I have a pontiac 389 with an edelbrok performer manifold and 750 edelbrok carb. wondering if this is a good set up and how can I fine tune it. it boggs down when I go wide open on the throttle, it feels like there is more power to tap into if I can just tune it right.

I am not familiar with the engine but I see no reason why an upgrade to a progressive twin-choke should not improve the economy and drivability - if the right choke sizes are chosen and the carb is properly set up for the engine.

Colin Chapman proved a good performance can be obtained from a sidevalve engine by his work on the Ford E93A engine when he developed it with twin side-draught carbs for his Lotus car.

The main stumbling block will be the intake manifold that typically seems as if it was made by a plumber in his garden shed when he had nothing to do for five minutes - much of the advantage of upgrading the carb will be lost if only an adaptor is used rather than replacing the entire manifold.

A centrally mounted carb on a plumber's nightmare type manifold has inherent disadvantages that any sensible modification should try and overcome - the middle cylinders tend to run rich and the outer cylinders run progressively weaker. This is mostly due to distance from the carb and the higher percentage of fuel droplets that settle on the manifold walls and are never burned, are wasted.

The designers of such engines usually employed a hotspot design of siamesed intake/exhaust manifold to vapourise more of the fuel but this approach while slightly improving economy and mixture distribution reduces volumetric efficiency. Such engines also tend to use a small bore exhaust system that tends to increase the pumping losses of the engine.

Modifications to a sidevalve engine intended to increase volumetric efficiency and mixture control and distribution are a good idea but increasing and using any increase in performance is not, due mostly to such engines often using rather too slender and weak crankshafts and bearings to tolerate an increased performance.

Edelbrock cars are square bore and Quadrajets are spreadbore make sure you have either an adaptor plate if running stock manifold or you'll have vacuum leaks, as far as tuning Edelbrocks are EZ. 2 air/fuels screws that only effect idle, turn in till runs rough then back out 1/4 to 1/2 turn on both, that will set it for economy, for performance engines, turn out or counter clockwise till runs rough then turn back in clockwise 1/2 to full turn, set idle ***** and your good to go, the two vacuum ports in front are distributor advance, the right side closest to manifold is full time vacuum hook there for performance or left side for economy.. if you buy a new edelbrock carb it will run great right out of the box, also has a set/up DVD, for novice Mechanics, ez to change metering rods too, hope this helps, and in my opinion Quadrapuke carbs are junk.

Page 34 of this PDF manual has a trouble shooter guide - best to print 34 and 35 in order to have the side by side - several things showing to check - Check for air leaks. Make sure carburetor and manifold gaskets seal properly. All outlets must be plugged or connected. - Too lean. See Tuning Procedure. - Too rich. See Tuning Procedure - (basically, air leak, too lean, or too rich).
http://www.edelbrock.com/automotive/misc/tech-center/install/1000/1404_manual.pdf

Well, according to Pontiac Power online, a 65 or 66 Pontiac engine with XB is a 389 with a 2 barrel carb, but it was used in the B body which was the Catalina and Bonneville.
A 67 engine with XB is a 400 with a 2 barrel carb.
0489308 does not show up on the list.
Casting codes from 19064 to 1968 started with 97xxxx.

The carb you got is a 750 cfm , meant for a big block... If you have a small block in your blazer it might be too much fuel and could result in cowled plugs and poor performance after all... You should really look for a 650 cfm preferably a holly... Edelbroks are not good for off road and don't allow much room for tuning...

Remove the bolts holding it on !!

Find a vacuum "tree" (fitting with several connections that will screw right into the manifold). You can feed the distributor and the A/C dash controls from that. There should also be a fitting on the rear of the carb baseplate you can attach the power brake booster to (if needed) Make sure you cap off the vacuum port on the passenger side of the front metering block. It's "ported" vacuum and you don't really need it. Same goes for the port under the passenger right side front of the carb... block it off or connect that to the distributor instead of using the tree. I use that one for vacuum gauge attachment for tuning the carb. On a modified engine, about the only other item you may want to hook up is a pcv valve. That can be attached on a "t" to the hose for the brake but generally better to attach it directly to a fitting on the manifold. If you don't use a pcv, make sure that the valve covers are vented (I use Chrysler can type vents, commonly found on older 318's and 340"s) The remainder of the emission system can be scrapped unless you're compelled by law to keep it. On a modified system, it's pretty much useless anyhow.
I hope you also installed a good set of headers and a decent cam in there. It would be a shame to waste the potential of those heads. Only thing I don't totally agree with is the 750 carb. You'd probably do better with a 650 with vacuum secondaries. It doesn't sound as impressive but the 750 is a bit large unless you have the cam to make it work. (but probably too radical for the street)

The point gap is .019" I still have the tune up guide for this year! Does this mean I am old?

first you will need a tri power intake manifold, and then the correct carbs. its just like you were replacing a intake manifold gasket. its not a big job, but you need to know what your are doing, and then tuning them is another job, you can by tri power setups ready to bolt on from several companies.

After market cam.You sure its timed right with a degree wheel?