Engine runs smoother with open vacuum line.
 

So what does it mean when I open my wiper vacuum line and the engine idles smoother? Wrong timing? Points not gapped right? Hopefully not a valve problem!

Re: Engine runs smoother with open vacuum line.
 

Sure sounds like an over rich condition could be caused by a number of things like ignition, carburetor.
I would doubt its a valve problem but a compression check wouldn't hurt.

Re: Engine runs smoother with open vacuum line.
 

Probably the carb idle circuit is too rich. If you have an air cleaner check that first, then try adjusting the idle fuel mixture next -

Re: Engine runs smoother with open vacuum line.
 

It means you are running leaner.

Re: Engine runs smoother with open vacuum line.
 

Re: Engine runs smoother with open vacuum line.
 

If that works, it means he's not on the idle jet at idle. If you are on the idle jet then the GAV won't do anything, you'd need to adjust the idle screw. See the diagram here under Idle.

Re: Engine runs smoother with open vacuum line.
 

I read it as he pulled the hose off and car runs better. Might try closing the idle jet needle down then open 1 1/2 turns to start with. Pulling the hose off would be like a vacuum leak, to run right you would need to increase the fuel to air mix. The idle jet needle may be closed too far so with the hose back on is running rich. Once the hose is pulled off, allowing more air, the mixture is correct. The idle jet is an air/fuel adjustment. The more open it is turned, the more air is pulled in making a leaner mix. It may just be screwed in to far now making a richer mix.

Re: Engine runs smoother with open vacuum line.
 

It is common for all engines to do that. For one thing, the idle speed goes up.

Re: Engine runs smoother with open vacuum line.
 

Hmm. The GAV impacts the flow of gas into the well from which both the cap jet and the idle jet draw their fuel. I see a difference in the idle when I play around with the GAV. Open too much and the idle will surge a little and I smell unburned gas in the exhaust.

Re: Engine runs smoother with open vacuum line.
 

Carb adjustment is for air not fuel. closed is full rich. 1 1/2 to 3 tirns open is aprox. where is your's set?

Re: Engine runs smoother with open vacuum line.
 

Attachment 458881

The GAV adjusts only the supply seen here in green, which boosts the fuel flow to the cap jet. The idle jet's inlet from the fuel bowl is higher, so it's not affected by the GAV. If your GAV is affecting your idle, maybe you're not 100% on the idle jet to begin with?

Re: Engine runs smoother with open vacuum line.
 

Make sure you don't have any air leaks besides the one you made, LOL> then you can set the idle speed correctly first. Typically, carbs have overlap between circuits (think about how the engine would run if that transition were not true) so one circuit will normally affect the adjacent circuits to some degree initially, which means having the GAV affect idle a bit should be OK (IMO). In any case, the best way to set the idle mixture (on just about any machine) is to do it while it is running. With an air-bleed idle needle, the SOP is to turn the screw in until the engine runs rough (rich), then back it out until it speeds/stumbles ..in between is where you want to be (with a little trial and error) to get it right on. Check it out while driving also, so you get the best adjustment possible. In my experience, the tiniest rich at idle makes for better pulling power off bottom (all jetting can change some due to altitude and temperature).

Re: Engine runs smoother with open vacuum line.
 

You will get the same affect, increasing the engine speed, when you have a Wolf Whistle and pull it open... the engine speeds up... as you have introduced more air, just as the OP is experiencing.

Re: Engine runs smoother with open vacuum line.
 

Thanks to all. I know where to focus now. Alexiskai - Carburetor basics is great resource....THANKS. Redmodelt - great explanation. I had never really thought about what the effect is on fuel/air mix when vacuum line was open. I have an 85 big block Ford PU that reacts the exact opposite the A. That is, when a vacuum line is disconnected the engine runs real rough on idle. Guess that's why I was having problems figuring this out.