Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Fuel dripping out of primary's
maddogs1965:
Hey Cliff!!!
So i will try and keep this as short as possible with supplying the most info for you.. :)
So i have my Fathers 69 GMC truck S.W.B. fleet side 2 wheel drive with the #'s matching original 396 from the factory in it. I have just recently had the motor re-built since it had over a 100,000 miles on it, and since this truck is so rare, i am trying to keep it looking as ORIGINAL as possible, so i am trying to keep the Q jet.
Motor specs after re-build.
The motor has been bored .30 over with 9:1 compression. I had the machine shop do some head work to the original cast iron heads and and they install a set of 2.17 intake valves and 1.88 exhaust valves. I am running a Edelbrock Performer Z-0 intake manifold. I also installed a Comp Cam part # 11-242-3 which has a .515 intake lift, .520 exhaust lift with 268 intake & 280 exhaust duration.
According to my vacuum gauge i am pulling between 8 to 9.5 pounds of vacuum @ idle.
So my issues is with the Q jet is that if i turn the idle adjustment screw in past 800 R.P.M.'s in park, i start to see fuel dripping out of the primary's into the intake manifold. I am assuming since my vacuum is so low i am having issues keeping the needles sucked down into the jets, and i am going past the idle circuit into the primary circuit. I am hopping if i order your Power Piston Spring kit this will address this issue, and you might be able to tell me what color spring i need to start with. The Carb # is a 17058213
I will also be ordering a new float and your Q jet manual...
maddogs1965:
So i have been reading some of the threads on your AWESOME forum, and from what i see, it is looking like the older Q Jet carbs are the ones to have.
So besides the 17058213 that i am working on now, i also have a 17057213AWP that i rebuilt for my Father over 20 years ago and he stuck that on the truck, and i also have which i believe is the original Q jet for the 396 that i found on his shelf in his garage which is a 7029214LF.
Out of these 3 complete carbs, which one would you recommend to run on the 396?
I have already purchased a installed a rebuild kit, and ordered a float and the Power Spring kit from your shop for the 17058213, but if i have a much superior carb in one of the other two, i will start all over again with the one you recommend.
And bye the way, if i have not said so before, THIS IS ONE AWESOME FORUM YOU HAVE HERE.... :) i thought i new allot about these old carbs until i found your awesome Webb site
Cliff Ruggles:
Making under 10" vacuum is a result of the cam choice, the tight LSA and XE lobe profiles are just not well suited to a truck engine. It would have helped to use a cam more suited to a truck engine and lower 9 to 1 compression ratio.
All of the carbs mentioned would still work fine for what you are doing, my first choice would be the original truck carburetor as it is more generous for fuel delivery than later emission carbs mentioned. It will still need some idle system modifications to be happy with that low vacuum at idle and low speeds.
I would install one of our kits in it, and modify the idle system accordingly. The carb will need the orange PP spring from our kit as well, stock jets and metering rods should be fine......Cliff
77cruiser:
How do you have your timing set up? Probably need more initial timing.
maddogs1965:
--- Quote from: Cliff Ruggles on December 22, 2014, 05:17:54 AM ---Making under 10" vacuum is a result of the cam choice, the tight LSA and XE lobe profiles are just not well suited to a truck engine. It would have helped to use a cam more suited to a truck engine and lower 9 to 1 compression ratio.
All of the carbs mentioned would still work fine for what you are doing, my first choice would be the original truck carburetor as it is more generous for fuel delivery than later emission carbs mentioned. It will still need some idle system modifications to be happy with that low vacuum at idle and low speeds.
I would install one of our kits in it, and modify the idle system accordingly. The carb will need the orange PP spring from our kit as well, stock jets and metering rods should be fine......Cliff
--- End quote ---
Hey Cliff!!!
Thanks for getting back to me.
As far as the cam choice, i have a friend with a 57 Nomad with a 468 in it, and i really liked the performance of his cam and engine, so that is why i chose the cam i did to match his and had the intake and exhaust valves re-worked. Basically i was trying duplicate his motor as much as possible minus the bore and stroke.
Thanks for the heads up on the orange PP spring, and i am looking forward to receiving you manual so i can mod my Idle Circuit accordingly. I will stick with the 17058123 carb for now, but if i do like the final results, i will start over with the original carb.
--- Quote from: 77cruiser on December 22, 2014, 06:12:15 AM ---How do you have your timing set up? Probably need more initial timing.
--- End quote ---
Hey Jim
It has been a couple of months since i timed the motor, but if i remember correct my initial timing is at 23* and total is at 32*. Of course it does not help one bit that i live in Truckee CA. at a elevation of 6500, not much oxygen up here :'(
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