[gtobird]

My 68 wagon's Quadrajet is leaking when parked. It had a 68 Buick carb (7028240) that had a Pontiac baseplate on it. When I bought the car, my plans were to eventually replace the entire engine with my spare 68 Firebird 400 engine which is complete and correct right down to the carburetor. Since I don't want to replace the engine right now, I figured I would rebuild my Pontiac 400 carb (7028264) and for the time being use it on the existing 350 engine (built to HO specs with 068 grind cam and Ram Air exhaust manifolds).

Of course, Murphy threw me a curve ball. The Pontiac 400 quadrajet has fuel fitting inlet threads that need to be heli-coiled and the shop that is going to do it is booked up for a while. So, onto my quadrajet boneyard. I have another Buick carb which is almost identical to the 7028240 Buick carb currently on the wagon, except it has an Olds baseplate on it and was a factory replacement carb, more than likely built in later years (no date code). Other than having the wrong baseplate, it's a super nice core with nothing wrong with it. So, my thought is to just take the Pontiac baseplate that was attached to the Buick carb on the car, put a kit in it and drive the car until I get the other carb done.

So, what is the issue? Well, the 68 Pontiac 400 carb has idle bypass air on it. Neither of the Buick carb bodies or air horns were machined for it, but.......... the Pontiac baseplate I'm going to re-use from the Buick carb already on the wagon was already drilled for idle bypass air. Basically the idle bypass air was therefore non-operative. Since I'm going to now use the Pontiac baseplate on the better Buick core, it's really simple for me to drill the two holes in the main body cavities and grind the slots in the airhorn to make the idle bypass air functional. The question is whether or not this will be an improvement, or deterrent. The car seemed to run okay without it. Once I grind the slots in the airhorn, I don't think I can go back to making it non-operative.

All opinions are welcome and of course, I've been in contact with Guru Cliff on the build of my Pontiac 400 carb, but thought I would throw this brain teaser on my hybird carb build out to this crowd first.

Old Joe

[Andretti]

I would go after repairing what you have that you know already worked. If you want to avoid getting into a heli-coil repair, another option is the self tapping oversized filter housings (Blue Streak, Dorman) available. Since it's already apart, you can do a good job since cleaning the midbody after is important.
You mentioned it leaking gas after a drive. Those floats are known for becoming saturated so maybe buy one along with the rebuild kit.

[77 TRASHCAN]

Cliffs book shows how to add idle air.

[shaker455]

Originally Posted by gtobird

My 68 wagon's Quadrajet is leaking when parked. It had a 68 Buick carb (7028240) that had a Pontiac baseplate on it. When I bought the car, my plans were to eventually replace the entire engine with my spare 68 Firebird 400 engine which is complete and correct right down to the carburetor. Since I don't want to replace the engine right now, I figured I would rebuild my Pontiac 400 carb (7028264) and for the time being use it on the existing 350 engine (built to HO specs with 068 grind cam and Ram Air exhaust manifolds).

Of course, Murphy threw me a curve ball. The Pontiac 400 quadrajet has fuel fitting inlet threads that need to be heli-coiled and the shop that is going to do it is booked up for a while. So, onto my quadrajet boneyard. I have another Buick carb which is almost identical to the 7028240 Buick carb currently on the wagon, except it has an Olds baseplate on it and was a factory replacement carb, more than likely built in later years (no date code). Other than having the wrong baseplate, it's a super nice core with nothing wrong with it. So, my thought is to just take the Pontiac baseplate that was attached to the Buick carb on the car, put a kit in it and drive the car until I get the other carb done.

So, what is the issue? Well, the 68 Pontiac 400 carb has idle bypass air on it. Neither of the Buick carb bodies or air horns were machined for it, but.......... the Pontiac baseplate I'm going to re-use from the Buick carb already on the wagon was already drilled for idle bypass air. Basically the idle bypass air was therefore non-operative. Since I'm going to now use the Pontiac baseplate on the better Buick core, it's really simple for me to drill the two holes in the main body cavities and grind the slots in the airhorn to make the idle bypass air functional. The question is whether or not this will be an improvement, or deterrent. The car seemed to run okay without it. Once I grind the slots in the airhorn, I don't think I can go back to making it non-operative.

All opinions are welcome and of course, I've been in contact with Guru Cliff on the build of my Pontiac 400 carb, but thought I would throw this brain teaser on my hybird carb build out to this crowd first.

Old Joe

Send your main body that needs a Heli-coil, I can repair & send right back,

[gtobird]

Gents,

Thanks for the tips. Some additional info for you. This story gets messy since I'm playing with multiple carbs.

1.) The Pontiac 400 carb that I want to have heli-coiled already has the Dorman self tapping threaded inlet. It holds decently, but not sure for how long. If it can be heli-coiled, I believe that will be a permanent fix. Since that carb is already getting a complete rebuild, I figured I'd do it all at one time.

2.) The carb that's leaking has a brass float and the float doesn't appear to have any leaks. No matter which carb I use, I will replace all of the usual parts anyway, including the float. The carb that was on the car looks like it has been on that engine a long time. It was literally stuck on the intake manifold after removing the bolts. All gaskets were dried out and crumbling and it still had the original black rubber piece on the accelerator plunger and it was all dried out. It was destined to leak. The bottom plugs already had been epoxied, but I suspect they were leaking too (I did not check) Much better to use the body and airhorn from the nearly identical carb I have as it's in in great conditon.

3.) I have Cliff's book and read about the methods to install idle bypass air. My question was not "how to do it". It was "should I install it"?.

Again, I do appreciate all replies. I'm just a backyarder who messes with Quadrajets every 10 years or so............

[Cliff R]

All Q-jets (at least that I've seen) made from 1965-1968 will be leaking at the pressed in brass cup plugs in the bottom. They corrected that issue in 1969 and few made after will leak.

Pretty much a waste of time to smear monkey chit (JB Weld) over them, but nearly every single one I've had sent here had that done to it and they leaked right thru it 100 percent of the time.

Not a good idea to mix-match parts with a Q-jet. Buick bottoms will bolt to Pontiac center sections, but there are differences in those parts that go far beyond having or not having idle bypass air that can lead to less than desireable results. In any and all cases keep all three original parts together if possible.........

[Greg Reid]

I can vouch for the mix and match scenario. I had problems when I mixed a base plate and bowl from two different carbs that were the same part number. It's like they were mated after all of those years and it always wet the gasket where the bowl met the throttle body. It's a shame too because it really runs great.
I belt sanded the throttle body as far as I dared and never could completely stop the seepage.