Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Dieseling

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Chevynation:
It’s almost like it’s a bleed off port or something. Not sure how they routed vacuum lines for the original vehicle. The carb only has three ports. The port on the front for pcv, the port on the passenger side which I thought was full manifold vacuum, and the port on the driver front which should be ported. I didn’t test that one but it didn’t appear to be manifold the way it was routed. I don’t have any ports on the baseplate. My manifold has a hole behind the carb so I installed a fitting for my power brake hose connection. Same way it was from the factory on my car. Do I have to drill the baseplate for a manifold vacuum port?

Kenth:
Now you are "robbing" air from the idle bypass source, that´s why you see low vacuum in the side manifold vacuum source.
Instead of cutting the gasket you should have drilled the hole a bit further to the next location in float bowl. Then you will get full vacumm signal in the side manifold port, and a fully functional idle bypass air.

Chevynation:

--- Quote from: Kenth on October 21, 2023, 02:03:22 AM ---Now you are "robbing" air from the idle bypass source, that´s why you see low vacuum in the side manifold vacuum source.
Instead of cutting the gasket you should have drilled the hole a bit further to the next location in float bowl. Then you will get full vacumm signal in the side manifold port, and a fully functional idle bypass air.

--- End quote ---
I’ll get a new gasket. You’re a genius. That next port would’ve been perfect so I’ll drill to that hole.

Chevynation:
I might just epoxy the vacuum port hole thats currently exposed from shaving the gasket and drill to the next hole like you said so I don’t need a new gasket at the moment. However, if I need a new gasket should I shave it so that the bypass hole on the base plate is fully showing and not just maybe 1/4 of the hole. The majority of the gasket is just covering the hole. It is fine on the main body and the driver side hole is centered perfectly on the base plate. I would’ve thought it shouldn’t be blocking the hole. Is this not considered a restriction and should be left alone? Thanks again.

Kenth:
No need for epoxy.
A new gasket will cover the unwanted hole and solve the idle bypass issue as the slotted hole in gasket acts like an air channel leading air to were it´s needed.

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