Q-jet

[TexasRed]

Ok, I just got a q-jet built by a performance rebuilder to replace an edelbrock performer. My question is I need to get a good baseline because this carb is being weird. Around idle, if I put my hands over the primary (without trying to close the choke in the process), it takes about five seconds and then it wants to start to die. If I remove my hands, instead of picking back up, it continues to want to die, unless I close the choke by hand, which the engine picks back up, sometimes at a faster speed than before I tried the hand trick. So maybe I have a vacuum leak somewhere? I sprayed ether around the base of the carb and it didn't seem to significantly change the rpm of the engine.

I have an 84 with a 305 so there's a crapload of vacuum hoses, I don't have the EGR hooked up currently (for tuning purposes I swear!). Is there a vacuum diagram that's much simpler so I can disconnect the crap I don't need while I'm tuning? The gas in the tank has been there for a while so I'm trying to burn through that a little bit. Can I just hook up the vacuum canister of the distributor, PCV, and I'm not sure what else needs connecting? I have a charcoal cannister, but I am not sure what needs to be connected/disconnected. This way if it still acts like I have a vacuum leak, it may be the intake manifold somewhere I can't get ether to. According to the vacuum diagram I'm supposed to have somesort of "Delay" for the distributor (and I think maybe for the EGR too). . . .what is that? I'm sure I'll have some questions about simplifying this mess GM thought would be good (I guess it was good for the estimated life).

Thanks for any help!

[Blue 82]

Autozone has the vacuum diagrams

[Blue 82]

[Blue 82]

There's a ton of diagrams here
http://www.autozone.com/servlet/UiBroker?ForwardPage=az/cds/en_us/0900823d/80/11/4c/4a/0900823d80114c4a.jsp

[VileZambonie]

EGR does no good while the engine is cold. For lowering HC and CO emissions the Vacuum advance was also disabled at start up. They were either controlled by a vacuum solenoid or (TVSV) Thermostatic vacuum switching valve. They also worked on ported vacuum which only recieves a vacuum signal when the throttle is opened.

Here is what I would do. Make sure all your vacuum lines are hooked up correctly... Brake booster, PCV, canister etc. I would run full vacuum to the distributor not ported. Adjust the timing, then set your choke, fast idle, and your idle mixture screws. If it's still acting up and you have everything set correctly with no vacuum leaks, bring him back the carb

[TexasRed]

Thanks Blue82, but I was trying to go simple,  I have the vacuum diagram on truck still, but some of that stuff is in a little disrepair after over 20 years of service.

How do I determine the right amount of fast idle? I think choke is right. The carb should be good since he's well known in Houston and he sets it up on a test engine (albeit a circle track setup). Well not sets it up, runs it on there. The mixture screws Im gonna need a new dang tool . Either a trip to Harbo(u)r Freight or the local auto parts store. I'll put the gauge on it too. Does the lightly seat the mixture screws and then 2 times back out still apply before setting it?

Also, nothing is connected to the switch connected to the switch in the thermostat housing. A mechanic that was using at the time decided to unhook a bunch of stuff and hooked it back up differently (everything ran), so I'm almost blind here.

Thanks again guys, I'll try to take a look at it tomorrow.

[VileZambonie]

post a few pix of your engine.

[TexasRed]

OK here goes. I think maybe the brake booster could be leaking some vacuum. I know when I touch it with the engine off, you can hear it hiss some, not today. I included a photo, maybe I need to bend a hard line as it looks like it comes into the booster from the carb at perhaps a too odd of an angle. Also, when the engine was running and I was in the cab I could hear a kind of hiss, maybe that was vacuum lost at the brake booster? It didn't backfire so it couldn't have been ALL the vacuum being lost. LOL. Also when I revved it up in park, the rpms would hang after letting the throttle down, maybe it's lean because of a vacuum leak?

http://s57.photobucket.com/albums/g207/hippiegohome/?action=view&current=carb.jpg

http://s57.photobucket.com/albums/g207/hippiegohome/?action=view&current=booster.jpg

http://s57.photobucket.com/albums/g207/hippiegohome/?action=view&current=another.jpg

This switch below broke when I was trying to put the PCV line to the carb. Nothing was connected to it and it's the one that goes into the Thermostat Housing. Not sure why I capitalised that.

http://s57.photobucket.com/albums/g207/hippiegohome/?action=view&current=brokenswitch.jpg

This is a switch that goes into the manifold.

http://s57.photobucket.com/albums/g207/hippiegohome/?action=view&current=udderswitch.jpg

This I think is the vacuum delay switch for the egr and distributor, but the vacuum lines on it have deteriorated.

http://s57.photobucket.com/albums/g207/hippiegohome/?action=view&current=WTH.jpg

If you need more pictures, let me know. Thanks!

[VileZambonie]

use the image code when you post pix so we don't have to click on the links...

it looks like this ... [ img ] link in here [ / img ] no spaces of course....

Now if you think the booster is bad just block off the vacuum hose and see what it does. It also looks like you have a 3/8 hose just laying there in the 1st pic. What does that go to?

[TexasRed]

Well, the pictures a little big so I usually link to them because it helps people on dialup.

The 3/8ths hose goes to the air cleaner.

I'll try blocking off the vacuum hose to the brake booster. If it turns out to be bad, does that mean I have to replace the whole thing? Just curious.

[VileZambonie]

yah the booster is a sealed unit.

what's dial up? lol

[HAULIN IT]

Tex, The hose that you said "It Goes to the air cleaner", Is it the hose coming out from the front of the carb? What exactly does it hook onto at the air cleaner? Did you have it plugged while running the engine?

[TexasRed]

HAULIN IT, nah, it's the hose that's sitting there that I believe goes to the decel valve I think, When I'm running the engine I just leave it alone.

I think maybe my cruise control may be leaking vacuum, that's why I hear a hiss in the cab, But I'm going to plug off some stuff later. To run properly, all I need is vacuum advance, pcv, air pump, egr, and a few other things.