I'm sitting right around 3000ft above sea level. High desert in central oregon. Cam is

 

Edelbrocks they tell you to use a 7/64 drill bit to measure the float height, you tip the upper assembly of the carb upside down (while its removed) to have the floats drop toward the top of the carb upper plate. Then you put a 7/64 drillbit in between the float and the upper plate. The float should just touch the drill bit. If its too low or too high, you bend the float's attachment brass arm until it is correct. You literally grab the float and bend the arm. Then flip the assembly back over and install it back on to the carb.

 

If you're at 3000 feet that will drop the average manifold vacuum about 3", so maybe 17" would be typical for a stock engine there.

A "mild" cam, not too sure about what that might do, but it should be close if it's not too radical. Has to do with valve overlap. Perfomance camshafts are tuned for high RPM. This is why the really radical camshafts aren't very good for a street driver, they don't run smooth till north of say 5,000 RPM, they won't idle well, etc. Who installed the cam? Was it degreed in to be sure where it's at?

Another factor, is where the cam is installed. An aftermarket cam is usually installed "straight up" but may have several degrees advance ground into it. Valve timing is different than ignition timing, but it also affects average manifold vacuum. Even a stock camshaft can be advanced and will improve low end grunt, useful for trucks, rock crawling, and higher altitude. A big part of tuning is just measuring and knowing for certain where all this stuff is. Compression, timing curve, manifold vacuum, and proper carb baseline setup and tuning, jetting etc. After a while it'll even seem like ya know what yer doin'!

 

3000 miles on engine, did it just start doing this? what was the last thing you did to the engine before it started acting up? Did the problems start after the truck sat for a extended period (months)?

Could be as simple as the float being stuck.

 

It's been from the beginning..first it was an hei distributor. But I swapped that holley for an edelbrock before I figured out it was the hei. I've had it in the shop, to which I was told the avs2 has tuning issues and nobody can seem to tune them. Blah blah. Anyway. So tonight I put vac guage on it, was around 20ish at idle but bouncing around like crazy. Sprayed carb clean around the engine.. .found leaks around carb. So.. buying gaskets tomorrow and putting a holley 670 double pumper on. And checking timing.

 

OK. "Bouncing around like crazy" on the vacuum gauge that's what needs 'vestigatin' for now. Look over the vacuum gauge charts carefully and try to narrow down likely possibilities. There may be more than one problem contributing to the Late Unpleasantness, but whatever is causing that needs to get fixed.

 

Sounds like you may have a vacuum leak somewhere, but it could be something else too. I'd be willing to bet the Edelbrock carb isn't your problem. Other than for troubleshooting, the Holley is best for wasting gas. A double pumper will pour gas down the carb every time you accelerate. They also leak like crazy, especially if they sit for any length of time. My favorite aftermarket carb is the Summit aluminum 600 based on the extinct Holly 4010, based on the Autolite 4100. The specs on your cam are fairly mild, but if it was made in China, quality is likely poor. It could be ground wrong. Did you also install new lifters? Did you test them to make sure the plungers work? If the lifters are acting like solid lifters instead of hydraulic, the valves my not be seating when they should, resulting in a much larger overlap than what the spec sheet calls out.

 

Engine was bought as a long block. So.. .i just dressed it and got it running..

 

Typically a rapid bouncing needle on the vacuum gauge points to a valve problem, like a broken spring or sticking valve, though could be a bad intake manifold or head gasket. Diagnostic means zeroing in on how it acts. I'm not too good at it, but the gauge doesn't lie. It's telling you where the defect is, just gotta figure it out. Find out what it ain't, and that will narrow the possibilities some.