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Quadrajet question


amsterdam84

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I found out that the carb on my car was built for a "454 Stinger". Since changing over from 2 to 4 bbl, I noticed a massive increase in fuel consumption with no noticable gain in performance as well as constant backfiring. My guess is I need to put in smaller needles in the carb. I have a 350 with a quadrajet carb and I'm told it is pretty simple to change them over. Do I only need smaller needles?

 

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you're better off buying one that has been set-up just for your car, it's well worth the money

 

you'll spend forever playing with it to get it right, and prob never get it just right

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Rods and jets should be replaced as a pair.

Pretty much, the jet size controls how rich the mixture will get under load, and the rod size controls how lean it will get at cruise. The problem is that there is a relationship between them and it can be ruined if you were to install a bunch larger jet without changing the rods also.

 

I understand these Q-jets pretty well and still couldn't get mine right until I took my car into the shop and had it put on a dyno with an exhaust analyzer. I had a new carb that was supposed to be pre-tested and setup for my application, but it was messed up from the get-go and having the exhaust analyzed told the techs what needed to be done to get it right. I spent $$ on the new carb, then another $$ on having it setup...I should have just had my old carb setup and I could have saved the purchase price of the new one.

 

As stated above, I'd start with the stock rod & jet combo for a factory 350 and that should get the fuel ratio where the engine wants it. That should bring it alive!

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At the same time as replacing the carb, I added an Edlebrock Performer intake, headers and it already had a mild cam. So I wasn't worried about it being too big.

 

I only realized after reading some old emails that the original owner told me what it was built for. So my guess is its got needles and jets too big. I picked the Qjet because I wasnted SOME fuel economy because of the small primaries. I also have heard how hard it is to diagnose these carbs. Not many people in my area know much about them so I might have to go a bit farther out.

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I just hate the thought that I've spent so much money already on it. I almost got it dirt cheap on Ebay and at the last second someone upped the bid from $45 CAD to $92. Plus shipping and plus an additional $100 to have it rebuilt. I could have bought a brand new carb for the same amount.

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To make matters worse, there are two kinds of Q-jet and they use different rods that don't interchange. The old style Q-jet is what our cars came with and they use a shorter rod. These parts are harder to find. The late-model Q-jet has a part number starting with a "1" and uses longer rods. The difference isn't significant and unless you see them side-by-side, you wouldn't know whether it was long or short. I'd guess the difference in length might be 1/8 of an inch? The good news is that the jets are all the same. I'm not sure if Edelbrock still carries the Q-jet parts...when they did, they didn't have the short rods at all.

 

My 468 is happy with a late-model Q-jet with 72 jets and 37 rods. Since the rod/jet combination controls the mixture and not the quantity, this combination should provide the right air/fuel for any engine I choose to bolt the carburetor onto. I'd say that this would be a good starting point for yours also.

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ok, first off.. if it's a 454 carb, you need SMALLER jets, and BIGGER rods.

 

it's way to rich.. I started out the same with my qjet.. it came off a buick 455 and would actully stall if I got into the secondaries cuz it was dumping so much fuel in smile

 

they have the right suggestions, you should find the 'stock' rods/jets for a 350 and start there. the jets and rods dont' go "as a set" but they are changed together, or seperately depending on what u are trying to change.

 

if you want to affect only the part throttle cruizing mode, then change only the rods.

 

if you want to change only the WOT power mode, then both rods and jets are necessary.

 

Jet size minus rod size = cruise settting

Jet Size minus "26" = power setting.

 

the numbers created here are basicly just 'relative' numbers as a guide to figure out where you need to go.. the "26" comes from the fact that ALL primary rods for qjets have .026 tips

 

you can interchange the long and short rods, provided you know which ones you have. you can simply bend the arms of the rod hanger to compensate for the difference.

 

tomorrow I'll dig my qJET stuff out and measure the two rod sizes and tell u which are which if u want.

 

 

btw. u should see a small improvement in milage going to the qjet. over the 2bbl. .the qjet's primaries are much smaller which lead to better throttle response and milage, assuming it's tuned correctly :>

 

fi you don't want to get into the hassles of tuning a qjet.. check out a holley street avenger.. they're nice carbs.. not as nice as a qjet.. but easier to work on :>

 

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Thanks for the tips, looks like I have some research to do. I can probably bump the sizes up and down a couple numbers due to the mild cam and headers. I'll see if I can find some kits around here somewhere.

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  • 2 months later...

ok, its time to dredge up an old topic but I need to know what the original sizes for jets and rods. I can't seem to find what sizes the originals.

 

I found a site that will sell a kit with springs and rod/jet pairs and will include 3 sets of each but I need sizes to order.

Thanks for the help guys.

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I'm not sure what a real original Q-jet came with.

Edelbrock used to sell "factory replacement" Q-jets that were supposed to be ready to bolt on and pass emissions requirements, so they would have to be pretty close to ideal. They don't sell these carbs anymore, but their web page is still up and they give rod & jet sizes! It looks as if most of the early carbs came with a 69 jet and 36 rod.

Maybe this page will help: http://www.carburetion.com/Rochester.asp

 

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