I'm getting 5 mpg with a 318???

[drobertson]

Over the previous year, I've rebuilt the 318 in my 1973 Charger, along with the transmission. Some mods I did was long tube headers, dual exhaust, summit .454 lift, 272 duration camshaft, 340 springs, edelbrock performer intake.
Last few days I ran an edelbrock 600 cfm carb and got 2.5 miles per gallon, yes you read that right, two and a half miles per gallon. In about 50 miles after filling up my tank, it was nearly empty. So I put a 500 cfm edelbrock carburetor, and now I get 5-10 mpg. What could be my problem? I have confirmed timing at 14 degrees advance, all new stock replacement electronic ignition components, it shifts fine and the kickdown works. I plan on intalling an EFI kit when I can afford it, but I'd like to get better mileage out of the carb if I can until I've saved my money.

 

[GetX'd]

Yikes! You definitely have a problem. I was going to make a joke about then I realized what a bummer it must be. Good luck.. If someone doesn't chime in you might consider have the car put on an analyzer. It will cost you a few bucks but with what you're paying in gas it would be worth it.

 

[drobertson]

Yikes! You definitely have a problem. I was going to make a joke about then I realized what a bummer it must be. Good luck.. If someone doesn't chime in you might consider have the car put on an analyzer. It will cost you a few bucks but with what you're paying in gas it would be worth it.

I'm in the middle of a lowest populated state that happens to be huge : Wyoming. In other words, It would be a 3+ hour drive to a place that can do those.

 

[QQBlue1]

I was once driving my Charger through Wyoming and had a leak in my fuel line and nearly ran out of fuel. Perhaps something similar is going on with your car such as a bad seal or gas line?

 

[drobertson]

I was once driving my Charger through Wyoming and had a leak in my fuel line and nearly ran out of fuel. Perhaps something similar is going on with your car such as a bad seal or gas line?

I will check and get back to you on that.

 

[Bb70charger500]

My first charger 74 used to get extremely bad mpg with the 318 I found out later that the rubber gromit that seals the filler neck was toast and everything leaked out and the stuff below the level sloshed out . A $10 part wasted so much gas

 

[hangn0ut]

A leaking fuel pump can put fuel right into the crankcase.

 

[mopar 3 B]

If it is actually using that much fuel what color is the exhaust pipe? That unburned raw fuel must be burning the eyes. Are the sparkplugs burning clean or are they fuel soaked.
Gas cap in place?

 

[furryfrog]

You said your timing was at 14 degrees? Is that your initial timing? What is your total timing and at what rpm does it come in at?

A wideband o2 is a useful tool in your situation.

 

[mrsnicks]

I just rebuilt a 318, put in a stock 340 cam, 4bbl holley streetmaster intake, 1406 (650cfm) edelbrock carb. I get 15+ mpg if I keep my foot out of it. Like other people have said check your gaskets, and hoses on the vents of the tank to the evaporator.

I was behind my Charger while it was being towed to a shop to put on exhaust, and I hadn't capped or plumbed the vents to the evaporator. I couldn't believe how much gas was sloshing out when he hit a bump, and it wasn't even full.

Patrick

 

[drobertson]

My first charger 74 used to get extremely bad mpg with the 318 I found out later that the rubber gromit that seals the filler neck was toast and everything leaked out and the stuff below the level sloshed out . A $10 part wasted so much gas

It has a new gas tank w/ a new grommet for the filler.

 

[69a100]

It has a new gas tank w/ a new grommet for the filler.

That doesn't mean a gosh darn thing if gas is still pissing out of it. Good Luck

 

[idrivemopar]

I think you have a gas leak somewhere, I am running a Crane 272 cam in my 340, same specifications as your cam, and my timing is at 19, total timing is about 38, and not using vacuum advance, and my mileage is pretty good, don't know it for sure, and I am running the big version of the Thermoquad.

 

[HawkRod]

I agree with folks saying to look for leaks. I was only getting around 15 MPG with my fuel injection and new tank and then I discovered that the tank was pushing fuel out the vent. I would fill it up with gas and then check it carefully. With that low MPG, you must be losing fuel somewhere. Check fuel lines, gas tank vent, filler tube/grommet, fuel pump, etc. Basically anywhere that has fuel.

Good luck.

 

[19polara64]

You might try a leak down test. That would tell you if your engine broke in right or maybe some other problem not allowing proper pressure.

 

[moper]

It's more than likely the ignition timing curve. "Timing" is a combination of the initial, the mechanical, and the vacuum advance numbers. You have 14° initial. What is the total without the vacuum hooked up? What is it with it? You should know those two figures, and you should have the vacuum advance connected given the setup. It's more than likely a tuning issue.

 

[threewood]

You are losing gas either out the exhaust, into the crankcase or from external leaks. If you are rich the exhaust will burn your eyes. If there is an external leak, you will smell gas around the car especially in your garage. If your oil level goes up, mech fuel pump is probably leaking into the crankcase. How did you calculate mpg?

 

[kiwigtx]

There has to be a leak somewhere in the fuel system...a few years ago I was getting 6 mpg on a poorly tuned 6BBL on a trip.

 

[drobertson]

Well... I figured out the issue. My hose connecting to my fuel sending unit had come loose and was spraying fuel out. Now it's doing much better!

 

[kiwigtx]

Good catch.