Packard Forum Index » V-8 (1955-56)

My Clipper with od gets about 18 on the highway but only about 12 in city driving.
After I rebuilt my 55 Caribbeans engine about 6 years ago, I filled up the gas tank and drove it about sixty miles. About 1 mile from home, the engine died. The gas gauge didn't work but I thought it could not have possibly run out of gas. I checked everything I could think of on the side of the road with 100 degree temperatures and no tools. I called AA and had the car towed the final mile home. Sure enough, the thing was out of gas. I guess I got about three miles to the gallon. The car was running poorly, the carbs I was using were not the Caribbean carbs but old carbs I had laying around. I removed the dual carbs in favor of a single quad. It runs fine and gets much better mileage now but nothing spectacular. Probably about 14 on the highway. I did find a pair of 55 Caribbean carbs and am now going to have them rebuilt. The dual quads will remain off unless an important show is involved

The best mileage I ever got on Best Other was 17.? and I doubt that as I was running 235/70 R15s. I got 15.? running up and back to New York state last year. I ran between 65 and 70.

Worst I own is 75 T-bird w/460 PI. Gets 6 to 8 mpg, but all six are great!

Just filled up my 56 Patrician today.Combined highway/city driving-14 MPG.

The 14.4 average for city/highway driving corresponds to what I've been experiencing with my '55 Pat for the past 14 months or so of daily use. Recently bought another car so I could let it rest a little.

I just filled up my 38 coupe tonight - 14 MPG. That's mostly short drives going to cruise nights

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I wonder how much a missing copper washer, causing fuel to slightly leak onto the intake manifold, would reduce fuel economy 🤔

Quote:As you learned, the correct dual quad carbs are very different from the random single 4-bbl, but not 5X worse. You had junk carbs pouring raw fuel down the intake.

FWIW, I've used professionally rebuilt single 4-bbl carbs on a Caribbean intake and with a direct reading O2 meter seen them producing ideal air/fuel ratio at cruise.

Where the major difference is at idle and deceleration. The single 4-bbl has four idle passages. The correct dual 4-bbl carburetors plug the secondary idle passages, so the manifold sees only four, not eight idle passages. With all eight idle passages functioning, the air/fuel mixture will go dead rich on deceleration, wasting a lot of fuel.

Also, the procedure for adjusting idle is critical and there is a Rochester Technical Bulletin which shows step-by-step how to correctly adjust the idle.

As you probably know, the 1955 Caribbean carbs are quite different than the 1956 versions.

jack vines