1970 fury3, I'm getting about 8mpg I don't know anything about what may be in the engine so I assume its stock but i may be wrong seeing as the previous owner who i bought it from added huge traction bars and had a racing build 727 in it that was completely seized up. Anyway what it has is a 4bbl edelbrock carb, dual exhaust with headers, standard build 727 with a cheapo torque converter(had to replace the old one because the previous seized trany also tore it up). I do not know the rear end gearing or how to figure that out, I'm still learning. The car was idling at 30mph i played with the idle screws and got the idle down as low as i could without it stalling and it now idles at about 24mph so i will see how much that improves fuel economy. The 8mpg was using half the time on highway and half the time in city at the 30mph idle over the course of 100miles, no lead foot. Question would be does this sound even close to normal and any suggestions?

 

Sounds like you have a vacuum leak? Causing the engine to run too fast. Or it has some kind of BIG cam ?? A stock 318 you should be able to idle it down to 500 RPM's before it stalls

 

Sounds to me like "some kid" overbuilt the thing. Without knowing ALL the engine particulars, you or I cannot ever know.

If it has a big lopey cam installed, it will never get mileage

Depending on what intake and carburetor is on it, that might be hurting you

Timing, meaning, initial, distributor advance curve, vacuum advance all affect mileage greatly

You DO need to figure out what you have for overall gear ratio There are online calculators, so start by Googleing one



http://www.google.com/search?hl=en&s...l2-1.12.6l19l0

If you have a tachometer, you can note your RPM at a given speed, say, 60mph, and plug your tire size into a speed calculator

To figure your rear gear directly, try this:

Block the front wheels for safety, and jack up ONE wheel. Release the parking brake, put the trans in neutral, and try to turn the tire. If you can turn the tire, this means you do NOT have a limited slip rear axle.

So now, turn the tire TWO full turns while carefully counting the driveshaft.

If the driveshaft moves 3 1/2 turns or a tiny bit more, you have 3.55. If it turns 3 3/4, you have 3.7x (These will depend on what series rear axle you have)

If the tire will NOT turn, you have a limited slip (suregrip) axle, and so you'll have to jack up BOTH rear wheels, and turn one of em JUST ONE turn while counting the driveshaft.

I have to tell you, this is a long, tough road. It is much harder to diagnose problems such as this when you don't know what you are starting with

 

I did originally have a vacuum leak and replaced the gasket under the carb and went from 6.7 to 8mpg. I already checked the vacuum line, no leak there.

I've been meaning to set the timing but haven't got around to it and I have no tachometer.

The manifold is an edelbrock with a edelbrock 1404 or 1405 series carb.

Previous owner told me the rear axle was a positive traction and that's all I know about it. I can get a jack under it later this week and see the gearing.

 

Yes but WHICH Edelbrock and WHAT carb?

Easy to tell, just LOOK (or post a photo)

All Edelbrock manifolds are identified somewhere on the manifold with a casting model no or name

If you have a "performer" or something similar, GOOD for low end torque and mileage

If you have something else that is a high RPM performance manifold, it might actually HURT mileage.

You can ID the carb easy. Just look at the front of the carb, the number will be stamped right there, on the passenger side front mounting ear

1404 is 500 CFM, 1405 is 600.

Both are manual choke and are sold "as built" "for performance" rather than mileage. HOWEVER there is no reason, if jetted correctly, that they cannot get good mileage. And that brings up something else-----has someone played with the jetting/ metering on your carb? That could be a big factor

Here's "the book":

http://www.edelbrock.com/automotive_...ers_manual.pdf