Only 7 MPG - City

[BillT]

I’m getting about 7 MPG on my 64 390, mostly in the city and not jumping off the line. I expected to get about 9 – 10 MPG, so the 7 MPG seems really low. Using premium gas, and cannot find any leaks, i.e. tank to carb. The air cleaner filter looks clean (white). The car idles smooth and the auto choke is wide open (after a short warmup).

So my questions are – what is the normal city MPG in these TBs, and if more than 7MPG, what may be my problem.

Thanks

[scumdog]

10+mpg here - but our gallons are bigger.

[BrianC]

MPG factors---Is your tire size the same as original, or very close if you have metrics? That could throw it off. Also the speedo gear in the tranny could have been changed also. Check those by finding one of those digital 'YOUR SPEED' radar displays the cops put on roads and compare your speed to the radar. If your carb power valve is the wrong one it could come in too early, that could do it. Is you vacuum advance functioning? Put vacuum on it and see if it holds vacuum and moves the points plate to advance timing.

[Cliff Rankin]

I also find that my 64 does a lot worse on
Gas mileage than my 63. Same drivetrain.
But the 64 seems to have a lot more punch.
I'm planning on putting my old " tom tom"
In the car to check it. I found it to be pretty
Acurate when I used it in the family car.
The Lincoln was 2 mph off.

[sseebart]

Seven mpg is a little lower than expected, but (for me at least) not enough to start tearing apart an otherwise good running car.

I drove my car daily when gas was over $4/gallon, and it was painful--I average 8-10 mpg (city).

~Steve

[Joe Johnston]

But the 64 seems to have a lot more punch.

Compare the tire sizes and more importantly the differential ratios

[mnpetri]

I tried to calculate the mpg with our 65 the first year we had it, the speedo doesn't work so I was using the distance from my bing-generated directions.
On a straight highway trip, I figured just about 10 mpg - fwiw. With that said, I don't drive enough to really worry about it.

[mcgsxr]

A different year and motor, but I get about 10mpg in town in my 69 with a 429.

Best I have seen it about 16mpg on the highway cruising a steady 60-70mph.

[jtschug]

When you select the driving gear, which one do you choose? The first dot or the second dot?

Also, what is the rear end ratio? Still 3.00:1, or is it higher?

Is there any black soot or smoke out of the tailpipe?

7 MPG is pretty low. 10 MPG (US) is more typical.

[Randy Mattson]

I agree with jtschug, my stock '65 390 does 10 - 12 in local traffic and 14 - 16 on the highway.
The 16 is using the 2 lane routes vs the interstate.
On a recent drive to KC, MO and back, it averaged 14.3 mpg...all interstate (70+ mph).
Randy Mattson

[BrianC]

Unless the engine isn't running right, MPG is the last thing you worry about on these cars, built in the day of $0.35/gallon gasoline.

[BillT]

Drive using the big dot, but the tranny often starts in second anyhow (see tranny issue below). And no black stuff out of the tail pipes. Also, the rear end is still 3:1 as far as I know, but a PO may have changed it.

I’ll soon be pulling the plugs to check them and the compression, and look at the timing and vacuum advance.

[jtschug]

Vacuum advance is a good place to check, it can hurt mileage if it isn't working right.

[jtschug]

Also, if you have the back of the car jacked up and trans in Neutral you can turn one wheel with your hands (with the other wheel stopped) count how many times the driveshaft turns each time the wheel turns if you want to confirm the rear end ratio