Art and the Quadrajet

We bought our 1987 Rockwood in November of 2011. It was a derelict about to be parted out by the new owner. The tires were high end Michelin X tires all dry-rotted to hell. The right front blew out on our way to the tire store, blew out only three miles from where we purchased our new home. All of the comfort systems were dead.

1987 Rockwood. aka Home

1987 Rockwood. aka Home

We’ve been dealing with systems issues on a priority basis since then and finally got to the engine. Our Chevy 454 has been misfiring and wasting fuel at prodigious rates and a new coil, plugs and plug wires twice as I hit the plug wires with a MAPP torch while plugging off the A.I.R. plumbing. But ignition repairs did not correct the misfire. So I began my diagnostic and repair journey by disabling the emission control systems that would directly effect the engine’s ability to run smoothly. First I disabled the exhaust gas recirculation , then the throttle controlled ignition vacuum advance without seeing any improvement. I posited water in the fuel due to phase separation and started adding fuel to the main tank 20 gallons at a time with a bottle of water remover each time, running the tank as low as I dared. I believe I still have entrained water problems but because it was cheaper than adding a possibly effective Wix fuel filter and water separator I chose to open up the carburetor, a truck Quadrajet number 17985212.

Going in well read and thoroughly prepared, I found the fuel level 1/32′ low at 7/16″ so I raised the fuel level 3/16″ to 1/4″. 1/4″ is within the established fuel level range of Quadrajet carburetor fuel levels and I arrived at this figure by bending the float. The first bend brought the fuel level up 3/16″ so I left it alone. I’m only making educated guesses here so there is no reason to be getting fussy with multiple bends back and forth for some other semi-randomly chosen value until I have some idea where I’m heading. Raising the fuel level tends to make the overall fuel mixture richer, something I wanted to do, and makes it easier for any entrained water to pass through the system. Next I raised the adjustable part throttle adjustment which for all practical purposes is the lean stop for the power piston so the lean cruise fuel mixture would be just that much richer. I also removed the plug over the power piston adjustment and the power piston rich stop so I have easier access to the lean stop adjustment. Allstate Carb and Fuel Injection in Islip, NY provided a pair of airhorn gaskets and after I gave up on finding the power piston return spring, a new power piston return spring. So this means that on the way to the end of this particular journey I drove the Rockwood for a few days with the power piston permanently at cruise lean because of the missing spring. The fuel level adjustment and the 1/2 turn enrichment on the power piston stop seems to have eliminated the misfiring driving around at cruise lean.

Entrained water still collects at idle but it is easily cleared upon acceleration. Adding the power piston back onto the mix has added smooth power that I haven’t felt since we put this old man back on the road. Now to drive for a while and check the exhaust color and fuel economy!

O-kay, I’ve run through twenty or so gallons of gasoline and find that the fuel mixture is still lean. Really lean on the secondaries, pop back through the carb lean and lean surge lean on the primaries. What I should do is drive around with the engine over off and the air cleaner removed and a soda straw sitting on the power piston. Then I can find out the vacuum level the power piston opens at and get a better idea if I need larger main jets or not. But not at these outside temperatures. The outside air temperature is still hovering around 0F. So that’s what I’m going to not do. I have found that with the higher fuel level the choke vacuum break needs to open the choke about twice as much as it dies now. So what I am going to di by guess and by gosh with some seat of the pants windage thrown in is tighten up the spring on the secondary air valve and open the primary lean cruise another one-quarter turn. And readjust the vacuum break.

About Art

55 years old. By training, ability and experience I am a master toolmaker. My most recent projects include designing and building a process to grind a G rotor pump shaft with four diameters and holding all four diameters within plus or minus 4 microns of nominal. This was an automated process using two centerless grinders refitted to my specifications using automatic load and unload machines plus automatic feedback gauging. I also designed and built an inspection machine to check for the presence and size of a straight knurl on a hinge pin using a vision system for non-contact gauging.
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