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Engine hesitates during acceleration

  • November 17, 2019 9:22 AM
    Reply # 8125858 on 8121837

    That does not sound like vapor lock to me.  Vapor lock generally occurs when the engine is shut off.  With no air flowing through the engine bay, temperatures get pretty high causing fuel to vaporize in the fuel bowl.  Causing hard starting until that clears enough for fresh fuel to refill the bowl.


    What you are describing sounds more like the acceleration valve (or what Holly calls a power valve).  When you are at cruise and then floor it (or press heavily on the accelerator), a lot of air enters the engine, but vacuum drops way down & it's vacuum that draws fuel through the carb.  So, the carb has a mechanical acceleration valve that squirts more fuel in when you press the pedal to the floor.  This is especially true if after a second or two, acceleration kicks in and builds.

    Assuming that's your issue, there are two possible issues:

    1. The valve is usually made up with a rubber diaphragm.  Those get old, dry out and/or crack.  If yours is older, replace it (should be pretty easy to order a replacement accelerator valve online).  This is the most likely situation.


    2.  If it's new(ish) and done this since the Weber's been on it, it's possible you need a different valued valve.  I'm not familiar with the Weber specially, but with Holley carbs,you can get valves that squirt more or less fuel.  Yours would need one that is bigger (squirts more).


  • November 16, 2019 8:38 AM
    Message # 8121837

    When the engine is warm (30+ minutes on I-10) and I need to accelerate heavily (ie floor it) the car stutters.  My first thought was that it wasn’t getting enough air.  John Twist looked at it at the GOF and didn’t see an issue.  Any ideas?  Wondering if vapor lock or overheating of carb bowls could be a cause.  I have Webber carbs and rubber fuel lines.

    Thanks for any ideas you have.

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