What kind of mileage should a 72 Chevelle Malibu (307 auto, Rochester 2GCV carb, 38k Mileage) get? It started out around 14.8 loaded down with weight (2 passengers, 7 tires, roof top carrier and luggage) on the east coast and gradually dropped coming x-country. It definately was running rich so we leaned out the air/fuel and slowed the idle back down to 600; has lots of power so I assume the timing is set but was told it needed to be retarded for the altitude as well (anyone know the formula?). Seems to flood easily on colder days (choke?) I'm getting about 11 - 12 mpg now on mostly highway driving. Also noticed it emits white smoke and some kind of carbon for a few minutes after starting (more when cold, none when warm). This minimized after leaning the carb out so I assume it is caused by it still running rich. Thanks.

[This message has been edited by Anne (edited 12-28-98).]

Anne trucks when loaded don't get good milage either. Just joking.Roof top carrier there goes the aerodynamics. 307 2bl working pretty hard with that kind of load...FRED

Yea, thats what has me puzzled. Loaded going a solid 75 cross country it got 13 - 15 and now empty on 2 lane highways I'm only getting 12? This doesn't make any sense to me at all. Can the altitude make a difference as I've been told and how do I compensate for it? Like I said it has lots of pep, no dead spots when accelorating, but lousy mileage....

How many of those 38K parts are original? It sounds like a candidate for a full tune-up. I would say the dwell has changed and that's why leaning it out helped. Of course, the carb could do with a rebuild and perhaps the cap, rotor and wires are tired. A lot of low mileage cars show these kinds of problems when put back into service. Check the dwell and timing first... you should be getting better than 12mpg.

Anne, after visiting your web site I would take that mechanic to court and try go get your aunts money back. It should be easy to show a court that the parts that he says he replaced were indeed not replaced. I would imagine that most all the parts on the car are still original. I agree with Al a tuneup is in order. Even know it had one twice a year. Get the "dirtbag". Tom

Thanks. I had it tuned up by a very good mechanic we had used for about 15 years before it left the East Coast (and boy did it need it). That's probably why it ran great all the way from CT to NM.
Except for the work he did all of the parts were still original.(Even the sparkplugs and oil filter!!!)
I'm really thinking it is the dwell at this point, and the carb probably could use a rebuild. The gas that was in it was about 3 years old. I've run about 8 tanks through, but I'm sure that it could stand to be dumped and cleaned out.
Any more suggestions would still be welcome!
PS the dirtbag will get whats coming to him. I will have the receipts up in about a week.

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My 70 307 with same carb, newly rebuilt only squeezed out 14 mpg. I then added a HEI ignition, performer intake, 4bbl eddlebrok 650 carb. It responded great, but still only got 14 to 15 max. I have learned to live with regular fill ups. QS

Thats what I'm wondering if I'm going to have to do. Its not a dd so I could live with 14 if I can get it there. Found out more about the timing. Was told to advance it 6-8 degrees to adjust for altitude (7400ft). Does this sound reasonable? I'm still pretty new to this.

Being over 7 thousand feet you'll have to re gap your plugs and play with the carb to make it run right. Same thing happened to me in Yellowstone. Get a good mechanic to help you out with calibrating for that high up! Are you going to be up that high long?

Yea, I'll be here for about 2 more years. I live at 7400 but drive between that and about 6000 in 20 miles.
I just haven't found a mechanic who hasn't said to leave it at fac. specs. I didn't think of regaping the plugs though. I'll try that when I work on it this New Years.
What happens if I advance too much on the timing - will it just ping when I accelerate and then I can set it back until it stops or will this cause damage?

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[This message has been edited by Anne (edited 12-29-98).]

Pinging means that the fuel isn't being burned up completly, for what ever reason. In the long run, that will cause some problems. Try adding some fuel adative to the gas tank also, to help it stop pinging. Every little bit helps. Let us know how you make out Anne.

Burned through 2 more tanks of gas. Still getting low mileage but I am no longer getting lots of carbon and smoke. I think it was the old (3 year!) gas getting flushed out. My husband said this probably left a lot of varnish here and there - any good way to get rid of it?

anne, thats about right, there are tricks to get the milage even up to 25mpg but thats a long and painful story you can get a good 2 to 4 mpg gain "on tha cheap" but again a long story.email me if anybody wants my 2 cents on it! this crap thay call gas is the main or atleast part of the problem.....

Buy a Honda.

Had one already, thanks. Got totaled when an old Chevy bumped into it.


[This message has been edited by Anne (edited 01-17-99).]

I had a similar problem with my 68 moving from OH to NM (5500ft). My 68 has a 396 and has had some work done to it, but should still apply to your problem. I was getting about 9-10 mpg in OH. I changed from a 3.32 gear to a 3.90 just before I left. Here in Alb I get about 6-7, I don't think the gears make that much difference. You lose up to 20% of your hpr at this altitude, so your gas mileage is going to suffer. I ended up rejetting the carb and recurving the distributor. This took care of all my problems. That two barrel you have could be the biggest part of your problem. There is less oxygen at altitude to start with. The carb is choking it even more.

Had the original 307 and pg in my 68 with 37k and it got around 10-14 depending on how I drove it. You might want to try premium gas with octane boost, this *seemed* to help my 307 to an extent.

it posted this twice..why? I don't know..


[This message has been edited by Joe Y (edited 01-19-99).]

Can't thinnk of any reason why you shouldn't get 17-18mpg's at low altitide.
I had the following vehicles and the gas milage was as follows at cruising speed (60-65).
1966 chevy caprice (283 2bbl) = 18-19 mpg
1972 olds cutlass (350 2 bbl) - 16-17 mpg
1968 Chevy Nova (307 2 bbl) - 18 mpg
1974 Chevelle (230 1bbl) - 19 mpg's
1976 Chevy F150 (454 4BBl) pulling trailer - about 4mpgs.