Gas hog

My gas mileage has noticeably gone down recently. I have checked my whole fuel system for leaks and havent found any. In the last 13 days I have spent $120 on gas and I hardly drive. I'm not sure if this could be correlated with my fuel economy but when coming to a stop or making a turn my rpms drop almost to the point that my engine dies. I am usually pretty quick to figure out these kind of problems but I am at a loss for this one. Hope one of you guys might know the answer, thank you.

Sounds your carb could use some attention. What's your whole setup and what were you getting for mileage before/after?

Put a cummins diesel in it....

TotalyHucked said:

Sounds your carb could use some attention. What's your whole setup and what were you getting for mileage before/after?

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I have a 615cfm Edelbroken carb that's only a few months old, its on a 1st gen 4 bolt main 350 paired with an sm465 transmission. I have 31" tires and no lift. I'm not sure what mileage I was getting before but i know my gas gauge wasn't going down as fast as it has been recently. I'll adjust my carb right now and post an update in a few hours.

Or it could be the gauge failing. Without knowing your actual mileage, it's impossible to know if you have an actual issue or not

Make sure your vacuum advance can hasn't ruptured,and is connected to manifold vacuum.

Maybe someone siphoned some fuel out. You never know.

SamHam said:

I have a 615cfm Edelbroken carb that's only a few months old, its on a 1st gen 4 bolt main 350 paired with an sm465 transmission. I have 31" tires and no lift. I'm not sure what mileage I was getting before but i know my gas gauge wasn't going down as fast as it has been recently. I'll adjust my carb right now and post an update in a few hours.

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Weather got cold up here recently and they probably switched to winter blend now, which will show a few MPG lower. Your stumbling at idle makes me think vacuum leak though. Start it up and spray some carb cleaner all around the intake manifold and see if you notice an RPM change. What part of Oregon are you in?

SamHam said:

My gas mileage has noticeably gone down recently. I have checked my whole fuel system for leaks and havent found any. In the last 13 days I have spent $120 on gas and I hardly drive. I'm not sure if this could be correlated with my fuel economy but when coming to a stop or making a turn my rpms drop almost to the point that my engine dies. I am usually pretty quick to figure out these kind of problems but I am at a loss for this one. Hope one of you guys might know the answer, thank you.

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Have you actually calculated your mileage? If so, what is it now, compared to before? What type of driving do you do? Have you been letting it warm up before you drive it?

Does it stink like fuel? Is it running ok besides the idle issue?

I live in western Oregon so its about 40-50 most days right now. I haven't calculated the actual mileage yet but I will next time I fill up, which is probably soon lol. I will try the starter fluid trick and check all my vacuum lines. I'm suspecting its just bad carb tuning right now.

Didn't read all the replies but your area could be starting the use of winter fuel which will hurt MPGs.

Winter blend gas usually is only a couple % less efficient. Hardly noticeable. Certainly not grossly worse.
However $120 in 13 days “ not driving much” doesn’t even begin to calculate to fuel mileage and even if it did, no basis for comparison.
Idk if the wet side of the Cascades runs winter gas or not.

All the suggestions above are good places to start.
And it may just be the Eddy carb. I have 2 now one in a big block other on a 350. Haven’t spent the time to try to tune them, but a 750 Eddy on a Gen VI 454 pushing the worlds heaviest 35s with 4.10s = 6-7mpg. And an assuming smaller carb idk what model or cfm on a poochy new 350 1/2 ton with 3.54s is about 11-12mpg.
For reference.
The big one may be running a bit rich, not horribly though. The little one burns clean at the tailpipes.

I'm fixin to replace the edelbrock carb on the 84 305 to a quadrajet like I have on the 82 454 because it runs great with it. I've had 2 edelbrock carbs and both have sucked for me. Quadrajet has never had any problems on my trucks.

I'll be using national carburetor in Florida because they tune and test them. They're proud of them for 350 bucks with 50 bucks for core charge so 400 total, But I bought the one on the 454 from them and slapped it on with no issues. Fired right up and that was about 6 years ago. Also I don't drive it much and it still runs great after sitting a few weeks.

If the 84 sites a little bit it won't fire up unless I spray ether in it and then have to keep my foot in it until it warms up. You can get a $200 quadrajet off Amazon but a lot of people say they're not tuned and have had to return them a couple of times and still don't get a good one. So I'll pay a little more money and get one I know will work.

I'm in Salem and am still running a 350 with 9:1 compression and a summit K1102 cam. I've got the factory quadrajet on it and it has been dialed in with an AFR meter and is right on. I get ~8MPG towing and around 10-11MPG just driving around. I'm on 35's with a TH400/NP205 combo, so I get all the drivetrain losses. I have a 31 Gallon fuel tank and fuel is 3.15/gal right now. So, best case, I can go 311 miles on a tank of gas and it will take ~$100 to fill it up afterwards. It gets infinitely worse if you are warming it up for any amount of time on the choke.