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Carb Help Q-jet And Dist Help

Streetgliderx

Streetgliderx

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i have an 86 with factory carb and its got an electric deal infront and the truck came setup with full port distributor timing. i reset the timing and made it advance after the motor swap. was there anything else needed to be done? and i need a new carb the previous owner built the carb and bent the secondary rod that holds the butterflys... now the 4-barrels don't kick in what do you people think?
 
Hi there,

First of all i'm going to start by saying that I know everyone after me is going to post that a q-jet is crap and to get rid of it.:p: The reason most people hate them is because they can be tricky to rebuild and most people, after getting it wrong, blame it on the carb. I have a factory q-jet on my car that runs in the 12s, so if you can fix it, then are good carbs!

In fact, they are one of the best, inexpensive carbs for offroad because their good float bowl design allows them to be tipped on much steeper angles without flooding, compared to a holley or carter. The small primary bores and large secondaries also allow you to get decent milage when you want, I get about 17mpg on the highway with the 455 in my car.

Your qudrajet is an electronic unit, which started in about 1979 in some GM's. I am not sure if you replaced it what would happen, I suppose you could just get a new non-elec one and just push the wiring off to the side, but this will cause your SES light to be on and possible many other problems, someone else will probably know.

You should just be able to bend the rob back... no big deal i've done it a few times. Those rods are pretty flexible a few times. It sounds like you set the timing right, just make sure to plug the vacumm advance line back in, I always seem to forget that!:doah:

Good luck with your truck brother!
 
Slow down! :)

First off, the only way that carb is electronic is if the truck came from CA. If it has a plug on the passenger side front, top of carb, and one on the drivers side front of carb, it's a CA model, which requires an ECM to run.

If it's only got one connector, on the passenger side front top, it's not computer controlled.

Second, how do you know the secondaries don't work right? You do understand you won't get much, if any movement out of them with the truck in park/neutral, right?
 
haha, I hope I didn't sound like a now it all! I had recently drank some coffee, and I just read a whole book on q-jets yesterday so I was feeling ambitous and thats what I remembered they said about electronics. i'll just make sure to keep my newb mouth shut next time! :wink1:
 
Doesn't look like you took it the wrong way, just wanted to make sure you didn't hastily make a decision to scrap what you've got. :)

The trucks are really ignored or misunderstood when it comes to the electronic carbs, and even TBI for that matter, unfortunately a lot of material out there leads you to believe something that really isn't true, but was assumed to be fact based on what happened with the cars. Trucks really are a different animal altogether!
 
ok well its not a CA model it only has one plug.... will one form CA work can i unhook the plug part???? and i like q-jets.... when you get down on the truck pulling with it it does not sound as if the 4-barrels are opening. the truck just seems weak even after my 4.56 install
 
Gotcha! Nah I didn't take it bad at all, I just like to rant:D

Thats interesting though, it's kinda funny on how you would think something would be standard across and engine line. Did they have different standards as a far as emissions back then with truck vs car motors? I know trucks over 8500 GVW have exceptions today
 
Yes, big difference between cars and trucks. GM cars had CCC (computer carb) across the board in '81 for all the V8's, while trucks never did, EXCEPT CA trucks. You know, CA making up their own rules and all. Since the market was large enough, the manufacturers catered to CA.

I really haven't played around with those carbs. I'd have to go back and look, but I think that's a cold engine accelerator pump of some sort, meaning after the engine warms up it shouldn't make any difference. Unhook it and see what happens! :)

Can pictures be posted of the "bent" secondary rod? I've got a few Q-jets in my garage I would be more than happy to compare against.

Timing can and will make a huge difference in how the engine runs, play around with that before blaming the carb.
 
i've never been a big fan of those California rules since I work for a supplier and live in Michigan! Man, you sure seem to know your stuff!:bow:

But yah, I would double that... check the timing and from everything i've seen, read, and played around with, v8's like timing close to stock if their not a modified motor...
 
its a bone stock new gm 350 the bargain model. and the carb is together so sorry no pics but what is happening is the secondary butterflys are hanging up and hard to open with fingers only.... what is the little vacume diaphram located on the pass. side that is attached by rods to the secondary butterflys
 
That vacumm pod is an actuator that only opens the secondaries when they really need to... aka so you don't dump a full blast of fuel at 500 rpm:wink1:
 
so is it all that nessecary?... maybe its holding back my secondaries....... how can i be sure if they are not working properly
 
YES! Don't remove that vacumm pod and rod linkage or you wont be going anywhere in a hurry.

I think one of the best things you could do for yourself is to buy this book or one like it: http://www.amazon.com/Rochester-Carburetors-Doug-Roe/dp/0895863014/ref=pd_bxgy_b_img_b

They make one at auto zone for cheap too, and it will get you in tune with how things work. the last thing you want to do is start changing this or that and end up with a truck that wont even start, etc...

Heres how that all works: Lets say you put your foot to the floor at 1000 rpm. your truck in no way can take all that air/fuel flow at that rpm from 4 barrels. The vacumm in the carb holds the canister's secondary rod back, not allowing the secondaries to open yet. But as you reach higher rpm, say 2,500, and you start to lose vacumm, the canister starts to release, allowing your secondaries to open up because your motor can now efficiently use the flow 4 barrels can give.

This is why, at least from all I've read, vacuum secondary carbs are the best for street/strip use, and mechanical secondary carbs (whose secondaries open no matter what) are best for racing.

Take the hose end off of the vacuum canister, and put on a longer hose. If the suction from your mouth doesn't make the canister pull in within a second or two, it could be bad.
 
Actually putting a vacuum gauge on your engine and driving around, you'd be very surprised how little throttle equals almost no engine vacuum. As soon as you crack the throttle, that vacuum cannister is already releasing. Cruise and idle, its shut tight.
 
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