carb cleaner in the plunger hole, it flowed out between these gaps, but, after more cleaning, no more leakage around the plug. What do you think of using WD40 around the float pin (the float appears in good shape)? Riocasa

  4. #4
    Join Date
    Jul 2009
    Location
    Orangevale, CA, USA
    Posts
    12

    Default Re: Mercury Carburetors Leaking

    I just discovered that the top carb, float to housing gasket has an "O-ring" attached to it, that surrounds the brass plug (where the leaks are occurring). Neither of the other two has this O-ring attached, and they are leaking (including the new kit I just bought). I cannot figure out why these carbs have not been leaking before, since I used the boat last year. Nobody at Mercury Marine or the Parts stores can help me understand which is normal, and I am confused re the brass plug, and what might happen if I seal it with an O-ring (if I can find one that size!).
    Riocasa

  5. #5
    Join Date
    Jul 2009
    Location
    Orangevale, CA, USA
    Posts
    12

    Default Re: Mercury Carburetors Leaking

    To complete this thread, I located the proper gasket through Boats.net. It is important to talk to them since for every motor there are dozens of Models, and you must select the right one for the kit. Unfortunately, I got the wrong kit which did not have the small O-ring attached to the plunger plug, hence, the leaks. I solved for now by inserting a small, unattached O-ring, and the leaks stopped. The kits cost $40+ (must buy entire repair kit for one gasket), so an expensive mistake. I will now get a professional carb sync, and in the future, will not leave "old gas" in the carbs after use!
    Riocasa

  6. #6
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    17,311

    Default Re: Mercury Carburetors Leaking

    We all learn! If you think that carb kit is expensive, the Merc 25 kit costs over 80 bucks!

    Jeff

  7. #7
    Join Date
    Jan 2009
    Location
    marion , ar., usa
    Posts
    61

    Default Re: Mercury Carburetors Leaking

    your still getting off cheap try taking in to a shop $$$$$

  8. #8

    Default Re: Mercury Carburetors Leaking

    Check your float it might have fuel leaking into it which will weigh the float down giving it to much pressure inside the carburetor fuel bowl

  9. #9
    Join Date
    Dec 2019
    Location
    Las Vegas, NV
    Posts
    45

    Default Re: Mercury Carburetors Leaking

    Quote Originally Posted by fastjeff View Post
    Had that same problem lately.

    It's hard to do, but you need to determine it the float bowl gasket is leaking, or if it's flooding.

    Remove the carbs (again!) and rig up the gas hose right to them, one at a time. Pump the bulb until the leak happens and study where it's coming from. If it's that damn gasket--and I had a new one leak badly on me--you might want to reuse the old one. (Fastjeff's Law: "Never throw anything away!") If you round-filed the old one, then you'll have to improvise.

    If you're sure it's flooding, try lowering the float level a 1/16 of an inch at a time until it stops. Contrary to popular opinion, the float level can be set WAY lower without effecting performance. I used to run the Holley carb on my autocross car a full 1/8 " lower than "correct" to clean up its performance on bumpy tracks. The 1/8 " lowering had NO effect on output whatsoever.

    Jeff (with 50 years of carb experience)
    Hello, found this old thread...I'm having the same problem! Not used to working on tiny carbs like this but can't get these 77 Merc 500 carbs to stop leaking. Never had this problem before. When you mention lower float height, you mean lower it when it's upside down or right side up?It's not a major leak but I'm stumped, have replaced floats, gaskets twice, still leaking from bottom plug or bowl. Thought I finally had it, pumped up firm last time, I waited a min pumped hard, and leak began again...

  10. #10

    Default Re: Mercury Carburetors Leaking

    Can you post a pic (200 kb) of the carb, there are 2 types.

  11. #11
    Join Date
    Dec 2019
    Location
    Las Vegas, NV
    Posts
    45

    Default Re: Mercury Carburetors Leaking

    Quote Originally Posted by Quicksilver View Post
    Can you post a pic (200 kb) of the carb, there are 2 types.
    Here is pic, hope it attaches
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Screenshot_20191222-125934.jpg 
Views:	9173 
Size:	499.6 KB 
ID:	22412  

  12. #12

    Default Re: Mercury Carburetors Leaking

    What is that white gunk, silicone? I think your problem is you're missing gaskets in '33"Click image for larger version. 

Name:	77carb1.jpg 
Views:	6645 
Size:	196.1 KB 
ID:	22413
    If you want to set the float level follow the second page instructions.Click image for larger version. 

Name:	77carb2.jpg 
Views:	613 
Size:	158.2 KB 
ID:	22414

  13. #13
    Join Date
    Sep 2010
    Posts
    24,192

    Default Re: Mercury Carburetors Leaking

    It looks to me that the white stuff is a repair of the linkage between carburetors.

  14. #14
    Join Date
    Dec 2019
    Location
    Las Vegas, NV
    Posts
    45

    Default Re: Mercury Carburetors Leaking

    I'm going to order kits and try it again with new gaskets... I have triple checked float levels per the manual, but am thinking of also trying a lower setting, as recommended by fellow that posted before.

    Also, don't mind that throttle coupler Lol. I snapped it removing the carbs so plastic welded it together and put adhesive on it. Want to make sure this thing works right before replacing anything

  15. #15
    Join Date
    Dec 2019
    Location
    Las Vegas, NV
    Posts
    45

    Default Re: Mercury Carburetors Leaking

    Just ordered kits to try again, but I think I may have finally found my problem. Watched a YouTube video where they rebuild my exact carbs, I think I have the main gasket that attaches the carbs to block (flange gaskets) backwards and/or flipped, so the vent hole is not lining up with carb and making an overflow situation. I hope I found the problem!

  16. #16
    Join Date
    Sep 2010
    Posts
    24,192

    Default Re: Mercury Carburetors Leaking

    No ---That is the hole used to drive the fuel pump.----Not a vent and not your problem !

  17. #17
    Join Date
    Jun 2013
    Location
    Duluth Mn
    Posts
    4,868

    Default Re: Mercury Carburetors Leaking

    Does it leak when it's at rest? How hard are you pumping the primer bulb? Any carb will leak past the float valve if there is excessive pressure.

  18. #18
    Join Date
    Dec 2019
    Location
    Las Vegas, NV
    Posts
    45

    Default Re: Mercury Carburetors Leaking

    Does not leak at rest, or when it's running from what I can see. I pump it up until it's firm and just then when bulb is firm, after I hear bowls fill up, usually begins to leak, mostly from the bottom plug. Another time it leaked from side of bowl, and one time fuel even shot out of front of carb. It's been a journey to fix these.

  19. #19
    Join Date
    Dec 2019
    Location
    Las Vegas, NV
    Posts
    45

    Default Re: Mercury Carburetors Leaking

    I am stumped. Float levels look perfect, needles and floats are new, no gunk in the seats. Going to rebuild again with new kits with the manual at my side and triple check everything.

  20. #20
    Join Date
    Jun 2013
    Location
    Duluth Mn
    Posts
    4,868

    Default Re: Mercury Carburetors Leaking

    Your primer bulb is providing too much pressure perhaps. When did the problem first start? Either that or your floats are soaking in fuel......too heavy......"fuel logging". You said you put new ones in?

  21. #21
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    5,481

    Default Re: Mercury Carburetors Leaking

    You have to use OEM needles as I have see to many of the aftermarkets the spring on needle is weak
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  22. #22
    Join Date
    Dec 2019
    Location
    Las Vegas, NV
    Posts
    45

    Default Re: Mercury Carburetors Leaking

    Motor was sitting for years so after compression check, started with carb rebuild. I think I will try a new fuel line and primer bulb. I'm using a 3/8" fuel line. One odd thing is I do hear a lot of "air sucking" when I prime the bulb, which is odd. I did rebuild fuel pump/carb with Oem Merc kits.

  23. #23
    Join Date
    Jun 2013
    Location
    Duluth Mn
    Posts
    4,868

    Default Re: Mercury Carburetors Leaking

    You must be building too much pressure or introducing small particles of debris. That would create a seating problem for the needles. I have seen this before. It often occurs on sunny days with poor tank venting.
    Last edited by timguy; 12-24-2019 at 03:26 PM. Reason: Typo

  24. #24
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    5,481

    Default Re: Mercury Carburetors Leaking

    Travis......3/8 line is too big..use the 5/16 line, loose the hose clamps and use fuel ties. This wont solve the flooding but will prevent fuel/air leaks
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  25. Default Re: Mercury Carburetors Leaking

    I have the exact same engine. Did you solve your leakage?
    Is your engine hard to start? Mine takes maybe 15 spins.
    Quote Originally Posted by travis0332 View Post
    Here is pic, hope it attaches

  26. #26
    Join Date
    Dec 2019
    Location
    Las Vegas, NV
    Posts
    45

    Default Re: Mercury Carburetors Leaking

    Quote Originally Posted by Bob in Tennessee View Post
    I have the exact same engine. Did you solve your leakage?
    Is your engine hard to start? Mine takes maybe 15 spins.
    Yes. The manual's recommended float height of 1/4" was too low for mine...I set them higher, probably around 5/16" to stop the flooding. Leakiest carbs ever. With that being said, you still need to be careful priming these little devils...the only thing stopping a waterfall is the doinky little weak spring attached to the inlet needle.

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