Posted By: Lui Reyes Carb swap - Wed Mar 30 2022 06:43 PM
My daily driver is a '59 Apache that I recently put a 250 ci motor out of a '67 Chevy II in. I got close to 16 mpg on a 200 mile trip last Saturday. I am thinking of replacing the stock 1 barrel carb with a webber 32/36 progressive 2 barrel carb. Has anyone else done this and what kind of improvements did you get? I have read that you should get an increase in hp and mpg. I would like to get better mileage and would not be opposed to more power either.
Thanks a lot,
Posted By: Hotrod Lincoln Re: Carb swap - Thu Mar 31 2022 12:29 AM
Stovebolters either love Weber carbs, or they hate them. In my opinion, by the time you buy the Weber and manage to adapt it to the 250 intake, your time and money could be better spent on something that actually makes a difference. "Your mileage may vary"! The best way I've found to improve perfor,mance, and maybe get a little boost in MPG on a 250 is to install a nset of flat top pistons for a 307 Chevy V8. They're a drop-in fit, with no other modifications required, and you get almost a full ratio increase in compression.
Posted By: panic Re: Carb swap - Thu Mar 31 2022 02:27 AM
Your mileage is controlled by the high aero drag and weight of the truck, and its final gearing.
In the meanwhile, some comments on my site here:
HRL is right, more compression always helps.
Posted By: buoymaker Re: Carb swap - Thu Mar 31 2022 03:50 AM
Jon's website says 1967 Chevy II has a Rochester BV.
1967 GMC and Chevrolet trucks with 250, manual transmission, manual choke can come equipped with the Carter YF 4375S.
I would try the Carter.
If still not happy with MPG, read the Jeep forum response of the 32/36 on a Jeep 258. Good points and bad.
Has the engine been rebuilt since 1967? Worn rings and low compression could be possibilities.
If you 1959 Apache has a 3.90 rear axle I would try a 3 speed overdrive transmission assuming you currently have a standard transmission.
The optional 3100 rear axle ratios were 3.70 and 3.38. Do you know what you currently have?
You can try taller tires but it will throw off your speedometer reading a little.
Posted By: Otto Skorzeny Re: Carb swap - Thu Mar 31 2022 12:42 PM
16 mpg is pretty darn good for a 63 year old truck. How much of an improvement, if any, do you expect to gain with any modification? Remember that you're still pushing a heavy, non-aerodynamic brick down the road.

I've been using a 1956 Cadillac as a daily driver for 20 years. It gets about 11-12 mpg around town and 15-17 mpg on the highway. It's the price I'm willing to pay to drive a nice car.
Posted By: carbking Re: Carb swap - Thu Mar 31 2022 12:54 PM
If fuel economy is the ONLY consideration, very difficult to justify a major change.

16 MPG highway with a six cylinder, medium compression truck, is NOT bad mileage.

The Carter YF MIGHT give you 10 percent.

The Weber, IF you change intakes along with the carb, MIGHT give you 10 percent. If you use a 2-->1 adapter, you might LOSE 10 percent or more.

I do not know the percentage increase that higher compression would make (it will certainly make some), but doubt it would exceed 10 percent.

So do the math:

Lets say you drive this truck 5000 miles annually. At 16 MPG, you use 312 gallons.

Now increase your mileage by 10 percent to 17 and 1/2; and you still use 286 gallons.

So you didn't have to buy 26 gallons of fuel.


(1) how much to find the correct Carter YF, acquire a rebuilding kit (I can help with that wink ), and rebuild it?
(2) how much to find and acquire the Weber, rebuild it, and a manifold that will accept a two-barrel, manifold gaskets, air cleaner, etc.?
(3) how much to acquire new higher compression pistons, and rebuild the engine?

How many miles do you drive annually?

If the engine is needing to be rebuilt, then some planning when rebuilding the engine would be the time to make changes.

Posted By: carbking Re: Carb swap - Thu Mar 31 2022 01:01 PM
To continue the above thought, but in a different path:

Fixing a dragging brake, low pressure in one or more tires, REMOVING A BUG SCREEN ON THE HOOD, too low a temperature thermostat, etc. could easily get you the same increase in fuel economy at a fraction of the cost.

Posted By: Joe H Re: Carb swap - Thu Mar 31 2022 02:28 PM
On a different note, I installed a AIR/ FUEL ratio gauge on my truck and gained about 7 mpg with lots of tuning at highway speeds. Granted I am running dual Carter W-1's on a 250 engine. I found even though mine felt really good driving, it was on the rich side. By watching the gauge, I was able to change to the correct metering rods so the whole range of rpm was where I wanted it to be. The difference in mpg at 70 mph verses 60 mph is quite a step, and my '37 truck is a lot smaller then your '59. Last trip out on flat ground, 21 mpg @ 65 mph ( 250 mile round trip ) 3400 lbs, 3.08 gear ratio, 28" tall tire, 1:1 transmission ratio ( T350 automatic , A/C on. The price has gone up since I purchased it.
Posted By: Wrenchbender Ret. Re: Carb swap - Thu Mar 31 2022 03:40 PM
My 1 1/2 cents worth. 16 MPG on that truck is good mileage. If you are running the3:90 gears that generally comes with that truck my main improvement would be a set of
3:38 gears in the rear end or an o-drive trans like a T-5 with about 0.73 percent o-drive. That way you also have the advantage of faster speeds without the engine screaming, help me.
Posted By: 52Carl Re: Carb swap - Thu Mar 31 2022 10:56 PM
I agree with George. The best way to improve fuel mileage and performance with these trucks is the T-5. With the 3:90 rear ratio, or even a higher (numerically) ratio will work well.
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