I'm flying blind on this.
Before anyone asks, I don't know what cam I have.

This is a 1970 Rocket 350.
1970 heads, with upgraded components. Pic at bottom.
I have a Eddy Performer RPM intake and a Eddy 1407 750cfm carb on it.
I'm trying to tune this sucker for maximum benefit here. It feels great, but I want to be sure.

I'm trying to use a vacuum gauge on the timed and full vacuum ports.
On the timed (pass side front) I am reading a PRESSURE reading instead of vacuum.
On the full (drivers side) I am reading ~7 inches of vacuum.

What am I doing wrong and what should I be reading ??
I thought ~13 inches of vacuum was my target.

I'm not sure what my timing is set at just yet. I haven't looked.
I have to go search for those settings again.

 

I thought on a healthy stock engine, 18-20 is ideal. I know you don't know what cam you have, but can you describe the idle characteristics? Is it really lumpy or smooth? I believe you can play with the idle mixture screws to get a higher vacuum reading.

 

I did play with the idle mixture screws on both sides.

I didn't get anything better then a 7" of vacuum. It's not racey, it sounds like it's fine to me.
Maybe I will go do a video to show what I'm talking about so people can hear it. No tach hooked up.
So I don't know my RPM......maybe I should hook up the tach too.

I watched the Edelbrock video and tuned the carb like they showed. You tighten the screws down until
you notice the carb start to "Choke" then you back them out a 1/2 turn or so. This is for the LEAN setting.

If you go the opposite way, that is for the "RICH" Setting.

 

Take a reading from the intake manifold, and find out what the initial timing is, then post that info.

 

Carb Idle Adjustment (Old school)

Use Tach and adjust Idle screws to obtain Highest Engine (RPM). Turn a screw ssslllllooowwwllllyyyy and then wait for Carb to adjust to modified fuel flow. Turn no more than 1/8 turn, (1/8 of a complete circle). Do one barrel (side) first, then the other, then check the first again.

The directions to turn back the screw are more for HC reductions and to reduce the gas burnt during idling. For performance tuning you just go for high RPM, cause you don't care about amount of gas spent.

71Cutlass is correct, manifold vacuum should be taken from Intake manifold port. I blew-up your pic, (so I can see it), and connecting the vacuum gauge to the PCV port, (the big middle one) should give you a 'close enough' manifold vacuum reading.

Now for the two other ports. I would 'guess' that the port that 'has pressure' is for your Distributor. It will not advance Distributor Timing until you open throttle. The other port that has low vacuum is a general purpose vacuum port for accessory, wipers or whatever. If you are not using that port plug it.

When you open throttle you should see immediately vacuum in Distributor Port vacuum. If you don't you got the wrong port. You will see a drop in vacuum pressure in the PCV port and for the other port (general purpose) depends on the design the Carb, so I don't know.

I would hope the Video would have explained all of that. If not, it's not worth much.

Nice looking heads. Hey lets us know what the Intake Manifold Vacuum is when you get it.

 

There is no "ideal" number. The only "ideal" is a steady needle at a given RPM and load.


Edit: Changed "during the test" to "at a given RPM and load.

Norm

 

Perhaps Norm's thinks if intake manifold vacuum was a steady 2 psi things would be great.

Ace, one additional note that I did not pointed out, once you reach the highest RPM reading on the Tach meter, continually turning the screw will not help performance.

So, when you hit the Highest RPM do the very fine adjustments by turning the screw back in and out in very small amounts - just to make sure you are at the exact point when you reached the Highest RPM [like 1/16 of a turn or even less].

Years ago when a car of mine required Smog testing, I did a Carb rebuilt and adjustment just prior the required the Test. I took it down to the local Service station, because I wanted to see how it would do before the actual Test. The mechanic hooked up the Exhaust Gas analyzer and the Idle screws only required a very, very [very] small amount of adjustment to achieve the most efficient gas air ratio.


The Exhaust Gas analyzer is the best method, but most people don't, (sorry typo in original reply), have the 5 or more grand to buy one. The Tech meter method is a close second.

 

I made the correction. Thanks for calling it to my attention.



Since Ignition advance has a direct effect on intake manifold vacuum,
it would be the logical place to start.

Norm