General Category > Quadrajet Carb Talk and Tips
Float level and other Qs
Frank400:
Jet and metering rod sizes BY THEMSELVES don't mean a thing as far as rich/lean is concerned. It's the COMBO of jet/rod AND air bleed size that matters. It's all explained in Cliff's book which is a must read for any attempt on using a Qjet outside it's original application. Once you'll read it ALL, then you will see the light.
Frank.
Cliff Ruggles:
Correct. That article is really only useful to determine metering area as it doesn't take into account other items with the carb that effect fuel delivery across the load/speed range.
It is not possible to compare what it used in one carb vs another for jets/metering rods and there are a dozen other items that effect end fuel delivery to the engine.
For example, a 1969 Chevy carb part number 7029207 will delivery more fuel to the engine using .065" main jets and 36B primary rods than a 1970 7040205 using .077" main jets and 49B metering rods.
This is because the 1970 model uses HUGE main airbleeds vs tiny MAB's in the 1969 unit.
Idle fuel is also a significant player in fuel delivery and not really factored into the literature you have been looking at. The idle system feeds fuel down to the mixture screws and transfer slots. Some transfer slot is exposed at idle and as the throttle angle increases more slot is exposed and fuel delivery increases supplementing the main system in the "normal" driving range.
When we supply rebuild and tuning kits here I look at the carburetor number being used, how it is set up by the factory, then put the correct parts in the kit for the application. Very few if any other folks in this industry can do that for you, and I can recommend how to set the idle system up as well for any carburetor part number used on any engine combo.......Cliff
Macadoo:
Thanks for the input and explanations, fellas. I've been through the book a few times now and, at this point, my notes, highlights, and comments make it hard to read, lol.
I discovered that the first Q-jet I modified ('81 APT), using Cliff's book, was pretty warped. It accelerated very well but still wouldn't idle. I had another laying around (a 1705 era) so I was having a go at that one when I, and this is hard to admit, accidentally drilled through one of the main fuel nozzles while cleaning up a burr. :-[ I have yet another '81 APT but it is more warped than the first. This seemed more than coincidental so I checked the intake's mating surface. Yup, it was rounded over (the only part I bought for the new 455 that was used). I've got it flattened and am back working on the first '81 APT carb. I know there are un-warping services but I thought I'd give it a go. It's pretty darn close now. I can't feel any rock of the air horn with a single gasket in place but I might use two gaskets for good measure. Or will that interfere with the power piston/ rod hanger?
Anyway, I'm just doing all this to learn and have fun. I'm hoping the Q-jet I'm finishing up now runs because I'm not a big fan of the Holley I have on there now. It's my first Holley (a gift from a friend) but I'm not very impressed. But to be fair, I haven't tuned it. It's "out of the box" stock.
Cliff Ruggles:
We spent some time last year with a brand new out of the box Holley Street Avenger.
It was installed on a good friend of mines new SBC engine for his work truck. I had NOTHING to do with the engine build or anything used on it. A local Chevy "guru" did all the work and picked all the parts.
It was a 400 SBC with early double hump heads on it and unknown Comp XE camshaft. From day one it didn't run for chit anyplace, HORRIBLE fuel economy and quickly developed a history for being very unreliable.
He uses the 1 ton Chevy dump truck for his tree service and pulls a chipper with it, and hauls heavy loads, etc.
Fuel economy with the new engine topped with the Edelbrock intake and Holley carb is gallons per mile instead of miles per gallon! Takes about 20 dollars worth of fuel for a local 10 mile round trip to and from a job site. A trip to Columbus 50 miles away is over $120 worth of fuel.
The previous stock 350 2bbl engine was about 3 times better.
Anyhow, from day one the POS electric choke on the Street Avenger did not work correctly no matter where you set it. So it ended up getting wired open. He's been left walking a dozen times and I've grabbed a BFH and screwdriver to rescue him when he breaks down close to here at least half a dozen times. The original engine builder/guru finally kicked my friend to the curb and we had the truck brought here with a roll-back last time it left him walking.
I had a 1973 Olds motorhome Q-jet that was never claimed in the back room, installed it with no modifications anyplace other than an electric choke and it is FLAWLESS! Fuel economy is back where it should be, and it has been dead solid reliable now for many months.
I had the fuel bowls off that Holley half a dozen times and replaced the N/S assemblies several times as well. I did notice that this new fuel was de-laminating the shiny material it is made of, but it also has fundamental issues that go WAY past that problem. By far and above it's the biggest POS I've worked on in many years and I would avoid them at all costs......FWIW......Cliff
Macadoo:
Vindication is worth A LOT! I'm tired of my gear-head buddies asking me why I'm building a Quadrajunk for my new motor. It may take me a few tries but once I get it, they'll see why ;D
Is there a good place to shop for non-warped Q-jet cores. I even checked my original 1971 carb. This was a one owner car and the only time I messed with the carb was to remove it and it, too, is warped. Pretty badly warped.
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