Vacuum leak - Smooth idle

[srwilson]

OK, so I'm a little confused here. I just swapped my intake and carb on my 79 from a dual plane intake to a single and a 32adf carb to a 34adf.

After the upgrade I was able to achieve a smooth idle by adjusting the timing and air mixture. However, during the process I also found the Vacuum advance module is bad. (you can suck on it and pull air right through). So I know it's loosing vacuum. But the thing that confuses me is when I plug the V.A. line the car barely idles, unplug the line and the idle smooths back out. I've tried to adjust the air mixture to smooth it out while it's plugged but it never gets back to the smoothness of the unplugged state. What am I missing?

I got a couple others questions.

On the 34adf I see only one vacuum port; it's at the front base. What is it for? Did it go to the carbon filter? I have it plugged right now. Is that OK?

On the 78 single plane intake I have one large dual vacuum port: one side plugged and the other side going to the Brake booster. And also a much smaller single vacuum port that I had running to the V.A. on the distributor. Does that sound right? All my smog items have been removed I should say.

[bradartigue]

OK, so I'm a little confused here. I just swapped my intake and carb on my 79 from a dual plane intake to a single and a 32adf carb to a 34adf.

After the upgrade I was able to achieve a smooth idle by adjusting the timing and air mixture. However, during the process I also found the Vacuum advance module is bad. (you can suck on it and pull air right through). So I know it's loosing vacuum. But the thing that confuses me is when I plug the V.A. line the car barely idles, unplug the line and the idle smooths back out. I've tried to adjust the air mixture to smooth it out while it's plugged but it never gets back to the smoothness of the unplugged state. What am I missing?

I got a couple others questions.

On the 34adf I see only one vacuum port; it's at the front base. What is it for? Did it go to the carbon filter? I have it plugged right now. Is that OK?

On the 78 single plane intake I have one large dual vacuum port: one side plugged and the other side going to the Brake booster. And also a much smaller single vacuum port that I had running to the V.A. on the distributor. Does that sound right? All my smog items have been removed I should say.

Reading from the bottom to the top, you have your vacuum advance connected to the manifold, which isn't the right place to connect it, and its leaking. It is not a very big leak but is enough to produce a lean idle. Fix the distributor. Cap the connection, then set the idle, then connect it in the right place, which is on the carburetor itself: http://www.artigue.com/fiatcontent/carb ... orting.pdf - it should have a small pipe where it says "connection for Vacuum advance" - if not you can send it somewhere to be tapped, try to do it yourself, or ask your vendor why a $160 Chinese knock-off has the port and the $600 new one you bought does not. There is no good way to compensate for the lack of the port except by using a different distributor (e.g. Marelliplex or one of the new replacements).

The dual vacuum port was for the brake booster and the idle electrovalve, which you do not have, therefore the non-brake side of the thing can be capped off.

[srwilson]

Thanks, Brad, I appreciate the help.

I've got a new vacuum advance module on the way. I'll take a look at the carb to see the spot you mention. I think I have someone that might be able to tap it out, but I'm not sure where to get the port to put there.

Maybe a new distributor would be easier...