Re: Vacuum Advance w/ Weber Carb

[farna@xxxxxxx]

There was a big discussion about vacuum advance and where to get it on hotrodders.com that involved an automotive engineer. What it came down to is for power and economy the vacuum advance shoud come from the MANIFOLD like all the older cars do, NOT PORTED. Ported advance isn't as strong, so advance comes in later and not as much, which causes power and economy loss compared to manifold vacuum. It was moved there to reduce NOX emissions at idle and low speeds since there isn't enough vacuum to pull the advance much. Once the engine fully warms up, there is less NOX produced. That's when manufacturers started using CTO valves to switch the vacuum source from ported when cold to manifold when fully warmed up. The CTO is a temerature controlled vacuum valve, screws into the water jacket on the left side of AMC sixes, under the exhaust manifold. I don't know where it is on late mode V-8s. 

It's a bit odd that there is so much vacuum at the Weber carb port. In any case, I'd cap it and use a source off the manifold close to the center -- at least until emissions testing came around. Don't piggyback off the brake booster though! There are usually several plugs in the intake, remove one and screw in a hose barb available from auto parts stores and even Lowe's. Should be standard pipe threads, IIRC. 

--
Frank Swygert
Publisher, "American Independent 
Magazine" (AIM)
For all AMC enthusiasts
http://farna.home.att.net/AIM.html
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original message---------------------------------------------
Date: Sun, 15 Jan 2006 19:56:36 -0800 (PST)
From: Tom Jennings <tomj@xxxxxxx>
To: mail@xxxxxxxxxxxx
Subject: Re: Vacuum Advance w/ Weber Carb
Message-ID: <20060115194532.D77081@xxxxxxxxxxxxx>

On Sun, 15 Jan 2006, Todd Tomason wrote:

> Anyone else using a Weber two barrel on their 258?  I have one of the K551
> kits installed on my 83 Spirit.  I was curious how you connected the vacuum
> advance.  I currently have it connected directly to the ported vacuum on the
> passenger side of the carb.  I'm getting a rough idle after the engine has
> warmed up, and I'm wondering is this is the problem.  Is there a better way
> to hook it up?

I have one, a 32/36 DGEV. Very happy with it, except -- the vacuum
port for the vacuum advance! It seems to have vacuum on it at
idle.