Bronco MPG
Posting Guru
Joined: Jan 2005
Posts: 1,749
Likes: 0
another disappointing tank for me.. but when I last filled up, I had 12gallons in the tank with an 1/8th? It's not the gas mileage I'm mad at.. it's just that, it was $1.80 a gallon when I bought the truck, grr..
it's alright though, my second car is about to be a hybrid.. I'm also a vegetarian.. so yeah, 40mpg Fusion, 10mpg Bronco, still averages out better than most cars on the road.. right? :P
it's alright though, my second car is about to be a hybrid.. I'm also a vegetarian.. so yeah, 40mpg Fusion, 10mpg Bronco, still averages out better than most cars on the road.. right? :P
Moderator
Joined: Dec 2007
Posts: 7,987
Likes: 104
From: Boise, Idaho
I have a 600cfm on my 300 I6!
A bigger carburetor doesn't necessarily use more fuel, that's a common misconception.
What a carb that's too big does is require too much air flow from the engine to get a good, strong fuel signal. This can create weak acceleration, sluggish performance, etc.
When looking for a carb, you want the smallest size you can use without starving your engine when it needs it most. The smaller the carb, the better the throttle response. However, the smaller the carb, the less top end you have because it can't breath.
Fuel mileage is all in how you tune the carb.
For reference:
I averaged 7 - 10mpg around town with my 190cfm 1bbl. I averaged 10 - 12mpg around town with my Holley 390cfm 4bbl. Now, I'm averaging 12 - 14mpg around town with my Holley 600cfm.
A bigger carburetor doesn't necessarily use more fuel, that's a common misconception.
What a carb that's too big does is require too much air flow from the engine to get a good, strong fuel signal. This can create weak acceleration, sluggish performance, etc.
When looking for a carb, you want the smallest size you can use without starving your engine when it needs it most. The smaller the carb, the better the throttle response. However, the smaller the carb, the less top end you have because it can't breath.
Fuel mileage is all in how you tune the carb.
For reference:
I averaged 7 - 10mpg around town with my 190cfm 1bbl. I averaged 10 - 12mpg around town with my Holley 390cfm 4bbl. Now, I'm averaging 12 - 14mpg around town with my Holley 600cfm.
Post Fiend
Joined: Nov 2011
Posts: 8,908
Likes: 1
From: Algona, Washington
Oh ok that makes sense, this is what i have now
The choke needs fixing and a new choke thermo, i don't really know if that is the correct wire for it but when i got it the thermo was just sitting on there and the wire was tucked into the harness on the firewall. I put a volt meter on it and i think it got like 9 volts or something, i need to also put the retainer ring on it so it stays on the carb.
I am actually planning to rebuild it so that i can have a rebuilt one and i have the experience to rebuild one.
The choke needs fixing and a new choke thermo, i don't really know if that is the correct wire for it but when i got it the thermo was just sitting on there and the wire was tucked into the harness on the firewall. I put a volt meter on it and i think it got like 9 volts or something, i need to also put the retainer ring on it so it stays on the carb.
I am actually planning to rebuild it so that i can have a rebuilt one and i have the experience to rebuild one.
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Posting Guru
Joined: Jan 2005
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Looks like my 2100.. man, I loved that carb. Thing is like 500CFM for a 2bbl, which is insanely good. They're reliable, easy to rebuild and fun to work on.
Honestly, it looks like your accelerator pump doesn't have any options for adjustment? Mine had a few holes where I could adjust it, so maybe mine wasn't stock?
Also, if your choke doesn't open up 100% when warm, then you're burning gas when you shouldn't be. You just want to show some voltage to the choke, it's electric assist and it just needs a steady voltage to keep it warm (and open) when warmed up. Your choke opens up fully when warm, right/ The center plate, it should be 90degrees after a few minutes
Honestly, it looks like your accelerator pump doesn't have any options for adjustment? Mine had a few holes where I could adjust it, so maybe mine wasn't stock?
Also, if your choke doesn't open up 100% when warm, then you're burning gas when you shouldn't be. You just want to show some voltage to the choke, it's electric assist and it just needs a steady voltage to keep it warm (and open) when warmed up. Your choke opens up fully when warm, right/ The center plate, it should be 90degrees after a few minutes
Post Fiend
Joined: Nov 2011
Posts: 8,908
Likes: 1
From: Algona, Washington
Ya i think the electric assist is shot. I think they are pretty cheap so maybe tomorrow i will take a trip up to Napa and see about getting one. I know replacing the one on my 82 mustangs 1 bbl helped a bit. A question though, what do you think it should be set at? There is lines on the top and should it be in the center?
Moderator
Joined: Dec 2007
Posts: 7,987
Likes: 104
From: Boise, Idaho
This is why 4bbls can get better gas mileage than 2bbls.
If you had a 500cfm 4bbl, you'd have the same fuel flow through the carb at WOT, so you wouldn't have any performance downsides, but when you let off the gas and are just cruising, half of it closes, and you're pulling from, basically, a 250cfm 2bbl. Gives you better throttle response, and the throttle blades have to open further to give you your fuel needs so you don't have as much pumping losses.
If you had a 500cfm 4bbl, you'd have the same fuel flow through the carb at WOT, so you wouldn't have any performance downsides, but when you let off the gas and are just cruising, half of it closes, and you're pulling from, basically, a 250cfm 2bbl. Gives you better throttle response, and the throttle blades have to open further to give you your fuel needs so you don't have as much pumping losses.
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