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Old May 13, 2013 | 10:12 AM
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I am getting a little less than 15" of vacuum on the manifold @ idle. Is this within normal range?
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Old May 13, 2013 | 10:50 AM
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Originally Posted by genuine1980
I am getting a little less than 15" of vacuum on the manifold @ idle. Is this within normal range?
Yes as long as it's pretty much steady reading with no big fluctuation of the needle. I use to have 10" vacuum with a big cam. I've advance the base timing extra 4 degrees and running close to 16 inch now.
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Old May 13, 2013 | 11:18 AM
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Originally Posted by jackwabbit703
Yes as long as it's pretty much steady reading with no big fluctuation of the needle. I use to have 10" vacuum with a big cam. I've advance the base timing extra 4 degrees and running close to 16 inch now.
Yes, my car has a large cam. I am at about 15 with no jumping. I achieved this as the highest idle vaccum I could get while adjusting the carb fuel/air mixture. Car seems to running better, smoother, and much smoother idle.

The next thing I was going to do is check/adjust timing. If I need to adjust the timing, I was going to re-check the fuel/air mix to see if I can do better.

Thanks!
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Old May 13, 2013 | 11:34 AM
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Originally Posted by genuine1980
Yes, my car has a large cam. I am at about 15 with no jumping. I achieved this as the highest idle vaccum I could get while adjusting the carb fuel/air mixture. Car seems to running better, smoother, and much smoother idle.

The next thing I was going to do is check/adjust timing. If I need to adjust the timing, I was going to re-check the fuel/air mix to see if I can do better.

Thanks!
Yes, I mentioned this in my post on your other thread, whenever you make any changes, you need to go back and optimize the idle air/fuel ratio. Rule of thumb: adjusting idle mixture is always the last tuning step. Unless you are experimenting with tire pressure, or something!

Scott
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Old May 14, 2013 | 07:17 AM
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Originally Posted by genuine1980
Yes, my car has a large cam. I am at about 15 with no jumping. I achieved this as the highest idle vaccum I could get while adjusting the carb fuel/air mixture. Car seems to running better, smoother, and much smoother idle.

The next thing I was going to do is check/adjust timing. If I need to adjust the timing, I was going to re-check the fuel/air mix to see if I can do better.

Thanks!
Once you get the highest vacuum reading (or highest idle speed, if using a tach), richen the mixture up a eighth turn or so. Due to unequal fuel distribution, some cylinders run a little leaner than others, so you want to richen it up a hair, so those lean ones still get what they need.
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