Thread: sluggish down low! help!

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Originally Posted by firebird77clone

You might also check the vacuum source the line comes off. Best bet is to use a source directly off the intake. If you are using a source off the carb base, it may or may not have vacuum at idle. The carb nipple which has vacuum at idle is the one you want, and is referred to as 'ported'.

firebird, your theory is correct, but you have the incorrect term. Ported or "timed" vacuum ports are above the throttle plates and have no vacuum at idle.

Originally Posted by Henry Rifle

firebird, your theory is correct, but you have the incorrect term. Ported or "timed" vacuum ports are above the throttle plates and have no vacuum at idle.

Not always the case Jack, some carbs have internal passages that allow manifold vacuum to be seen with a port that is above the throttle blades. Idle the motor. Place a small piece of paper on the port. If it gets sucked down against the port, it's origin is manifold vacuum. If it will not stick to the port, it is a ported vacuum source.

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