Forgive me if this isn't the right forum, but what should the black tee in the middle of the picture go to? Or should it be capped? It's the PCV line before it gets to the carb. Is it stock or something someone did. When I bought the car, it already had the Edelbrock intake and 1406 on it, so who knows what was done. I hooked up a vacuum guage and tuned the carb until I got maximum vacuum. Then if I plug this tee with my finger, it drops some. You can hear it sucking in air when the car is running, so I figured it would be considered a vacuum "leak" and you would get more vacuum with it closed, but I guess not.

Thanks in advance!

 

The plug on the firewall side of the tee looks like either 1) the vacuum line that was supposed to go to the MAP sensor, or 2) the vacuum line that was supposed to go to the heater diverter valve. Either way, doesn't look like it's running to a PCV valve anyway, is it?

What year car, what motor was it originally? Is there a PCV valve hooked to it somewhere? Is there a heater diverter valve?

Cap it for now - it is a leak that will hurt performance.

 

I'm sorry, should've mentioned that. It's an 82 LG4 T/A. If you follow from the tee, it runs to another tee where it hooks onto the port on the carb, then also continues to a plug that goes into the front, driverside valve cover. I thought it would hurt performance as well, but don't you want as much vacuum as possible? Using a guage, I'm right at 20hg with it uncapped, and it drops once capped. Adjusting the idle screws won't get the vacuum back to where it was.

Thanks again!

 

That's a factory hard plastic vacuum line. Would be nice to know where it goes. It could be for the vacuum reservoir of the HVAC system (to move the flappers and doors under the dash when you change the selector on the dash between heat, vent, defrost, etc.). If it's that, you still need it hooked up to a full manifold vacuum source if you want your HVAC controls to work properly.

If it's something like the VAC sensor line, you won't need it hooked up since you've gone away from computer control anyway (by isntalling a non-computer controlled carb).

Your vacuum readings are rising when you uncap it because the vacuum leak is raising your idle RPM (like having the throttle cracked open a little further). Cap it and reset your idle speed and mixture screws again.