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So there's this thing on the back of my intake...

handloader90

handloader90

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The intake is an Edelbrock Performer RPM sitting on top of a 350. I did an engine swap back in January in a hurry and left the intake the way it was and threw it on the newer engine to get things running.

Ok, so I have this thing on the back of my intake literally right behind my carb and nothing has ever been hooked up to it. I assume that it's a vacuum fitting, it's got two openings, one is broken off and the other one I just put a cap on (I took the cap off for the photos).

Now my engine makes this sucking/ hissing noise, more of a sucking noise. It gets louder the more I push on the pedal and it doesn't really bother me, but I'd rather it not make the noise.

My engine temp is fine, don't seem to have problems with power or anything weird going on and my engine seems to be functioning normally like it always has, but this thing is starting to irritate me.

I want to unscrew it and put a plug in it, but I figured I'd ask on here and see if that thing is important and if I need to get another one and route any vacuum lines to it instead of plugging it.

Also, if anyone knows the thread pitch for the hole that it's in please let me know, it'll save me a call to Edelbrock.

Here's the photos of it and it's location, I put a red circle around it in the photos.

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The trucks a '76, so at some point the tranny was swapped to a 700. It's a 1/2 ton so I'm gonna guess a 350 turbo was there and whoever owned it at the time left the vac fitting on there. If that's the case I should be fine to plug it then, huh?
 
That's what I'm planning on doing. Do you think that's where my "sucking" sound is coming from?
 
ryoken said:
surprised it holds an idle...
Click to expand...

Right? It actually doesn't idle too bad (or it didn't), it's currently timed by ear due to a slightly loose dizzy clamp that allowed my dizzy to rotate when I bumped into it about a week and a half ago and it's still off a little, idles at about 1000 RPM, I had to bump it up that high with the idle screw just to keep the engine running, if I didn't do it that way the engine would instantly run at around 300 RPM while in gear and begin to stumble when the vehicle was stopped (had to keep one foot on the brake and give it a little gas with the other at stop lights to keep her running). So now I get to do everything right... correctly time the engine, rejet and tune the carb for a major altitude change and deal with my sucking intake hole.

I plan on replacing the current fitting with another fitting with only one outlet so I can get my vac gauge hooked up when doing my carb tune.
 
This turd is my daily driver. As much as I hate to run it this way it's what I've got to until I get my calibration kit, vac gauge, timing light and the new vac fitting.

The good news is that the trucks on a car carrier and I get to drive the grocery getter Trailblazer for the next few weeks. The truck won't be ran for another 3 weeks and as soon as myself and the truck meet up in Kentucky I'll be in the hotel parking lot tuning it up!
 
the vac leak and proper timing should be your absolute priorities... rejetting for altitude isn't nearly as important...
 
As was said that is a full intake vacuum spot. I've seen brake boosters hooked in that location as well. I bet the one on the back of the carb has the same size fitting. You can cap it or put a single barb fitting on there for testing, and I'm betting the engine runs a ton better as its running Lean right now with the extra air sucking in through that fitting. Just make sure to Put a nipple back on it when you get it running right again. 14.2 is I believe optimum vacuum so try to get as close to that as possible. I've heard most carbed engines won't get about 10-12 psi vaccum though. I've never used the vaccum gauge method yet.
 
chulisohombre said:
As was said that is a full intake vacuum spot. I've seen brake boosters hooked in that location as well. I bet the one on the back of the carb has the same size fitting. You can cap it or put a single barb fitting on there for testing, and I'm betting the engine runs a ton better as its running Lean right now with the extra air sucking in through that fitting. Just make sure to Put a nipple back on it when you get it running right again. 14.2 is I believe optimum vacuum so try to get as close to that as possible. I've heard most carbed engines won't get about 10-12 psi vaccum though. I've never used the vaccum gauge method yet.
Click to expand...

Thanks you for the awesome info! My next question was going to be can I put a "T" fitting in there and hook my brake booster up to it (instead of using the port on the back of my carb) and then cap the other port on the "T" fitting and just hook up a Vac Gauge from time to time when needed.

Would a setup like that affect or take away from my braking power?
 
I just wanted to say thanks to everyone who took the time to look at this thread and give me some great info and advice, everyone's feedback is greatly appreciated!
 
Quick question.

Does anyone know what pipe thread that port is? I called Edelbrock two separate times today and was told two different things. The first time I was told 1/4" and the second time I was told 3/8".

Just curious if anyone can confirm either one of these numbers.

I'm going to call again and see what the next rep says.
 
Another question.

Does anyone know what the inner diameter size is of the hose that comes from the brake booster which I will be attaching to this new fitting I'm going to buy. The truck is a '76, I threw that in there because I don't know if the hose size changed in later models.

Wish my truck was still here so I could just get all the measurements myself...

Also, what would you guys say the most common size for a Vac Gauge hose would be?
 
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