I rebuilt my Quadrajet this past winter with parts from Cliff. There are some problems though, my motor is a modded pontiac 400. Before I parked the car this winter it drove okay and was a little lean on the primaries and secondaries. This winter I rebuilt the carb and put Ram air manifolds on it, should be faster right? no.:(

The car was opening the secondaries really early, now I think its a little closer. The bigger problem is, is that its burning a lot of fuel at idle and part throttle. While idling it will drip out the tailpipes and when backing into the garage just barely tapping the gas to keep it around 1500-2000 you can see fuel smoke and smell it.

I can't figure out what to do. Is it possible that a rod is not seated in the primary or secondary? I'm stumped.

BAD FLOAT,WRONG FLOAT LVL,DIRT IN CARB/NEEDLE & SEAT,TOO MUCH FUEL PRESSURE,ARE A COUPLE THINGS THAT CAN MAKEIT RUN RICH.

Also,if the power piston poped out of its vacuum chamber it willl eak vacuum and also pull the prim meter rods out of the mains which will makei it run rich yes at idle and off idle because a little of the idle fuel is drawn through main from what i had read in moding the q-jets buti have no way of verifying it so dont shoot the mesenger.(LOL!!!!)

Lastly,are you running correct power piston spring for cams idle in gear with auto trans & just off idle intake vacuum ? If not that too can cause running rich issues.

But as you asked/wondered no its not likely a secondairy rod/s is not seated,that would be a very rear thing to happen unless something is screwy with the sec road hanger or the upper sec air blades are getting hung up and not returning to base point.Its much more likely an issue with something on/in the primary side of the carb IMHO.

I have to ask this,the choke blade isnt stuck closed or partially closed resulting in the rich mixture because that will also cause a rich mixture.

TYPOS' TYPOS' , MAN I AM REALLY BAD TODAY/WORSE THEN NORMAL(LOL!!!)

Scott

Wow, lots of things there. If the float level was set to high would that cause it? Also there is no choke on the carb, no top butterfly on the primaries on it either.

Float would the first thin i look at,and from what you said it sounds just like a float set to high.After you get the float right go back and adjust the mixture screws again.

YES,THE FLOAT LVL WAS 1 OF THE 1ST THNGS I SUGGESTED YOU CHK OUT,try a 5/16" float lvl. A 1/4 " float lvl is rec for may q's but when having flooding issues 5/16" is a little more conservative keeping the fuel lvl int eh float chamber a smidge lower/less which should work fine too.

I mentioned lots of things because there mult tings that can cause a rich running q-jet or almost fooding in your case since you suspect raw fuel is comming out the exhaust.

If thats the case pull the dipstick and smell for fuel contam in the oil . If you smell fuel in the oil change it asap because the fuel in the oil will decrease it's ability to properly lubricate the engine. BTW,a bad mech fuel pump diaphram can also pump fuel into the crankcase,not just a rich running or fooding over carb.

Scott

I’ll ask, not related to your question … but with no choke, have you also modified the fast idle lever / secondary lockout? Without some change, you’ll be highly disappointed to know that your 4bbl won’t operate! Removing the choke on a Q’Jet is a pretty serious change … Are you trying to get more air through it? Or, Just don’t have a choke hooked up?

Related to your question though … it sounds like a modified setup. Have you also installed a high volume fuel pump and/or pressure regulator. Modified to a higher than stock fuel pressure (lower psi than Holley) can cause the needle/seat not to close, and modifications to the float height.

Get yourself a package of JB Weld. Drain the gasoline out of the carb. Get your carb and yourself to a comfortable place where you can work on it.

#1) Drive the accelerator pump pivot arm roll pin in towards the air horn. While doing so leave the pin out just far enough to release the green pivot arm but not so far that you cannot get something thin but sturdy between the roll pin and the carb air horn. This will greatly ease putting the roll pin back where it belongs when you reassemble the carb.


#2) Remove the two LONG screws at the upper rear of the carb. Do NOT remove any other screws from the top of the carb.

#3) Invert the carburetor.

#4) Remove the three screws that hold the throttle body to the carb body and remove the throttle body.

#4) Locate ALL of the LEAD plugs in the bottom of the carb body. There are roughly 5 as I recall.

#5) Uncap and squirt on a piece of cardboard equal quantities of BOTH of the JB Weld tubes such that they both together make an unstirred puddle roughly the size of a quarter.

#6) Mix the black and white puddle of JB Weld until the entire puddle is uniformly gray.

#7) CAREFULLY cover each lead plug with the mixed JB Weld until there is NO lead showing.

#8) Be very sure to clean any excess JB Weld from around the two large plugs that are roughly located in the center of the carb body. They fit into a well in the throttle body and they are a tight fit. Any excess JB Weld will make it hard to reassemble the throttle body to the carb body.

Additionally be careful that you don't get the JB Weld on any mating surfaces. If you do, wipe it off before it hardens. If you let it harden you can scrape it off with a utility knife so don't panic.

#9) Let the JB Weld harden fror several hours. It helps to set the carb body in the sun while the JB Weld hardens.

#10) Reassemble the carburetor in the reverse order that you took it apart.


This may sound complicated but after you are finished you'll agree that its a pretty simple thing to do.


I have no way of knowing if your carburetor leaks from any of those lead plugs but its a known problem for which Rochester never came up with an effective fix. If this is one of your problems, doing what I told you to do will instantly and permanently cure the issue.

If you handle the carb carefully none of the adjustments you made when you rebuilt your carb will be affected.

Does this car have a stiff cam? What kind of vacume is it pulling. This sounds like "Nozzle drip at idle and can be fixed through a few modifications. What rpm does it idle at? If you have to bump up the throttle blade to make it idle then a lot of bad things are going to happen with off idle bleeds and things to make it run pig rich. Get it to idle and take a flashlight and look inside at the venturis and see if there is fuel coming out of them. If so you will need to do some modifications to prevent this. Until you do it will never run correctly at idle.
Bill

If thats the case pull the dipstick and smell for fuel contam in the oil . If you smell fuel in the oil change it asap because the fuel in the oil will decrease it's ability to properly lubricate the engine.

Scott

Off topic a bit. Last winter, installed a Q-Jet. I guess the plugs were seeping.
I started to get knocks and rattles. I checked the oil....smelled like gas. I put the 600 Holley back on, did an oil and filter change. Still had noise. I ran some ATF (added a pint) in the engine for a few hundred miles, changed oil and filter again. Noise went away....whew. I can't say enough about not only checking the oil level but to smell the oil for sign of gas contamination.

Lots of good info above, I will add "how much fuel pressure does it have?" I had Sean Murphey build my Qjet. bolted it no and idle was not right, called Sean, he ask the above question, said, bet you have something in the 7's and Qjet will not handle more than 5 1/4PSI. I added a pressure regulator and gauge, it had 7 at idle and ran up to 10 reved up before I regulated it down. Even at 6PSI the idle was going up & down as it spilled gas in. set it to 5 and idle was smooth.
Back to the choke, my view, if you took it out that is to sacrafice good driveability to get a bit more power?
A: If your priority is brute power go get a Holley,
B: If your priority is drivability run a Qjet and if thats the case you need to put the choke back in

For anybody working with a Quad you need this info.
Scroll down till you see
"Lars Quadrojet tuning paper" in double lines.

http://wiki.corvettefaq.com/index.php?title=Intake

Nozzle drip will definitely cause rich running condition. You might need to work on the idle circuit or add some bypass air.

The car has a fairly large cam in it. I worked on the idle circuit, installed bigger tubes like Cliff said etc.... Also drilled out the two .110 diameter holes for air. I put the idle screws in and only backed them out 2 turns. The car won't idle unless the primary blades are partially open. The car also has a carter pump on it, I think its 120 gph. I will check the float level as soon as I get a chance.

Did you follow one of recipes to the T in Cliff's book? What size did you go to on the idle tubes?

I believe the idle tubes are .037.

Wow, that is one seriously modified Q'Jet! You did understand when modifying it ... that it's best to work slowly, as the modifications can't be un-done?

After reading your last post ... I do think your primary problem is in sorting out the idle circuit. You'll want the throttle blades to be able to completely close.

I'd still look at ... I think the fuel pump is too high pressure, and I'd still want a function choke mechanism.

Neal

Luke,what size is the motor and what are the exact cam specs like dur @.05,LSA,gross lift?

You say its a fairly lrg cam well whats a fairly large cam in what motor?

When it comes to q-jets when you get to approx 228-230 deg dur @.05 thats when you have to doa very minor/minmal drilling tweak to the idle down tubes for a littl more fuel to help it idle with perf cam. But you dont need to drill much and maybe you over did it and thats why its runnign rich which is why i am asking for exact cam specs and motor size.

We also need to know what the prim jetting and rods are along with what power piston spring is being run.

And lastly whats the idle vacuum with auto trans in gear ?

We need to know this stuff to better help you so get cracking.(LOL!!!!)

Scott

What Scott said... Need more info and what carb? I've been building alot of qjets for local racers with cams in the .030 @ .050 duration range. I've found that usually I can get by without opening up the idle tubes much dependant upon what the carb originally came on. You could always pull some idle tubes out of a old carb or get some new ones from cliff if they are too big. Keep in mind fuel pressure and float level affect the entire calibration. Small steps on mods. I wouldn't get real hung up on exact position of throttle plates as long as there's no nozzle drip.

How far are the throttle blades open? Did you change any gaskets when you worked on it?
Some gaskets won't allow for idle air bypass.

Well theres no nozzle drip.:) I checked that.

Here are the motor specs:

Pontiac 406
9.5 compression
cam-288advertised,230@.050, .480 lift, 110 LSA
Ram air manifolds with dual 2-1/2" exhaust
MSD HEI

Not sure on vacuum but I have the idle set at 1000-1100 when warm. It won't go much lower and the brakes start to get hard.

I took it for a spin and when it got to about 3K I punched it and it pulled great other than a slight blip once in a while like to much/little fuel. I had my dad follow me and when I tried flooring it a little black smoke came out before it took off.

Have you checked the float level or tried turning the idle screws in? On mine when I opened up the idle tubes I went from about 3 turns out to a 1/2 turn.

FYI,that slight BLIP as you put it when you get the rpms up to 3k in st then nail with a q-jet is likely the upper secondary door opeing a littl too fast causing a momentray bog with the big gulp of air it get leaning out the mix untillthe secondary fuel cathes up with things .

all you need to do is adj in approx a 1/4-1/2 tunr tighter on the upper sec valve spring and that bog should go away or darn close toit with maybe one more 1/8-1/4 turn tighter past the 1st adj.

The blk when you hit it could just be carbon in the exhaust being spit out.

Scott