New to the 304 scene...

I just picked up my second Jeep, a '73 CJ5 about two weeks ago. She ran a bit rough but starting with new plugs, wires and a quick tune of the carb she's considerably better. Here's my problem. The gas mileage is through the floor. Mind you this is my second Jeep so I know full well that they are not economical but this is a bit off the wall. I filled up my tank yesterday about 12 gallons or so (my gas gauge is dead) Put 52 miles on it and she left me on the side of the road with a gas can. Roughly 4 mpg? Is that even close to right? I've never had a vehicle with an engine this large but from what I've read even these yield mpg's in the mid teens or so. This was the first time that I had the money to toss in a full tank of gas to judge the mileage on.

Bit of back story. When I tuned up the carb (the PO had the thing really cranked up) I also checked the fuel line between the pump and the carb. It was dry rotted at the clamps. So I replaced it. It ran so I was happy. Now that I'm in for a 12 hour work day I can leave her parked and run out to check for any mysterious puddles underneath. If I can't find a leak are there any other places to look, any other advice you might be able to offer up??? I can do damn near anything frame and body work wise but when it comes to engines I'm out of my league.
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Well.....I am some what new to the 304 also. As you already know your mpg is way off the base line. I seem to get around 15-17 with my 304 using a motorcraft 2100 carb. What carb is on your 304? I am thinking a leak along with carb issues is what you are looking at. Others with a better know how will chime in.

Kent

 

I'd check the fuel pump and see if it is pumping fuel into the crank case. You said the rubber fuel line was dry rotted which is indicative of sitting for a while or not being run often. Same thing can happen to the diaphragm in the fuel pump. Pull the dipstick and smell the oil. If it smells like fuel and the oil level is high you need a fuel pump. Using that much fuel in a 304 you should be getting black smoke, fouled plugs, and or unburned fuel out the exhaust unless it's leaking somewhere. Nickmil

 

If it's the stock carburetor (Motorcraft 2100), they are notorious for having a punctured power valve diaphragm. That will make the engine run rich, but I'm not sure that this would be enough of a fuel drain to use as much fuel as you did.

As Nick mentioned, I'd suggest you look at your spark plugs - they should be sooty black and possibly wet with gasoline if all that fuel is going through the cylinders and out the exhaust pipe.

Also, if you are using that much fuel, I'd expect the engine oil will be diluted with gasoline, and you could smell gas in the oil. Even if the level is ok, I'd change the oil.