should i see vacuum on the distributor at idle?

1177 Views 11 Replies 6 Participants Last post by The Greek, Jun 13, 2009

tempoffroad

Discussion Starter · Jun 11, 2009

i was checking timing on my 66 2v with a 289 and was wondering if i should be getting vacume at idle on the distributer. i checked timing and set idle with vacume line off and then as soon as i hooked the line up the timing jumped up about 10*. this is a stock 2 barrel carb.

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rocky289

· #2 · Jun 11, 2009

If the vacume line is conected to the spark advance port at the carb it shouldn't get advance until you open the throttle.
If the line is connected directly to manifold vacume it will be advanced & will retard when you open the throttle.

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youknowme

· #3 · Jun 11, 2009

The word is VACUUM. 'Vacume' is not a word.

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tempoffroad

Discussion Starter · #4 · Jun 11, 2009

the line is connected to the carb on the passanger side bottom. on this 2barrel it is the only port that i can find. I am getting vacume at idle with the blades closed. its not much but some. its enough that it is increasing timing about 6-8* at idle then it increases as i increase the throttle. would a carb rebuild fix this? i think that air may be bleading by the throttle blades or a gasket.

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hypostang

· #5 · Jun 12, 2009

The vacuum port needs to be ABOVE the throttle plates ...ported vacuum
What kind of carb are you running ?

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rocky289

· #6 · Jun 12, 2009

youknowme said:
The word is VACUUM. 'Vacume' is not a word.

That's what my wife would say.

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tempoffroad

Discussion Starter · #7 · Jun 12, 2009

this is on the stock 2 barrel. i think that its an autolight 2100. i have looked everywhere for another port and their is not one. at least on the carb anyway.

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The Greek

· #8 · Jun 12, 2009

Your engine is fine with the vacuum advance connected to full manifold vacuum where there is vacuum to the vacuum advance canister on the distributor when the throttle is closed.

The timing does NOT retard when the throttle plates are opened. It will continue to advance. There is much debate as to which connection to use. Timed vacuum, where the connection is made so that there is no vacuum with a closed throttle, started being used as an attempt by the manufacturers to reduce hydrocarbons and does not necessarily make your engine run better.

I have my performance built 5.0/302 hooked up with full vacuum. It will smooth out the idle, increase fuel milage and make the engine run cooler. It is explained at the following web site. Even though it discusses the application with Chevy engines, the principals are the same no matter who makes the engine.

www.lbfun.com/Corvette/Tech/vettetech.html Scroll down and click on to "Timing and Vacuum Advance" then click on to the article "Vacuum Explained" by Lars Grimsrud.

This article explains why you should have the vacuum advance connected to full manifold vacuum, the way that your engine is hooked up.

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tempoffroad

Discussion Starter · #9 · Jun 12, 2009

Thanks that was the best sight and answered all my question i have spent an hr reading all that was their. Cant tell you enough how much that helped me.

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mustang402

· #10 · Jun 12, 2009

Hey Greek,
You are correct and great info supplied as always. I enjoyed the read as well.:bigthumbsup

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rocky289

· #11 · Jun 12, 2009

Excellent article Greek.
Anyone reading & understanding that, should have no problems.

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The Greek

· #12 · Jun 13, 2009

I have a lopey cam and an automatic. Hooking up the advance to full manifold made driving at low speeds or in traffic much more tolerable for me and the engine.

I've read a few of Lars Grimsrud's articles and I'm impressed with his knowledge and his ability to transfer that to understandable written words. I appreciate that you all took the time to read the article.
Thanks :bigthumbsup

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