Was just trying to get the car dialed in a little better by using a vacuum gauge and the highest steady vacuum reading I can get is 13.5 inches at 800 RPMs.

I played around with idle mixture screws and curb idle screws and secondary idle screws and none of it made much, if any difference. Timing is at 17 degrees.

Im going to, on my next day off, do a compression test and the old carb cleaner misting test, but is there anything else I should be wary of?

It's got a 218/224 @ .050 comp xe262 cam in it, I'm thinking this thing should be idling at around 16-18 inches of vacuum. No way 13.5 is normal... am I right in thinking that? Or am I barking up the wrong tree by trying to "fix" something? Intake gaskets?



The needle (As you can see) is steady, it jumps around a little with the cam lope (which is very mild) but it's more than stable enough for a clear picture from a phone, so it's not oscillating at a high frequency or jumping way up and way down or anything. It's pretty stable... just lower than I figured it should be.

 

Check for gauge accuracy, I had one that was off by 1.5''.
Is the gauge hoked to a good manifold source? Ilike to hook up at the brake booster fitting.
Timing seems low, it that reading w/ vacuum advance?

 

probably about right for that cam.

 

Comp says that manifold vacuum tested at 17.5" Hg @ 800 RPM & 18.5" Hg @ 1000 RPM w/ no load on their dyno.
A compression test is never a bad idea. It can provide some real insights into how well your engine has been spec'd and it's current state of health.
How old is your carb? That's something to consider as well as the usual examination of the vacuum lines and fittings.
I haven't tried the "old carb cleaner misting test" however I have tried using propane with mixed results.

That's something to check into as well. I've had the same experience.

 

does gauges are not acurate at all, a little bump and they get out of wack, i have one, make sure it's zeroed out. 13" is the best i get with my cam (275deh) in drive

 

No vacuum advance, all mechanical for these purposes.

I hooked it up to the line going to the brake booster. Is there any way to check the gauge's accuracy beyond just buying another gauge?

1. Carb is 4 or 5 years old. 3 years ago I bought a billet baseplate for it thinking there were vacuum leaks in the throttle shafts of the carb but it made no change and I found out what it was later on (was a linkage issue). But the baseplate is new, and the old one performed no different anyway.

2. My vacuum system is literally just PCV valve and brake booster. That's it. Simple to troubleshoot in that regard.

3. Im guessing the best way to check the accuracy of those things is to buy another? I never treated it that gently so it's possible. I used it to try to find an issue on a friends 4.0 Jeep the other day, and it was only pulling about 15 inches of vacuum through this gauge. It's running EXTREMELY rich despite all the sensors reporting normal ranges, so Im not sure if perhaps the gauge is just 2-3 inches low, or maybe the jeep AND my car are both pulling very low vacuum numbers, but it definitely adds to the idea that perhaps the gauge is wrong.

4. I use that weird plastic/rubber gasket for my vortec head intake gaskets, I remember people had issues with leaks with them, mostly coolant leaks. Was suspecting there was a vacuum leak in the valley. Seems like kidn of a long shot, though.

 

Fwiw, by comparison my 355 + xe262 gets 18" at 800 rpm in park, base timing 15 deg. I'd grab another gauge just to compare.

 

I've checked vacuum gauges by using a vacuum pump, thy should be the same reading.

 

As an experiemnt, try your vacuum test with the PCV line and brake booster disconnected and plugged.
A crankcase valve stuck slightly open, or one that's not matched to vacuum characteristics of the engine may represent a small and steady vacuum leak. The same can said of the brake booster. It's not unheard of for the booster to develop a leak. It's not common but it has happened.
Quick question: Why no vacuum advance?

 

How was the cam installed? Did it go in straight up, or retarded? Did you degree it at all? Usually, Comp gets the pinning pretty darned close, but there can be a lot of variance in timing sets.