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  1. #1

    One more Carb Wizard Question

    I just rebuilt all 6 of my carbs (BN44s 1.2s and 115 gram springs). I was doing my pop off tests and 4 of the 6 carbs had a leak at the pump body base gasket at about 30 or 40PSI. These are genuine Mikuni kits (from Group K). I am a good student and saved all my gaskets and had them laid out in order for each carb. They all match perfect and the order is correct (even watched videos on internet and they look same as mine). Rubber rings thickness look the same etc. Soapy water confirmed every time it was where the base diaphragm/gasket meets the body of the carb (yes I made sure it was not the BN38 diaphragm in there and matched the ones I took out)). I finally got tired of pulling it apart and putting it back together only to have a slight leak. I put the thinest coat of 1211 around the gasket and diaphragm assuming it was where they both met each other. Sure enough problem solved and and the popoffs were all around 75 (where they should be). I just want to know what the heck is going on. I read some others have problems where the oring was smaller but that is not where mine is leaking (all base). Anyone else seen this? I am kind of a perfectionist and am losing sleep now, so want to understand why I had to use 1211 in that one spot. Any insight or just knowing I am fine and others have seen this would help me sleep at night.


  2. #2
    butterbean_29512's Avatar
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    Are you tightening the screws tight enough? The bodies need to be clean...and the screws holding the carb together need to be tight.

  3. #3
    Soda blasted and then ultrasonic cleaner. So about as clean as you can get. They are cranked down. I drew an arrow in picture below which is where the 4 all leaked. The parts underlined were all in each carb pulled apart. There was clear indents where the 6A rubber ring should go and part 5 and part 6 were in each carb. I have even watched some videos of BN44 rebuild and all those parts in theirs also. Gasket 6 and diaphragm 5 is what I put lite coat of 1211 on. Just wondering if I should be worried or if it is acceptable to have 1211 on it.
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  4. #4
    They are just castings...... did you try a straight edge to see if they're actually flat? Or is there a weaker spot(less supported) on the body at that corner that distorts under load. OR... leave the 1211 alone and go to sleep.

  5. #5
    I did not try a straight edge but I have a hunch now. My buddy has same year boat so we pulled 1 pump apart. Gasket 6 was not in any of his. I suspect with the rubber 6a on the diaphragm damper (5) if you add the gasket (6) it is to thick and leaks there. I talked to Harry at Group K and he said there can be several variations on that pump in the BN44. I think whoever rebuilt them last time got gasket happy and did not really compare the old ones coming out but instead used that drawing above. My service manual also shows no gasket 6 also (but has been wrong before). That being said the leak spot was the same on every single one where I have the red arrow. I pulled the extra gasket from each carb but still had to put a little 1211 there to get them to not leak (with soap test) on all 6 carbs (maybe from taking them apart 20 times). Anyhow after I sealed the pumps with very light 1211 I put them on the banks and put about 40 lbs into the whole bank. It held there with zero drop and when I sprayed soap on the pump bodies they were sealed. I just hate that I had to 1211 something that shouldn't be.

  6. #6
    I don't have a solution, but just some observations from personal experience (I also have six SB44s ). None of mine use both gaskets 6 and 6a. Pretty sure it should be one or the other, and I'm running 6a's with no problems.

    That said, the first time I rebuilt my carbs I used non-Mikuni kits (bad idea). I got the same leak you describe from two or three of my carbs. I replaced the new aftermarket 6a gaskets with the old Mikuni's, and problem solved. I have since replaced the aftermarket kits with Mikuni's for other reasons and have not had the leaks return. You mentioned that you used Mikuni kits, so this probably isn't your issue, but I thought I'd mention it anyway.

    I have read posts from people stating that checking pop off is over rated. You should just use the correct Mikuni needle/seats and springs and forget about it. I always check pop off if for no other reason than to detect a leak that you might not otherwise know about until your on the lake.

  7. #7
    I also had a leakage problem near the hull. On carburetors gp1200r. I added an additional black gasket from the old kit, then there were no leaks.

  8. #8
    Thanks guys... I feel better knowing others had the issue as well. For now my 1211 fix seems fine. Next time I break them down I will see if I can get them to seal with no 1211 and right gaskets the first time. I have a feeling that had I not stuck the other gasket against the damper in first place it might of sealed fine. Maybe just peeling it back apart caused an issue.

  9. #9
    steve45's Avatar
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    I've found castings that were not properly finished on carbs. I think you're OK.

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