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 

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.

[Cliff Ruggles]

Warping isn't really a big deal provided that you have a good fit between the parts. 

I checked our books back in January and we had 12,900 work orders since going full time here in 2003.  That's how many carburetors have been thru our shop, but all were not full rebuilds, some will have been here just for bottom plug repairs, correcting issues with them, coloring/plating work, etc.

It is rare to find one that doesn't show some warping across the front due to tightening of the long bolts to the intake.  We simply make sure the fit between the parts is good.  In 99 percent of the cases where it wasn't we correct it my running the front of the airhorn across a bench mounted belt sander for a few seconds.  We then check the fit and continue this process until the top is slightly flatter than the main body. 

We also use much better gaskets that are .015" thicker and good to go.  I actually have one of the good unwarping tools and have used it a few times on carbs that were excessively warped.  It will pull the main casting back as well as flatten the airhorn.

I still don't see a little warping as a problem and it woln't be provided the builder take the steps needed to make sure the fit between the parts is good and the gasket used is effectively sealing things up.

As far as the Quadrajet having a bad reputation it is well deserved for the early models as they are pretty much HOPELESS for high performance work.  The early plunger inlet valve models (1965-66 and some early 67's) are difficult if not impossible to use for high HP applications.

Even the improved versions thru 1968 and any later variety with the early hinge pin location have limitations when it comes to using them on engines making big power in really fast cars. 

By 1969 they had sorted out the issues with the early units which included moving the hinge pin location to provide superior leverage for a smaller float on the N/S assembly.  They also added POE for the secondaries and got rid of the weighted air door design and used the pull-off to keep the flaps from whipping open too quickly going to full throttle.

They also had the idle bypass system in place by 1969 which is far superior to drilling the throttle plates for big camshafts.

Even with all the improvements folks had been removing factory Q-jets and tossing them aside for aftermarket carburetors thinking they were improving engine performance when in most cases they were not......Cliff

[Cliff Ruggles]

Seldom mentioned in conjunction with this topic are how many excellent factory intake manifolds hit the scrap pile in favor of aftermarket aluminum ones.  Just like the excellent factory carburetors the engineers spent a lot of time with intake manifolds to make sure they provided the best power production over the engines potential RPM range, good idle/off idle characteristics, and efficiency in the "normal" driving range.

Sure you'll read all sorts of advertising about ditching the stock intake for something better that will make more power, but about all that happens in 90 percent of these scenarios is that you remove some weight from the front of the car and kill off some low end power while shifting power to higher rpms where the engine doesn't spend much time.

I get a LOT of attention if/when I take my car to our local track and make a few runs with it.  Last time I went there on a Friday night "test and tune" it was really hot/humid.  In full street trim on DOT's I ran low 7's at 96mph and never even cooled the engine down.  Yep, drove it right off the street, dropped the air pressure in the rear tires to 18psi and started making runs.  I made 5 runs about 20 minutes apart all in the 7.18-7.24 second range (1/8th mile), aired the tires back up and drove the car home.  In staging folks were coming by to check out the combination since I was running WAY quicker than the street cars in attendance and faster than a good percentage of the full race cars that were there.

The look on their faces when they spotted the factory intake and Q-jet sitting on it......PRICELESS!.......Cliff

[Macadoo]

Thanks for the info and great stories, Cliff.  I've read through these posts a few times.  The wife and I just got home from a 3 day weekend at Route 66 Dragway so your last anecdote really hit home.  There was a car show in conjunction with the races and, yet again, I had to defend the quadrajet (even though I'm still working on mine and have the Holley on the motor).  Of course now everyone is all about EFI.  Which would be great if I could afford it, I suppose.
I've hand-milled the base plate and main body so that all three parts fit pretty darn close.  I can't feel any movement with the gaskets in place.  I'v gotten the circuitry and idle tubes tuned to the recipe #2 specs and will start assembly soon.  For right now I'm using parts I had laying around or gleaned from the other carbs because I want to see if I have any air leaks before ordering jets and rods.  The gaskets (for this particular carb) are in fine shape but I'll probably replace anyway.  I've installed 49B rods and #77 jets (a bit rich for recipe #2, I think) along with a G-hanger ans either the short tip CS rods or the long tip CV rods.  Again, just until I know the carb isn't going to leak air.
It was a good weekend at the races and we brought home 2nd place for the GM A-body category.  I haven't won an award in years so that was a nice surprise.

[Macadoo]

Oh, and yes, I scrapped the stock EGR intake for an aluminum Edelbrock.  Rookie mistake, maybe, but I don't think my back could manage a cast iron anymore, lol.

[Macadoo]

Hey Cliff, based on my engine/cam specs, which power piston spring should I try first?  I have all these parts from last summer, when I just started to look into all of this (but before I bought your book).  I've never been able to get it to idle good enough to get a decent vacuum reading.

Cam: .512 in and out, 227/233 @ .050, 110 LSA
CR about 9.8:1
Dual 2.5" exahaust
Cast iron Heads ported and polished

[Cliff Ruggles]

I'm a little confused and not even sure which carb you are using and how it is set-up.

Above you mention 77 jets and 49B rods which would be for a 1974 or early model, not the later Q-jets with the APT system located directly in front of the power piston.  B rods are longer and used in many Buick, Chevy and Olds' carbs thru 1974.......Cliff

[Macadoo]

Sorry Cliff, I've been working on three different carbs, lol.

This is the '81 APT carb from a Checker cab.  I thought I read in your book that the longer rods could be used as long as the APT is set correctly but I may be mistaken.  I'll read over that again.

The gasket pictures I posted earlier were for the carb that I ruined by drilling through the main nozzle.  I wanted to use that one because I knew that it was recently bushed.  It turns out that all three were recently bushed so I'm back to the '81 APT model.

I apologize; I'm trying to do too many things at once because I'm running out of summer.

[Macadoo]

Yeah, I misread the sidebar about the rods.  My bad.  Again, I just need parts in there so I can test the carb for leaks before buying parts.  I'll go with the P rods I have and 74 jets, for now.

[Cliff Ruggles]

Correct, "B" series rods will be too long in the later APT models.

You can use the later K, J, L or P rods in earlier units if you team them up with different style Rochester jets. 

Rochester Quadrajet main jets have the actual orifice much lower in the jets than some other options that are out there.......Cliff

[Macadoo]

Thanks Cliff.  One of the "rebuilt" M4MC units I purchased last year had M-rods.  Aren't those marine?