Carter WCFB Issue

[ScottMH]

Hello everyone, I am working on a 1963 Corvette, 327 (fresh rebuild), 4 speed. The orginal WCFB 4 barrel was rebuilt by a specialist and I am having a strange issue that I would like to run by everyone here. I drilled and tapped the 90 degree fitting that the PCV Threads into on the back of the carb. I installed a hose barb fitting so I can attach a vacuum gauge for tuning. I noticed that the Vacuum gauge read 0 while running so I thought maybe there was a problem with the PCV. I ordered a new PCV and installed it and it had the same vacuum reading of 0. From there I decided to Crimp the PCV Hose shut. Once the hose was crimped shut the vacuum gauge began reading. I tuned the carb then released the clamp on the PCV hose. Idle speed came up and vacuum returned to 0. So, I retuned the Idle mixture screws with the PCV hose open hoping to see a change in vacuum readings, which I did not. Currently the engine is running nicely, Timing is at 15 at idle and 37 at 2500rpms. However, I still have a 0 reading on the vacuum gauge, revving the engine also yields 0. I put my hand over the oil fill tube and plugged the hole on the oil fill tube for the breather line. Vacuum reduced to about -1, the idle speed did not change. I put my hand over the carb to check mixture, idle speed and quality did not change. I have never worked on a car with a WCFB and I have never seen a issue like this. I do have experience with Holleys (stock and aftermarket) Edelbrocks and 60-80s Quadrajets. Is my issue I am trying to pull a vacuum reading where there simply is no vacuum? Is it possible the new PCV is also bad? Am I just missing something entirely?

Thank you in advance.
Scott


I should also not that after I retuned the carb with the PCV hose uncrimped I decided to crimp the hose to see what would happen. The engine immediately died.

 

[Tom Bryant]

WCFB Vacuum Port

Hi Scott and welcome to the Corvette Action Center.

To answer your question, yes there is no vacuum there or very little. The pcv is a specific size hole that allows the engine to draw unburned gasses from the crankcase and run them back through the engine to burn them. It's also the only relief for crankcase pressure so, depending on the condition of your engine, you can easily have pressure in this line from a little to a lot when the engine is running. The check valve in the pcv that rattles when you shake it is to prevent flame from traveling backwards into the crankcase in the event of a backfire. Simply put if the valve rattles then it's good.

I have a carb just like yours on my bench in front of me and the only vacuum port, other than the pcv fitting, is the one on the front for the distributor vacuum advance. This is a full time vacuum port that draws from an orfice in each primary ventury below the butterfly valves. You can unplug the distributor vacuum advance can and connect your vacuum gauge to this line to the front of the carb to make your carb adjustments. Start with your mixture screws open about 1 1/4 turns from seated.


Tom