Duel Power Piston

[lightning boy]

I have a Qjet from a 74 Pontiac that has the aneroid valve in the front with two power pistons. One controlling the primary metering rods, and another controlling an additional rod.
I have never worked on one of these before. What were they for and can they be modified for street use?

[Cliff Ruggles]

Pontiac carburetors didn't use that arrangement.

What is the carburetor part number?

[lightning boy]

It's a 7045184

[Cliff Ruggles]

Without taking the time to look it up I'm pretty sure that's an Oldsmobile Q-jet, not one from a Pontiac engine.....

[Burd]

My carb booth says Old’s, 1975, 455, w/ AC, delta, cutlass, ambulance, and hearse or Hurst for the dummy’s that say that. 

[quadrajam]

A long long time ago I tackled one of these. I had to convert it to conventional
metering rod setup and it actually ran well. The problem was that it had multiple
primary well plugs and leaked so bad I scrapped it for parts. Instead of aneroid
they should call it hemorrhoid because it was a PIA.
Can be done though.

[Cliff Ruggles]

With some work you can convert them to the later style APT but this does NOT correct the fundamental flaws with the design.

I recommend in most cases to move to a later unit in the first place.

The only time I'll tackle one of those variety is when it's a numbers matching restoration and even then I try to stay clear of them.....

[lightning boy]

Okay, thanks guys, I'll use it for parts.
What were they for? and what are the flaws?
Just trying to learn something.

[Cliff Ruggles]

The flaws are many and too lengthy to go into great detail.

Right to start with that APT simply puts fuel under the jets, so fattens it up everywhere. 

The flow path from the APT jet/rod is unequal in length.

The flow path requires a common connection between both jets.

ALL of it is at the bottom of the carburetor where all the water, dirt and debris would go.

That's the short version.........