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'69 442 Quadrajet is leaking at the base on the driver side. I can also smell some gas while driving. Pics attached were taken after 2 short drives (say < 7 miles each). I cleaned the side wall of the manifold first to get an idea how much it is leaking, so the residue is after just two drives. Carb bolts are tight, a little tighter than 15lbs. I have taken this carb off once or twice with this gasket (which is/was new).
So, I am wondering if I should just replace the gasket and see what happens, or if there is something else going on here? The upper gasket is not leaking, just the lower. The carb is clean. Looks like the leak is just from the lower gasket and just on the driver side (front, back and passenger side of carb are all clean).
Leak is below the throttle and front part of spring down the manifold side (light stains) Leak is below the throttle and front part of spring down the manifold side (light stains) Residue from leak after two short drives.
I never had luck reusing carb base gaskets. The ones with the nylon inserts in the bolt holes are designed to crush when the bolts are torqued and there is no crush left when reusing them.
I’ve been working on qjets this week, so this is a timely question. What started as a sticky @WOT turned out to be a bent primary rod. But on the way I redid a bunch of qjet bases with bushings.
You may want to experiment with different base gasket thicknesses. They have the thin Mr.Gasket ones and there are also the thicker (heat insulating) 1/4” ones with the plastic inserts. I like the 1/4” thick ones, but I don’t have much luck reusing them either.
You can find these gaskets at quadrajetpower.com or I think qjets.com too.
I never had luck reusing carb base gaskets. The ones with the nylon inserts in the bolt holes are designed to crush when the bolts are torqued and there is no crush left when reusing them.
Agree. I buy my base gaskets & rebuilt kits from Cliff.
Is it coming from the forward throttle shaft? Look down the primary venturi with engine idling and see if any fuel is dripping out of the venturi booster (you may need a flashlight). Check to see if fuel is seeping thru at the forward throttle shaft. Also rev the engine a few times and see if the accelerator pump is shooting 2 good streams of fuel.
I just got through rebuilding 4 qjet throttle plates. All of them needed primary shaft bushings. All.
I’m a hobbyist, but here’s what I learned:
I got back into qjets this Summer since I had a throttle sticking open (oh sh*t) when I nailed it to WOT. I thought it was secondary butterflies interfering with the back barrels, but I was wrong. Cleaning & polishing secondaries didn’t help. They were fine. It turned out to be a bent _primary_ throttle shaft which would hang up right near WOT. Cuz when you nail it to WOT, the primary shaft rotates to an extreme position, simultaneously driving the secondary shaft to WOT. The throttle plate may also be bent from over torquing. Either way it wasn’t right.
What was weird was that unless I nailed it to wide open, the carb was perfectly behaved. When I drove it gently, the carb was just great. But nail it, and it would hang up open & stick @2,000 RPM. Took me 3 weeks to find the bent primary throttle shaft & possible bent throttle plate. I’m not sure how to straighten the shaft, so I’m grateful to have a spare. Or 3. Using a spare now and it’s fine.
I agree with the possibility that it’s the primary throttle shaft. The gas leak path / evidence would look identical to the drip you showed.
The quick check is a blast of Berryman’s B12 Chemtool shot precisely at the drivers side primary shaft hole in the throttle plate. If the idle rises, you’ve got a vacuum leak. If not, you’re good. You can also use starting fluid for this test. Basically, shoot the stuff where you think there might be a leak. If the RPM’s rise, you have a vacuum leak.
If you’re driving the car, your primary shaft is wearing on the throttle plate, or a bronze/brass bushing which has already been used to repair it. Every time you touch the gas pedal, you’re rotating the primary throttle shaft. Eventually it will leak. Mostly this shows up as a vacuum leak and/or an erratic idle.
Within limits, you can cover a primary shaft vacuum leak with an idle screw adjustment. But I’m guessing it can show up as a gas leak too, probably not when the engine is running, but after shutdown when the gas is not being sucked into the block.
I’ve never seen a qjet make a leak like what your photo shows, the proper fix is probably a quality rebuild or fresh qjet from Cliff Ruggles, Sparky Kalkhoff, SMI or other good rebuilder. Used to be that redone qjets were $500+/-, these days it’s closer to $700.
I'm assuming your throttle body plate screws are tight. That puddling does appear it likely is coming from the shaft. Maybe when the car is off and hot perhaps? When the fuel might be expanding into the carb primaries and dribbling along the shaft and out of the carb onto the manifold a bit? Or giving it a pump shot or two when cold starting. Hard to tell without babysitting it.
You can also use propane torch gas (unlit, of course) and rig up some sort of smaller tube/hose to the outlet to just allow the propane to be concentrated to a small area, and hunt for vacuum leaks that way. If you find one, it'll increase RPM a bit just like the spray stuff. Good thing is you can do the entire manifold for vacuum ports and all sorts of stuff without getting spray all over the place.
Take your return spring off and the throttle cable wiggle the primary shaft at the throttle cable side. This is where the throttle body sees the most wear. If you can hear it clunk or seems like it's pretty wobbly such as seeing it actually move in any direction besides rotational, then you probably need to re-bush the primary side. The secondary side normally doesn't need it, but sometimes they might, so check everything. It's not a tough thing to do, but rebushing a throttle body takes a tad bit of skill to do it correctly. Plus, a reamer tool would make it easier. That's a whole 'nother subject.
If you're mechanically handy, a stock Quadrajet rebuild is incredibly easy to do. It's a tad more complicated if you had a computer controlled one, but those aren't that bad once you understand them.
July 9th, 2022, 02:37 PM
