Gas Mileage

by Pdawgie Mon Mar 07, 2011 2:32 pm

I just put on a new 600 CFM carb a couple of weeks ago, and I'm only getting around 10 MPG with it around town (haven't been out of town yet with it), it seems like it should be getting better than that (maybe 13-15 around town). My engine is mostly stock with the only mod being an aluminum dual plane intake and the carb. I'm curious as to what you folks get for mileage on your cars?

by Limey SE Mon Mar 07, 2011 3:07 pm

new out of box or new to you ??

by The Dude Mon Mar 07, 2011 3:10 pm

1976 Malibu, stock 305/2bbl, TH350, 2.73 gears, still had AC, PS, PB, & a recent tune up - 100% stock. I was getting close to 21 mpg average on long trips. I never really paid much attention around town though.

What engine/trans/gears/car do you have? Also is it an Edelbrock/Carter/Weber or is your carb a Holley? IMHO, this can make a difference too.

by abajc3 Mon Mar 07, 2011 3:42 pm

Rago wrote:1976 Malibu, stock 305/2bbl, TH350, 2.73 gears, still had AC, PS, PB, & a recent tune up - 100% stock. I was getting close to 21 mpg average on long trips. I never really paid much attention around town though.

What engine/trans/gears/car do you have? Also is it an Edelbrock/Carter/Weber or is your carb a Holley? IMHO, this can make a difference too.

which one is better for mileage? i get 15 at best, that means 60mph on the highway. around town, its probably about 7 mpg.

by The Dude Mon Mar 07, 2011 4:17 pm

Well this is gonna start up another Rago vs the forum thread Laughing

, but the Weber design (Edelbrock/Carter) is a better suited carb for DD. Easier starting & better gas mileage in MOST people's experience. I still stand by my thoughts on power difference being negligible if not better with the Weber carbs, but some people disagree. Note that this is comparing the older Holley carbs. I have no experience with the Avenger series. They are supposed to be better built.

by pila Mon Mar 07, 2011 5:14 pm

There seems to be a glut of those Edel carbs these days. Maybe you will have to check the float level, which if it isn't correct, will sure affect fuel usage. And maybe some jet changes would help too......
Out-of-the-box carbs don't always match every engine.

by abajc3 Mon Mar 07, 2011 5:36 pm

im pretty sure that bad carb/intake combo is what is bringing my mileage down. but since im getting another carb and intake, im not even bothering to try to tune it up properly.

by Pdawgie Mon Mar 07, 2011 7:16 pm

The carb is brand new. It is a Summit street/strip carb wich is Holley made with Sunmmit logo, with the lift off top and no leak bowls on top of a performer manifold. I'm running a 350, turbo 350 and don't know what the butt gears are, haven't ran the numbers. Soon I will get it up on my lift and check the numbers. I will be putting a 700R4 in soon. I took off a 670 Avenger as I was having a sticky throttle issue. My 70 camaro has a 670 Avenger carb with a built 350/t350 and 3.08 gears and I get 18-19 out on the hwy with it.

by ant7377 Mon Mar 07, 2011 8:21 pm

Look at the plugs you might be too rich, need smaller jets. also the choke might be staying on too long and you might be rich there too .Try running it with no choke from cold. See if it helps.

by pila Mon Mar 07, 2011 8:28 pm

Good advice there from ant7377.

by IndyG3 Mon Mar 07, 2011 9:35 pm

In terms of gas mileage, my stock-ish 350 (leaky factory 2 barrel carb, only upgrades are a "high performance" HEI and new spark plug wires and plugs) can get about 18 mpg just about anywhere I go. I guess it could be a little better with a tune up on the carb, but that engine shouldn't be in much longer so I'm not too concerned about it.
I will say that although the leaky carb messes up the tuning a little, to its credit it does start and run like nobody's business.

by The Dude Tue Mar 08, 2011 10:24 am

Indy, wait till you start getting a bad wash-down in the cylinders & see how long that motor lasts. Mine lasted about a couple of weeks after I started smelling gas in the oil.

Pdawgie, a 350 with a 600cfm carb should definitely be getting better mileage than that. I was thinking you had a big block. Ant had some good suggestions so try them out & report back.

by IndyG3 Tue Mar 08, 2011 11:33 am

Rago wrote:Indy, wait till you start getting a bad wash-down in the cylinders & see how long that motor lasts. Mine lasted about a couple of weeks after I started smelling gas in the oil.

I don't drive it enough for that to be a real concern, and the motor's coming out early May. At this rate, it's just in there to keep the spot warm for the new engine.

by Pdawgie Tue Mar 08, 2011 1:13 pm

I put in new plugs when I put on the new carb, so I might need to drive her a bit to get a good reading. I'll take another look at the choke, but it seems to be working properly, after a minute or so of warm up, I tap the throttle and it comes right down to idle speed with no hesitation. I did adjust the air bleeds using an external tach.

It runs very smooth and I have no kind of fuel smell or loading up of any kind. I'll try running it with no choke when cold, and see what we get....

by bigredlaguna Tue Mar 08, 2011 9:26 pm

My opinion is that 11 mpg is within norms depending on driving conditions. Especially with the report of how the car runs.

My 06 hemi only gets 11 mpg. around town. For that matter, any V8 vehicle I've owned has gotten that around here.

by McCauley5983 Tue Mar 08, 2011 11:03 pm

what rearend do you have

by Pdawgie Wed Mar 09, 2011 3:04 pm

Don't know what the gears are... 10 bolt is all I know, by the feel of it, I believe they're somewhere around 3.08's, but haven't ran the numbers yet.

I'm going to try the choke thing and check my vacuum advance to make sure it's working properly and go from there.

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