[Jack4]

Hi All,
Can you please help me with my carb.
It has 3 ports on the front, the Timed port (passenger side), PCV port (middle), and Manifold port (drivers side).
When a vacuum gauge is used, the Manifold port is acting the same as the Timed port, WHY???
Both have no vacuum at idle, and then increase the same amount as the revs are increased.
The PCV port has a vacuum of 16 at idle and increases as the revs increase, as you would expect.

From looking at Youtube videos, I thought the Manifold vacuum (which is at a lower level than the Timed port)
was supposed to have vacuum at idle and decrease as the revs are increased. But its not.
Can you please help me understand what's happening. Is this normal for this carb, surely not!
Many thanks,
Jack

 

[BogiesAnnex1]

While in my feeble memory it might be I recall the competition version may not have had full time vacuum advance at that port under the assumption that competition engines with big cams didn’t use vacuum advance. I pretty sure just drilling it out will restore functionality, but trace out the passage before committing to that. But I seem to remember back in the good old days these were either capped or hose connected together.

You can always tee the hose to the PCV port or directly off the manifold.

Bogie

 

[Jack4]

Yeah its T'd off the PCV valve, that was the original setup of the vacuum advance on the engine.
I was just curious about why the 2 ports were acting the same way. Both zero vacuum at idle.
Has any of you others guys got any ideas or more information??

 

[RWENUTS]

Passages not drilled out, drilled wrong or wrong gaskets will cause that.
Or sometimes a bent throttle plate.

 

[Jack4]

Passages not drilled out, drilled wrong or wrong gaskets will cause that.
Or sometimes a bent throttle plate.

so do you think, it is meant to be like that, or how the engine builder wanted it?
Or how this type of carb is designed? Seems strange to have it this way.
What would happen if it was an automatic, then your modulator would not work properly, right?
The engine shop must have known it was this way, that's why they T'd into the PCV port hose.
As you can see in the picture attached, there is definitely a difference in the level of the 2 ports.
Just makes no sense to me why both have the same vacuum.

 

[RWENUTS]

It’s a 30-40 year old carb. Anything could be changed.
If you need more manifold vacuum ports just find a vacuum tree and put it in an intake runner. Usually one behind the carb. Could plug vac modulator into it.
‘Here’s but one example.

Camaro Intake Manifold Vacuum Fitting, Power Brake Booster, Threaded Port, With 3 Extra Vacuum Ports, 1967-1969

Intake vacuum fitting with threaded power brake booster take-off and three vacuum hose take-off. Plated.

www.camarodepot.ca