Quote:
Originally Posted by Clarke
Update:
With the steel vacuum line (for vacuum advance) disconnected from the back of the carb, I connected my vacuum gauge to the back of the carb and here are the results:
0.8 inches @ 500 RPM
2.0 inches @ 800 RPM
5.0 inches @ 900 RPM
When I tested my vacuum advance the other evening, it started to move at 5.0 inches.
My vacuum reading off the back of the intake manifold (at idle) is consistently 19 inches.
Based on what I provided above, sounds like I'm losing vacuum in the carb?
|
Hello again Clarke!
What you are describing would be the "ported" vacuum connection that TJ has referred to. On some carbs there are multiple vacuum ports, and most notably on GM (Rochester) carbs, there is a vacuum port on the throttle body, and that is the one that the vacuum advance is connected to since at that location you will have full intake manifold vacuum. Since the GMC Big Block V-6's don't use (for the most part) GM Rochester carbs, your best bet is to tap into the intake manifold to get full vacuum to the vacuum advance. Check your carb to see if there is a port in the throttle body that you can hook up to. You mentioned that your intake vacuum is 19 inches at idle which is good, and if you can get that full vacuum to your vacuum advance, your engine will purr in appreciation!
