weber: vacuum advance info

[dlb]

there's been much discussion about how to hook up vacuum advance when running a weber 32/36 on our beloved tercels. i've been looking into it a lot and found a great article on the topic, as well as a pertinent weber diagram.

http://performancecarbscience.com/weber ... onversion/

here's the long and short of the article. assume you are running a lean air/fuel mixture and have your vacuum advance connected to the manifold. now, lean mixtures take longer to burn. to compensate for this, the vacuum supplied by the manifold during idle and hwy cruising advances the timing, which allows the air/fuel mixture more time to burn--so this is good. vacuum advance is not needed during acceleration because the mixture becomes richer then and thus burns faster. during acceleration, manifold vacuum drops and no longer advances the timing, giving the mixture less time to burn, which is precisely what you want for a rich mixture. i'm simplifying like crazy here so take a minute and read the article.

in conclusion, if you like to run a lean air/fuel mixture (which you probably do unless you're racing your stock 3A tercel--ha!), you want the vacuum assist from your distributor connected to the manifold vacuum port. if you race and use a rich air/fuel mixture, then you might consider ported vacuum.

for those interested in trying out ported vacuum, here's a diagram that displays two ports that can be used for ported vacuum on the weber 32/36:



hope that helps everyone!

[ebayollis]

just posting so i can track it

[ARCHINSTL]

I wonder where I am...manifold vac to front upper canister tube (rear blocked) and carb ported vac to lower canister tube.
My reasoning is that's the way the Federal and Canadian versions were setup from the factory. I've noticed nothing amiss, whether during the initial setup or the recent timing change to 10° BTDC (and resetting the idle mixture)
Tom M.

[deejay1272]

In conclusion, if you like to run a lean air/fuel mixture, you want the vacuum assist from your distributor connected to the manifold vacuum port.

Thanks for the information, David. I've been struggling with this lately!

One question: When you say "manifold vacuum port," you are referring to the port on the Weber that is labeled "vacuum advance port" in the image that you've provided, right?

[dlb]

no deej, manifold vacuum refers to the ports mounted on the intake manifold, just in front of the carb. ported vacuum refers to the EGR and/or vacuum advance port.

the manifold vacuum port is in this pic on the far upper right. hook the vac adv. to one of the ports and plug the other one.

[deejay1272]

So then the port on the Weber 32/36 that is labeled "Vacuum Advance Port" goes unused? (Sorry - I'm pretty confused right now).

[dlb]

So then the port on the Weber 32/36 that is labeled "Vacuum Advance Port" goes unused? (Sorry - I'm pretty confused right now).

that's correct. if you read the article i posted the link to it explains it pretty clearly. give it a read, it helped me understand what's going on with dizzy advance a lot better.

[deejay1272]

Ok - I read the article in greater detail and this is starting to make much more sense to me. As I understand, the "vacuum advance port" on the Weber 32/36 provides ported vacuum, which corresponds to ported spark as described in the article. This is meant to reduce reduce hydrocarbon emissions, but the unfortunate end result of using ported vacuum is increased exhaust gas temperature (due to “lighting the fire late”) to improve the effectiveness of the “afterburning” of hydrocarbons by the air injected into the exhaust manifolds.

"...As a result, these engines [with ported vacuum advance] ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle – cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it."

Thus, to get a more consistent idle and more fuel economy in low load situations (idle and steady hwy cruise), we need to hook the distributor vacuum advance up to the manifold vacuum port (which in the case of the T4WD is the "gas filter" that David pointed out above).

Thanks for enlightening us, David! I'm going to install my new dizzy vac advance, connect to the gas filter and let 'er rip!

[dlb]

glad i was able to help! i was wondering about this for a long time myself and know others have asked so it should prove useful to our community here.

[danzo]

There are three vac tubes coming from the vac advance unit on my car. Where does each one go? Please forgive my confusion as I haven't actually slapped the weber on yet.

[Petros]

only one of the vac ports advances the spark on the distributor. You want the one on the end of the diaphram, it only advances the spark timing, check by sucking on the port and you can see if it advances or retards the backing plate.

The other two are there to retard the spark under certain driving conditions to reduce emissions, all harm economy and performance, so I would just cap those off.

[SynthDesign]

Great writeup!

[ebayollis]

so the distributor advance hooks up to the gas filter?
it hooks up where the red arrow in the following pic is?

[deejay1272]

so the distributor advance hooks up to the gas filter?
it hooks up where the red arrow in the following pic is?

Yep - that's right. Connect either of the two gas filter (manifold vacuum) lines to the vacuum port on the end of the dist vac advance. Cap off the extra gas filter port. Lean out fuel mixture (don't touch the mixture screw on the OEM carb, this is factory set). Advance timing as much as you can without introducing ping. Record what your timing is for future reference (in case you need to adjust to pass smog tests).

[ebayollis]

dont mean to sound stupid but how do you advance your timing?