RobbMc 1/2" Sending Unit

The original factory fuel tank sending unit on my 78 Firebird came with a 3/8" pickup and 1/4" fuel return line built into it. I was eventually able to get the car to run 12.1's with this configuration using a Holley Blue pump mounted at the tank.

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With the addition of aluminum heads and roller cam there were another hundred horses to feed. The old system couldn't keep up so as a first attempt I purchased a replacement sending unit and had a local gas tank repair shop modify it with a 1/2" pickup line, plus add a 1/2" return line into the tank. The fuel pump was changed to a Mallory 140 and 8-AN lines were run to the front of the car.

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I wasn't totally thrilled with this setup as the return line was kinked where it went into the tank, and the sending unit never did work properly. The electric fuel pump and trash filter are mounted on a custom back plate that bolts to the fuel tank support brackets, this keeps it close to the tank and way from sources of heat.

I first saw the RobbMc 1/2" sending unit mentioned on the Poncho list and decided to check it out - it is a nice unit! A comparison with the cobbled unit it replaces gives a good idea of the quality. I ordered it with 8-AN fittings so it would connect directly to the existing pump and return line.

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One small issue during the installation, the sending unit didn't want to seat in the tank opening, a few measurements gave the reason, my tank is 9" deep at the flange, the sending unit was 9 1/4" long. I removed a little over 1/4" of the pickup tube so there would be a bit of clearance with the bottom of the tank. The tank is the original factory one and the sending unit is directly above an area of the tank that has a 1/4" high indentation.

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Once shortened the unit slid right in, a couple of adjustments and the outlet connections were exactly where the old set up put them so it was an easy bolt up.

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The filter and pump are just below the tank and very close to maintain clearance from the rear axle.

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Almost hidden exhaust pipes :)

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Good news - the RobbMc sending unit is more accurate than the original factory one which left me stranded a couple of times with no gas while 1/8 tank was still showing on the fuel gauge. The RobbMc shows 1/8 full with 4 gallons in the tank ( a nice cushion!) and when completely full the gauge is right on the full mark, the original would stay above full for about 50 miles of driving.

Overall the unit is excellent quality and was an easy install once I shortened the pickup a little. For more info you can go to this site:

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