Horrible gas mileage in my N/A GLH

[onesimo58]

After doing the math on a whole tank of gas I'm getting about 12 mpg. That is horrible. My gt mustang gets better gas mileage than that. I'm not too familiar with the 2 barrel holley carburetor, I would like to know how to adjust the air/fuel mixture to try and get better gas mileage. Exploded diagrams of the carb or even pics of where the parts are located on the carb would be very appreciated.
Thanks

[Shelby-Rampage]

Others may chime in, but I ran into the exact same thing on my rampage years ago (I got about 13mpg with an auto). I changed everything to get better mileage (tune up, jets, etc.) all to no avail. Then the last thing was the carb itself. I went to a weber carb and not only did my mileage more than double, but it gained power and ran soooo much better. Best money I ever spent. Later, I went to a five speed after that from the auto...what a differance those 2 things made, high 30's on the highway now.

[roachjuice]

dam!

[vntned]

The carb is whats ruining your mileage. My buddys '83.5 SC went from mid 30smpg to about 20 now. His carb is junk!

[dirtyglhturbo]

look at them spark plugs. are they blackend like your chicken at dinner, or are ya running clean. if your not running rich, all the spark plugs and tune up parts in the world aren't gonna help you. that might be the way it is.. my famous quote " a carburetor is as efficent as a toilet bowl"

[DaytonaTurbo87]

Carbs can get good mileage, but they do wear. Sounds like yous is leaking fuel inside the carb. That's not going to be a matter of jetting, it's just the carb's way of telling you it needs a rebuild. And by a rebuild it means replacement with a small webber. A suitable replacement can be purchased off ebay for usually $30-50. But first I guess you could just check to see that your choke is opening all the way. If choke is working properly, and mileage is still crap, I would just replace with a webber. Better power and better mileage.

[Wizard]

Hand raised. Had Holley (rebuilt it 3x), now weber and watching the MPG rise with each tweak. Was 10-13, now 17-18mpg In caravan with old 2.2 with 3 speed.

Go WEBER!! 32/36 DFEV is your best fit need to take a linkage lever off the old carb and slightly modified. Start grinding the mushroomed shaft that riveted that linkage to the throttle shaft, extract it intact and dermel cut off most of them off except the fast idle linkage nubbin and use small slim diamond file to file double D flats wider to fit weber's shaft (do it accurately) and to "reposition" throttle linkage more correctly.

Cheers, Wizard

[onesimo58]

Thank you guys for your input. It looks like I'm going to go with a weber soon. I've got a pair of 40mm DCOE's lying around and also an auto an manual choke 32/36 DGV's. I'm a big fan of weber, just wanted to make that my last resort. I did check the choke on the holley and it is opening all the way when warm. I replaced the plugs and air filter about 200 miles ago. I pulled one of the new plugs out yesterday and it was nice and black. I also check to see if my O2 sensor was working properly(it was) I then went driving around with the multimeter still connected. cruising down the high way at about 3000rpm and the O2 sensor was putting out between 6 and 9 millivolts, if I'm not mistaken stoichiometric is about 4.5 millivolts. I'm not sure if I'll put on another carb. I recently got a turbo motor that I'm going to put in it while I'm rebuilding the HO motor.