My 68 is really giving me fits. Yes I do tend to gun it every now and again. But this is getting silly! Yesterday I had between 1.5 and 2 gallons of gas, and I drove roughly ten miles. Well, needless to say I ran out of gas.
What could be causing such horrible milage? I mean, do the secondaries on an 1850/4160 really suck down gas that much? It just sometimes seems like my car gets such horrible gas mileage driving around town that something must be wrong. Sometimes it seems like driving a couple of miles takes a half gallon. Is something wrong? Or can you guys burn a half gallon gunning it on the freeway on ramp to 70?

yes, there is something wrong!

Is it very rich??

How do you know you had 1.5 - 2 gallons of gas? Have you ever actually averaged your mileage? If not you should so you know exactly where you are. Your cam is not that wild so I don't see it wasting gas out the tailpipe. As Drag said are you running really rich?

When you start opening up the secondaries it will tend to drink more gas. Rev'ing and ideling a lot will burn up more gas than you would think as well.

Try to get a baseline on you mileage (while driving mildly) and go from there.

OH, If you are actually getting less than 8mpg something has to be wrong/out of tune.

And remember, with 1.5 or 2 gallons, the fuel pickup isn't going to pick up every last ounce. You probably still have a gallon in there. You actually may be getting 10MPG.

How do your plugs look?

I drove to reno (hot aug nights) and got 24mpg on the first half of the trip there (383 holley 780 overdrive 3.73:1 rear). That was following my buddy with 4:10's at 60mph. I drove around town and cruised every night for 3 nights (can you say 5mph for several hrs at a time) and got a wopping 5-6mpg... A lot has to do with how you play... graemlins/beers.gif

Maybe it is running rich. I can smell gas in the exhaust. I am sure it isn't buring it all. Maybe a jet change is in order. I will check it out when I rebuild my carb.

I think Royce hit on something there. If it was bone dry to start with, you probably need a half gallon just to prime the lines, pump, and float bowls.

Then lead-footing it around town will suck A LOT of gas -- just for reference --- When I race I leave my house with a full tank. Drive 65 miles to the track and use a little over 1/4 tank getting there. I use roughly another 1/4 tank making usually about 6 passes (thats only 3 or 4 miles). Then drive 65 miles home and arrive with less than 1/4 tank.

I wouldn't worry about your gas mileage unless the engine isn't running right (sooty plugs, bad idle, lack of power, etc)

you can smell gas at idle? Maybe a powervalve went bad?

its hard to diagnose problems over the internet, but i would venture a guess that something is out of tune.

You can approximate your rear-end ... It is the ratio of # of drive shaft rotations vs 1 complete rotation of the rear tires .. Also, tire height will make a difference ... still, bottom line is a fresh tune-up is the best starting point and make sure air intake is not partially clogged and air filter is excessively dirty ...