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Thread: Weber Carbs

  1. #1

    Weber Carbs

    Hello all, a tuning question on my weber cars. I have a '69T with MSD ignition. Valves were just adjusted and spark plugs are new. I was having some idle issues so I did some adjusting on the idle mixture screws...car idles at just a hair over 1,000 when cold and warmed up and pulls strongly throughout the RPM spectrum, but I am having some popping on deceleration in the 2,000RPM area. Any thoughts on how to rectify this? Would it be directly related to air correction screws? Synchrometer levels are measuring pretty even across each throat.

    Any help is much appreciated!

    Thanks
    Tim

  2. #2
    Senior Member
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    Idle is too high. Do you know why? Should be around 850 to 900 rpms. I'm far from an expert, but I have played a lot with the Webers on my car including rebuilding them myself. Assuming you don't have any exhaust leaks (which can cause this), it sounds like you have an intake leak that is sucking air. Check the carbs to manifolds gasket area as well as the manifold to head gasket areas. You can spray those area with Carb cleaner or WD40 and see if you get an idle change which would help you locate the air leak. That's my uneducated guess as to where I would start.
    Last edited by gsjohnson; 04-26-2014 at 11:14 AM.

  3. #3
    As gs johnson just mentioned, but I want to emphasize, look for pin hole leaks (always a dark spot) in the heat exchangers and muffler. Also look for carbon stains around gasket areas. This is often the culprit on decel backfiring.
    Early S Registry member #90
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    Fort Worth Tx.

  4. #4
    Thanks Ed and gsjohnson, I will start with those areas and report back. The hoses that connect the fan shroud to the heat exchangers are very old and brittle, one with a small hole...would this have any effect?

  5. #5
    Senior Member
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    Quote Originally Posted by Red69T View Post
    Thanks Ed and gsjohnson, I will start with those areas and report back. The hoses that connect the fan shroud to the heat exchangers are very old and brittle, one with a small hole...would this have any effect?
    Not really related.

  6. #6
    Senior Member VintageExcellen's Avatar
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    Exhaust leaks cause backfiring on decel, that is the first place to look when having popping only on decel. Study the flanges to the cylinder head, then the flanges to muffler, then look for pin holes or cracks in the pipes or holes in the muffler.

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