I dunno couple issues

[Yupiamlo]

Alright here you go, go crazy lol

[Corts60]

So the EGR and Vacuum advance are hooked to the same connection. Now is that connection manifold (full time) vacuum or ported (off idle) vacuum?

[78 Chevyrado]

Check the other end of the vacuum line to the transmission, its the metal line right in front of the dist. I had the one on mine rot and come off and i didn't find it for a few days and it ran like crap.

[Yupiamlo]

I think its full time because when I unplug the vacuum advance it revs up, so its gotta be sucking more air, is their any problem with running them off the same thing? and thanks 78 but I already checked that one haha.

-Adam

[timjt]

Hey, I didn't read the last few but I have had an 82 and 85 with these same issues. Like the guys are saying, check for vacume leaks! my 82 with a bunch of random preformance parts had a edelbrock carb and it had two or three major unplugged holes which killed the truck almost every time. The timing was off too, just replacing a cracked distributor cap made vast improvements. You know how to make sure your wires are in the right firing order right? mine were mixed all up when I checked 'em and that alone will cause the engine to barely run. When you adjust the idle jets its a significant difference when I did it....

[Corts60]

Well, if when you unplug the vacuum line and it revs up, it sounds to me like the engine is starving for air. Have you checked to make sure the choke is not sticking?

Also, if you are going to re-set your AFR, use a vacuum gauge if you have one and you want to set them for best vacuum reading.

-Cort

[Yupiamlo]

Thanks timjt, I did a Cap, Rotor, checked for spark, and the firing order, all is good there. Timing for the distributor is a lil ballparked but its set where its running best, so yeah im thinking maybe another small vacuum leak.

The chokes definatley not sticking, i have it set to be stuck open right now so that it cant interfere, and yeah that sounds good for the AFR screws with the gauge, but currently its not making a difference how I have them set.

[dammitmitchell]

then you definatley still have a vaccum leak.

[tucsonjwt]

I think you should get the shop manual instructions/graphics for routing the vacuum hoses. I can see right away that you have at least one (probably two) ported vacuum switches (aka TVS - thermal vacuum switches) at the water outlet (where the upper radiator hose connects to the intake manifold). You also have a plugged off vacuum fitting at the front of the carb. Many people disconnect the vacuum hoses to simplify things, but I think it just makes things worse. Here a pic of my 83 C20 big block, showing one TVS at the water outlet. I have a threaded plug where your other TVS is.

[lindstromjd]

What CFM Quadra jet do you have? If it came off a corvette, I'd say it was an 800 CFM. I have an 800 on my corvette, and the thing runs like total crap unless you turn the mixture screws out at LEAST 2.5 turns. I think that's your main problem; the bigger q-jets like to have more fuel going to them, especially since you said it was re-manned. I'll bet someone turned it up a little when they rebuilt it. Turn your screws out more and see what happens. I run mine at 25mm out.

[Yupiamlo]

Damnmitchell, yeah Im gonna play tomorrow night sor saturday, I had to shim the starter the other day and it dropped and hit a cooler line, and arced and put a hole in it, so I fixed that today, and back to the original problem, this stuff gets annoying after awhile lol.

Tuscon Ok I can run that vacuum line but what does that do, and how will it make the driveability improve? Is it hurting anything by not being plugged in now?

Lindstromjd I dunno what CFM quadrajet it is its an M4MED it was what was stock on my truck with the 305, and I got a replacement one. But quadrajets, at least as far as the secondaries go, they will only suck what they can use like from what I understand their not like an edlebrock or holley cfm rating, their what your engine wants... maybe?

-Adam

[lindstromjd]

The quadra-jets are pretty fuel efficient, yes, but I know mine isn't quite like the rest of the carbs I've dealt with. An Edelbrock 650 would run fine with the mixture screws 1.5 turns out, but my q-jet just doesn't. Try turning them out another full turn and see what happens. It will raise your idle, so you'll probably have to drop the idle screw a little, but I would be willing to bet almost anything that that's your problem; not enough fuel going through the jets into the intake.

[tucsonjwt]

It looks like you have two "ported vacuum switches" or "thermal vacuum switches" which need to be hooked up. I don't know where the hoses from your switches go - maybe another poster can show the connections for your year/model/engine etc. - can you post that here? This is why you need a shop manual to show where the hoses go. You can get vacuum hose routing from online services, like All Data, but I no longer have a subscription. These hoses may or may not affect your engine performance, depending on what is going on at the other end of the hoses that are supposed to be there (capped off? rerouted?,etc.)
In my case, when I got my truck 8 years ago all of these vacuum hoses were disconnected and long gone. I replaced the TVS and got information on where the hoses went, then the engine seemed to run a little better - mostly at idle, which allowed me to lean out the carburetor and save a little gas.
As far as what the TVS could do, here is a listing of possible purposes, but it may or may not pertain to your truck. Good Luck.
P.S. I think vacuum controlled devices on a vehicle are the worst idea ever, which is why more and more of them are being replaced by electrical devices on new vehicles.
http://en.wikipedia.org/wiki/Vacuum_switch

[dammitmitchell]

and the end of all of this you'll be a master at fixing this.
it takes time. e all go through it. good luck!

[379redneck]

my 87 did the same thing. It run fine for a few minutes and then shut off like some turned the truck off. It would fire right up and shut off sooner unless I stayed on the gas. It ended up bein the control module.