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Wed Dec 28, 2016 11:56 am

Hello,
I have just acquired a vacuum gauge tester seeing how it could be used to tune the mixture.
In a stock air cooled VW carburetor (type 1) and manifold setup can you use the vacuum port for the distributor as a vacuum signal source for the gauge, or do you need to have (or drill) a separate vacuum port in the manifold?

Thanks.

Wed Dec 28, 2016 12:05 pm

I've not done it this way but I guess you'd need a vacuum takeoff above the throttle plate of each cylinder.
Would be interesting to here what people have to say about this method :)

Wed Dec 28, 2016 1:24 pm

Sharing the port should be fine but a vacuum gauge is typically used to sync multiple carbs air. How are you planning to use it to tune the mixture?

Wed Dec 28, 2016 1:32 pm

Well, that's the thing - it would appear that you can diagnose much more things (including idle fuel mixture) with a vacuum gauge.
I have just bought mine and I am very curious about playing with it.

Example: http://www.superchevy.com/how-to/45638/
http://www.studebaker-info.org/Tech/vacuum/tvg.html

Wed Dec 28, 2016 1:49 pm

After I posted my reply I went ahead and Googled similar sites. In the past with my old V8's I did use a vacuum gauge once in a while but those are mostly a visual tool as apposed to using the Tack, your ear or now the snail when syncronising Dual Dellorto's or Webbers. It's also very common to sync 4 cylinder motorcycled with 4 gauges and 4 vacuum tubes. One fore each carbs vacuum port. Like some of those articles say it is a very accurate tool if you know how to use one but most hobbyists don't own one. I can see how it would easily be used for synchronizing multiple barrels and for lean best idle but not Wide open throttle mixture. Which is where I was thinking. Certainly small changes that effect idle speed will be visible on a vacuum gauge but with many cars having a Tachometer I think using that is more common. I supposed the gradient on a vacuum gauge could be more micro accurate than a Tach to see the vacuum (idle speed changes). Should be fun to play around with.

Wed Dec 28, 2016 1:56 pm

https://actron.com/sites/default/files/pdf_english_16176.pdf

Thu Dec 29, 2016 12:44 am

yamaducci wrote: I can see how it would easily be used for synchronizing multiple barrels and for lean best idle but not Wide open throttle mixture. Which is where I was thinking. Certainly small changes that effect idle speed will be visible on a vacuum gauge but with many cars having a Tachometer I think using that is more common

Well, I initially bought the vacuum gauge (it is actually a compound pressure and vacuum unit) to test the fuel pump pressure :)
But since I have it i might as well explore a bit with it.

It could be useful to tune up the idle mixture, indeed, especially in a dual carb setup such as the typ3 that I have.

PumaVW79 -> thanks for the link. The instructions are similar to those on my vacuum gauge's documentation.

However, my initial question remains:
Can you use the vacuum port from the distributor advance to do these tests? I am talking about stock style distributors from type1 engines.

Thu Dec 29, 2016 1:56 am

Komissar wrote: However, my initial question remains:
Can you use the vacuum port from the distributor advance to do these tests? I am talking about stock style distributors from type1 engines.

Per instructions:
5. Using the hose supplied, connect the Vacuum Gauge to a source of manifold vacuum. This may be a fitting on the carburetor below the throttle plate, or a fitting in the intake manifold. See Figures 2 and 9.

You should check if the the the vacuum pickup orifice in your carburetor is not placed above the throttle plate (exposed to venturi vacuum instead of manifold vacuum).

Thu Dec 29, 2016 3:41 am

Komissar wrote:
However, my initial question remains:
Can you use the vacuum port from the distributor advance to do these tests? I am talking about stock style distributors from type1 engines.

According this paragraph on the instructions the conclusion is yes
But you need to perform the checking mentioned in my previous post whether your reading is below 10 in.

The general condition of an engine is indicated by one of three possible gauge readings: A.(Figure 3) A reasonably steady vacuum reading of 4 inches or more on emission controlled engines, and 10 inches or more on non-emission controlled engines (pre-1968) indicates correct engine vacuum. Readings may vary considerably on different engines, but should not fall below these minimums. (See manufacturer’s specifications).

.emission controlled engines = vacuum pickup orifice above the throttle plate
.non-emission controlled engines = vacuum pickup orifice below the throttle plate