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Quadrajet vacum mess

79k20350

79k20350

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So basicly I just need to know what i need to leave for correct operation... vacum secondaries? Also which vacum port is ported for the dizzy.

Final thing is switching it over to a manual choke. Only carb ive run beofre was an edelbrock, and there was alot less to it:crazy:
 
Seems like the more reading i do the more confused im getting:doah: Ill go take pics and see if that helps:crazy: btw this is a 79, and has hot air choke
 
here are the pics. Id like to go to a manual choke if thats at all possible...

q jet 1.jpg

q jet 2.jpg

q jet 3.jpg

q jet 4.jpg
 
I have been trying to get up to speed on Quads, so here it goes. Lets trade help since yours is fairly stock. The front "can" overides the choke when the throttle plates are opened, increased signal pulls choke plate off to all more air. When signal goes down, choke returns to wherever the bimetal is. Rear "can locks the secondary air valve until the choke is off

I am searching for a manual conv. kit, will edit when I find it.

I assume you could eliminate fast idle, I think it would engage with A/C. The factory idle screw would then need to be adjusted, assuming you have one. Sorry for my ignorance on this part, but my expeditions to the P&P to learn more on carbs is unfruitful because most are gone.

More info to come after I go play and read through Doug Roes book.

Now, how you can help me. How is the rear "can" plumbed in?
***Edit***, CRAP, your rear "can aint plumbed in either. I assume however, that it goes through a temp. actuated vac. switch.
 
Last edited:
Kenny78 said:
I have been trying to get up to speed on Quads, so here it goes. Lets trade help since yours is fairly stock. The front "can" overides the choke when the throttle plates are opened, increased signal pulls choke plate off to all more air. When signal goes down, choke returns to wherever the bimetal is. Rear "can locks the secondary air valve until the choke is off

I am searching for a manual conv. kit, will edit when I find it.

I assume you could eliminate fast idle, I think it would engage with A/C. The factory idle screw would then need to be adjusted, assuming you have one. Sorry for my ignorance on this part, but my expeditions to the P&P to learn more on carbs is unfruitful because most are gone.

More info to come after I go play and read through Doug Roes book.

Now, how you can help me. How is the rear "can" plumbed in?
***Edit***, CRAP, your rear "can aint plumbed in either. I assume however, that it goes through a temp. actuated vac. switch.
Click to expand...

Thats how I hooked it up. I think i got it good enough:o
 
I don't post up much, but maybe these can help...

These pictures were taken not long after I got the Blazer, so it should be the factory set up (don't mind the dry rotted vacuum lines, most have been replaced)

Pictures are of an 1984 305 Blazer

P1010822.JPG

P1010824.JPG

P1010826.JPG

P1010828.JPG

P1010829.JPG
 
NotLaw, those pictures are exactly what I was looking for. Around here emissions are nonexistant and unmolested engine bays are rare, making putting a quadrajet back on a truck difficult. The vac can on back is plumbed directly to manifold vac. Which confuses me. It appears to lock out the secondary A/V's, but applying full vac. would prohibit them from opening.
On second thought, high load, low signal would unlock them and allow to open. I wish I had my carb. in front of me to look at this. But I digress...
Thanks again for the pics.
 
Hot air chokes and electrics are very interchangable on this generation. Change coil, plug vac. hole??? if going to electric and hookup
 
I just ordered a edelbrock intake and carb... problem solved:crazy:
 
saw this too late--I can get all the routing from mine for you tomorrow, and the electric choke is really easy once you get the vacuum stuff worked out. The Q-jet is a really nice carb if it's set up properly . . .
 
Sure, I was thinking it might be helpful for someone else anyway. I presume you're looking for routing to maintain all important functions and eliminate unnecessary crap? :haha:
 
Wrench said:
Sure, I was thinking it might be helpful for someone else anyway. I presume you're looking for routing to maintain all important functions and eliminate unnecessary crap? :haha:
Click to expand...
me, i have none of it, and want to know what i have to hook up :crazy::o
 
For me, I would like to expand my knowledge. In this thread i figured out the last head scratcher on mine. Everything else, except evap. fuel is laid out.
 
EVAP fitting is shown in Notlaw's photos...air horn, (top 1/3rd of carb) front, drivers side angling down at 45* or so.

What makes the later Q-jets so complicated is the switches that were being used to run multiple devices. You need almost none of it for the carb to work properly, as a matter of fact, ignoring everything else (timing, any other emissions stuff), choke pulloff and vac. secondary break are all you really need for it to work properly.

The choke pulloff is there to crack the choke plate once the engine starts. The choke blade should be completely SHUT when the throttle is tapped before the engine starts. The secondary vacuum break works as mentioned, engine load increases, vacuum decreases, break relaxes allowing secondary to open at the rate the break "loses" vacuum.
 
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