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Technical Rochester BC carb leaks fuel. What's going on here?

Discussion in 'Traditional Hot Rods' started by Six-Shooter, Dec 3, 2013.

  1. Six-Shooter
    Joined: Jul 12, 2010
    Posts: 341

    from Ohio

    I have a '57 Rochester BC carb on the Chevy 235 in my T-bucket. Lately, after sitting a couple of days I find fuel has leaked from the carb (I believe from around the accelerator pump - see photos). I'll clean it up, run the engine, and don't notice any leaking fuel while under power. However, let it sit again for a couple of days and the fuel leak returns. Any thoughts as to what is going on. Also, should I rebuild the carb (I've never done one before) or replace the Rochester BC with something else. If so, what do you recommend? Thanks!!!

    Attached Files:

  2. choppedtudor
    Joined: Nov 28, 2009
    Posts: 683


    could be the float is set too high, no outside adjuster screw on those carbs, need to bend the float arm to adjust per specs in rebuild kit. Also recheck your fuel pressure.
  3. gas pumper
    Joined: Aug 13, 2007
    Posts: 2,956

    gas pumper

    And for ethanol fuel, it's density is lower than old gasoline, so I found that 3/16 lower float height helps get the fuel level better. Helps the leaking, but won't stop it. It's traditional Rochester patina!
  4. theburningbush
    Joined: Jan 2, 2011
    Posts: 20

    from Tacoma WA

    I've rebuilt many Rochester BC's... Most of the time the cause of leaks is the gasket between the fuel bowl and air horn (the two main aluminum pieces)... sometimes the top piece gets warped from overtightening the screws or from gasket deterioration. You may have noticed the leak getting worse if you re tightened them to stop the leak. Replace gasket, if it still leaks put In two... The second most likely option is a faulty needle and seat. There is a tang on the opposite side of the float that operates the needle (fancy plug) ... Float is on a fulcrum so fuel level drops it let's gas in, it rises and stops the flow by pushing the needle into the seat... if this fails it usually leaks gas out the vent holes at the top... And usually when running. Or leaks all your gas back into the tank and u have to crank forever. Third possibility is worn throttle shaft (butterfly at base of carb) as it wears you get fuel leakage (and air) that may exit along the shaft, to fix this u have to install bushings (easier to swap the part from another carb unless you have the right reamer and bushings)... All that being said I would do a rebuild first. napa has a good quality kit, or AutoZone Carries a kit from a company called hygrade kit number 123a ... it's probably the easiet carb to rebuild, just don't over think it! You know it runs, and didn't always have a leaking problem, so check it float level as per instructions but u probably won't have to adjust it! Don't take out your butterfly shafts u know they work fine! And the little brass screws break every time... Just spray it out with carb cleaner after disassembly and put it back together... Take digital pics of every step and about six pics from different angles before u start... Run into any problems send me a message! Parts kit is about $20,

  5. inline 292
    Joined: Aug 25, 2006
    Posts: 296

    inline 292

    You stop your motor & have trapped fuel pressure between the F. pump & the carb inlet valve. Engine heat rises up, warms that fuel line, & creates even more pressure. The pump check valve seals that end. Your carb inlet (float) valve leaks a bit, it overflows the float chamber, & drips down onto the throttle plate. Runs across it, & out the shaft to carb base bore clearance. Replace the float valve, & lower the float level to give room for some expansion.
  6. StefanS
    Joined: Oct 7, 2013
    Posts: 1,098

    from Maryland

    Sorry to re-start an old thread (and sort of change the subject)but...I just rebuilt my bc and now it starts beautifully the first time of the day and runs great the entire time I'm driving, but if I turn it off after it's been running for a bit I need to pop start it or it just cranks and cranks (and cranks). Once I pop it it runs perfectly again. Any ideas on what could be causing this?

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