Hooooooray I found the air leak!

Discussion in 'Motorized Bicycle General Discussion' started by Nougat, Mar 14, 2011.

  1. Nougat

    Nougat New Member

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    Second build is now roadworthy, after I lucked into solving an air leak. The RPMs would race away, so I did the carb cleaner test and came up with nothing. I was worried I'd have to replace crank seals, but remembered that I still had another carb o-ring from SBP. I vaguely remembered that it would fit in the carb top, so I gave it a try.

    Perfect throttle now, probably better than my other bike. I am so ready for the weather to break.
     
  2. dmb

    dmb Active Member

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    o-ring on top of the slide? tell me more.
     
  3. Nougat

    Nougat New Member

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    Yeah, unscrew the carb top and stick the o-ring up in there. You'll need a little screwdriver or something to seat it. Screw the top back on a little snug and you're done.

    The rings from SBP come in a three pack. One for the carb to intake, one for the carb top, and one for a spare. Well worth it, better than sealer goop for sure. And they're made from Viton, so they're fuel compatible.
     
  4. ruppster

    ruppster Member

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    Nougat, Check your other carb to make sure your slide is opening all the way.
     
  5. Nougat

    Nougat New Member

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    Oh it is. I get 32 or 33 MPH from that one, a 26" cruiser, and I'm about 215 lbs. I'm just thinking back to last season, it might have a teeny weeny air leak, because it doesn't return immediately to idle when I close the throttle.
     
  6. fall_down_stand_up

    fall_down_stand_up New Member

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    You can also buy O rings at your local hardware store or auto parts store if you cant wait to get them online....I know for me,when I am ready to ride I want to ride right now lol....
    John
     
  7. Nougat

    Nougat New Member

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    Yeah, turns out my left crank seal was totally trashed. I still like the o-ring, though.
     
  8. 2door

    2door Moderator
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    All carburetor installations are subject to air leaks in the slots cast into the carb throat where it tightens against the intake manifild. Using an 'O' ring in the carb doesn't assure that you're getting a good, airtight seal there. Those slots can extend past the 'O' ring seating area allowing an air leak. This is why we recommend a sealant such as a product called SealAll to assure a good seal. Silicone based sealers, for the most part, are not gasoline resistant and over time will be attacked by the gasoline, soften and allow air to pass. Read the package of any sealer/gasket maker product and most will say, 'Not compatible with gasoline" . They will work but only temporarily.
    A majority of lean/fast idle conditions can be traced to air leaks in the intake manifold/carburetor/cylinder area. Crankshaft seals are also notorious for causing this condition but the intake system is more commonly the culprit.
    Other causes have been found such as defective carburetors, cracks in the welds on the intake manifold and defective intake to cylinder gaskets.
    Tom
     
  9. Nougat

    Nougat New Member

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    Yeah, I tried some Permatex that claimed to be gasoline compatible, and it ended up being a goopy mess. I don't doubt that there is a stuff that would work better, but I decided to roll the dice on some o-rings (since I was buying a bunch of other parts anyway), and it worked for me.

    It's been a while since I put the one in the neck by the intake on the newer bike, and much longer for the older bike, but I don't recall any issue with overlap with those slots.

    When I eventually have to take one of these carbs off for some reason, I'll make sure to inspect those o-rings for deterioration, and follow up.
     
  10. 2door

    2door Moderator
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    The trick with using the 'O' ring in the carb throat is to apply a lot of pressure against it when tightening the clamp that holds the carb to the intake. Simply sliding the carburetor up against the 'O' ring doesn't assure a snug, airtight seal.
    I've had very good results with Seal All although I will admit it requires some work if you ever need to disassemble things. It holds tight.
    Tom
     
  11. Acraze

    Acraze Member

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    Anyone have pictures on this. Pics could help a ton. Mine has been idling high, so I did a carb cleaner test and found it to be a problem at the carb throat. I put a oring in there but now I have no throttle twist. Should the oring be on the outside of the carb slide or small that it tucks inside the slide?
     

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