In my 70 I am running a 350 with a comp cams 507/510 lift cam, edelbrock victor port matched intake, demon 750 speed demon, AFR 195 heads ported, pertronix flame thrower dist. with a msd 6al box. This weekend I was trying to tune it a little better, but could not get it right. I unplugged my vacuum advance, and tried timing it but to get it running best, i had it timed at about 18 degrees, which put my total timing at almost 50 degrees. Does this sound excessive, or am I just imagining that it runs better at this timing?
Another problem I am having is the vacuum, the motor only is putting out about 5" at idle, which makes my brakes barely work. I have a canister to hold vacuum, but it is not enough, is a vacuum pump my only answer, or will I possibly get more vacuum with the engine tuned better? Any help would be great as I am still learning and any tips are welcomed!

I like to have 18 at idle and around 36 to 38 total. 50 is way to much. Are you sure your balancer has not slipped i have seen that happen alot. What power valves do you have in the carb?

The power valves are the ones that came in the carb, what do you mean the balancer slipping?

Most SBC run best with 36 - 38* total advance all in by 3000 rpm. You might need to modify the dist to limit the advance.
In my Nova I run a 355 10.5:1 with camel humps, isky Z-70 548 lift 304 adv. duration solidcam, with Victor jr, and 650DP holley. My combo yeilds 8" of vacume at idle. I swapped out the original 6.5 power valve for a 3.5, and the idle cleaned up nicely, (no more burning eyes) and the throttle response is WAY better.
My brakes are a little ify at idle, but in a normal braking situation, when you decelerate, the vacume actually increases, and it brakes pretty well.
Your carb probably has 6.5 power valve stock, so if you have only 5" vac., you'll be way rich at idle, and the throttle response probably isn't as crisp as it should be. Figure about half your vacume at idle, and that's the power valve you should have. I'm not sure if a 2.5 is available, but I know 3.5 is. They're cheap, and the local Auto Zone had it in stock. (don't over tighten when you install, and make sure the gaskit seats correctly.)
As for the balancer... it's two pieces seperated by a rubber like O ring. The outer ring on the balancer can actually slip, which will throw off the timing mark.
Hope this helps some

I just bought a 2.5 Power Valve from Advance Auto. They had to order it but it was there the next day. I you get in there before 2pm it will be there by the end of the day. Aleast that what they gentleman told me. I have a Street Avenger 670 and was having the same problem burning rich but the switch to the 2.5 cured that. BTW: I also had 5in of vaccum at idle and in drive. The holley tech recommended the 2.5. The price from Adavnce was $7.99.

As a matter of information, the only way the power valve flows fuel at idle is if the throttle plates are too far open and it is running off the main circuits and not the idle circuit only. Best way to cure this is to open the secondary side until the engine draws enough air to breathe at idle without using the main metering circuits.

But of course, the band aid fix is to use a pwoer valve rated at 2" which will only work at WOT.

SBC seem to like anywhere from 36 to 40 total degrees of timing. If 18 initial gets you 50 total, then you'll need to limit the mechanical advance from 30+ degrees to 20. Then 18 initial will yield 38 total.

70sixspeed was your total * with the vac can hooked? if so then it should be okay provided the vac can gives advance of 10-12* ABOVE 10 inches HG(without heavy load). assuming manifold vac source and not a ported source. There are Many Different schools on this Here is mine if you are interested.
I use a manifold source advance to supplement My initiall base setting This method alows me to have easy cranking a good idle quality and as vac (and advance)goes away It acts as a spark retard at high load and higher rpms. I have my chevelle at a 7* base, 38* total (Mech 31*) under load and a vac cannister that gives me 10* above 10inches HG. so everytrhing hooked up it looks like this: initial idle 17*, WOT 38*, Hwy Cruising 48*.
Milan

On my driver, I have the VA hooked to manifold vacuum. Initial w/o va at 16º, total at 36º. With the VA hooked up, 26º at idle, 46º cruise, 36 WOT. My bracket car isn't much different, 18º initial, 38º total, no VA on the distributor. BTW, the PV has no effect on idle mixture. Even if it is open, the idle mixture is not affected. The only time the PV has any effect on idle is if it is ruptured. Then it is dumping fuel directly into the manifold.

For what it's worth....
From the Holley Web site Troubleshooting tips:

QUESTION I have a camshaft with a long duration and a high lift. It will burn your eyes at a idle. What can I do to fix this?

ANSWER The most common cause is an improperly rated power valve. You will first need to choose the correct power valve for your application. This is covered in another section of the Technical Information Library. When you have a camshaft of this configuration it requires more air and fuel for it to operate efficiently. This in turn requires you to raise your curb idle screw to obtain the same given rpm that you had with a stock camshaft. If you are having a problem with the air/fuel mixture screws not making a difference then what happens is with turning the curb idle screw in farther this will sometimes cause the throttle plates to open too far and they will uncover the idle slots. This will allow it to bypass the idle circuit and start pulling fuel from the transfer slot. To correct this problem you can raise the secondary throttle plates a little with the secondary adjusting screw allowing more airflow into the engine. This will allow you to lower the primary throttle plates so you will be able to get back into the idle circuit. Another method would be to drill a 1/64" - 1/8" hole in each of the primary throttle plates on the side closest to the transfer slot. This will allow extra airflow into the carburetor also alowing you lower the primary throttle plates.

And Another Article on the power enrichment system
(Power Valve(

http://www.holley.com/HiOctn/TechServ/TechInfo/TI-222A.html