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Carter WDO carb advice for improving fuel economy


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I would like to improve the fuel economy in my 1939 LaSalle. It has a Carter WDO 423-S carb that I rebuilt last year but didn’t have the template gauge to set the metering rod height so I used suggestions in several pieces of literature I found on line. 


I have 500 miles on a freshly rebuilt engine.  Although it runs and drives great, I’m only getting about 9 mpg driving 55-60 mph. The exhaust pipe is a bit sooty. So my question for anyone who has played around with these carbs is:

 

Can I just adjust my metering rods to be lower? I think I do that by loosening the screw and rotating the metering rod arm so both rods sit lower at the same throttle setting and re-tighten the screw. I don’t think the will affect the anti-percolator settings. It’s been a year so I don’t quite recall the details and hate to mess it up too much since it runs great but just too rich.  It seems I could just may small changes and look for economy improvements through trial and error. I'll know I went too lean if it starts running poorly. Anyone try doing this before on another WDO? Thanks for any help.
Scott
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As far as the carburetor is concerned:

 

Find the gauge, and set the carburetor to standard setting; then, and only then, you have a repeatable baseline. Until then, you are guessing!

 

The white tailpipe that was once a sign of a well-tuned engine...............................was lead residue!

 

The tailpipes on my OT newer factory fi vehicles are brown/black in color.

 

Fuel economy is definitely NOT all carburetor. Here is an article I did a few years ago:

 

http://www.thecarburetorshop.com/Troubleshooting.htm#Fueleconomy

 

Others may chime in as to what one should expect for fuel economy on a 1939 LaSalle

 

Jon.

 

 

Edited by carbking (see edit history)
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Thanks Jon.  I think I have all the other fuel economy points covered....brakes properly adjusted, new Diamondback Radials set to 42 psi (seems to be the sweet spot), timing correct, running non-ethanol fuel, etc.  I would expect something between 12-15 mpg.

 

So maybe my new question is - does someone have a gauge they can loan me?

 

 

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Once you get the carb squared away, install a vacuum gauge where you can easily see it while driving. Tee-ed into a vacuum wiper line above the windshield is a good spot for early cars. It's not just a tool for trouble shooting and adjusting. Used while driving, it's actually a poorman's "load meter" showing how much load (which is gas being used) you are putting on the engine.

 

Then learn to drive by keeping the needle reading as high as possible under all driving conditions while still maintaining the desired speed. The lower you push the needle while accelerating, the more gas you are wasting. 

 

You'll be surprised how much better an "educated gas pedal foot" can do on gas mileage.  After a few tank fulls, the savings will pay for the gauge !  ;)

 

Paul

Edited by PFitz (see edit history)
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8 hours ago, Stude Light said:

I have 500 miles on a freshly rebuilt engine.

I would not think 500 miles as being broken in.  My 1953 Buick took nearly 5,000 miles before the performance and mileage improved to what I thought was normal.  It was almost 3,000 miles before the mileage started to improve from 9-10 mpg, then there was an improvement at almost every fill-up.

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1 hour ago, Tinindian said:

I would not think 500 miles as being broken in.  My 1953 Buick took nearly 5,000 miles before the performance and mileage improved to what I thought was normal.  It was almost 3,000 miles before the mileage started to improve from 9-10 mpg, then there was an improvement at almost every fill-up.

With modern oils it can be a painfully long time breaking in a motor. I've torn down a motor at 1500 miles  and the engine machine shop's cross hatch honing marks in the cylinders looked like they did when I first assembled it.  Total Seal recommends a special break-in abrasive paste to coat the cylinder walls to speed up the break in of their piston rings with modern oils. And they recommend not oiling the pistons, rings, or cylinder walls during assembly.  Just wipe a very thin layer of the paste on the cylinder walls and then install the pistons dry. I cringed the first time I followed their directions, but it did work to speed up break in and not have an engine that burns oil. 

 

Paul

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Can you manually retard the ignition timing from the dash?

The first place I'd start would be to advance the timing, mybe significantly. which would require you are able to retard the timing for starting.

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15 hours ago, Tinindian said:

I would not think 500 miles as being broken in.  My 1953 Buick took nearly 5,000 miles before the performance and mileage improved to what I thought was normal.  It was almost 3,000 miles before the mileage started to improve from 9-10 mpg, then there was an improvement at almost every fill-up.

Good point

9 hours ago, cahartley said:

Can you manually retard the ignition timing from the dash?

The first place I'd start would be to advance the timing, mybe significantly. which would require you are able to retard the timing for starting.

No way to set timing from inside.  It has mechanical advance but no vacuum advance.  I was thinking of advancing a few degrees, especially since the lower compression engine (6.25:1) wasn't designed for 87-89 octane fuels. It's easy to change.

 

Thanks everyone, for all the advice.

Scott

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  • 2 weeks later...
On 7/14/2020 at 8:53 PM, PFitz said:

With modern oils it can be a painfully long time breaking in a motor. I've torn down a motor at 1500 miles  and the engine machine shop's cross hatch honing marks in the cylinders looked like they did when I first assembled it.  

 

Paul

 

I put a set of pistons & rings in my '07 Chevy Silverado for oil consumption at about 225,000 miles. (piston issue & cracked head due to a design & manufacturing flaw).  At that miles because of the new low tension rings, I could still see the cross hatch marks on the cylinder walls and I had no ridge at the top of the cylinder. 

 

GM recommends that you DO NOT hone the cylinders prior to putting in the new pistons & rings on this vehicle along with new heads.  Just stuff the new pistons & rings in the holes.

 

I did not hone the cylinders and my oil consumption went up to about 6,000 miles/ quart.

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Do as Carbking says. Set your metering rods to factory. You will also need to raise you float height to nearly an 1/8th Over factory settings as modern fuel has a way less Specific Gravity. ( you’ll be running rich at factory settings. ) . Then use a vacuum gauge to set you air screw to the maximum vacuum you can get. The adjust your timing to get maximum vacuum again. Then go back and do the air screw on more time. Then do the timing one last time to get maximum vacuum. Once this is achieved, retard timing by one column. 
a quality Vacuum gauge with a big dial is best. This method is by far the best way to tune those Carbs and your timing. Ask any Hudson guy. 
good luck. 

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11 hours ago, paulrhd29nz said:

Do as Carbking says. Set your metering rods to factory. You will also need to raise you float height to nearly an 1/8th Over factory settings as modern fuel has a way less Specific Gravity. ( you’ll be running rich at factory settings. ) . Then use a vacuum gauge to set you air screw to the maximum vacuum you can get. The adjust your timing to get maximum vacuum again. Then go back and do the air screw on more time. Then do the timing one last time to get maximum vacuum. Once this is achieved, retard timing by one column. 
a quality Vacuum gauge with a big dial is best. This method is by far the best way to tune those Carbs and your timing. Ask any Hudson guy. 
good luck. 

I'm currently searching for the correct metering rod gauge or maybe make one.  I totally agree on utilizing a vacuum gauge, they can be a very good tool that are often ignored these days.  Thanks for the advice.

 

As far as specific gravity....that has really not changed.  Todays gasoline has a specific gravity around 0.74 (0.71-0.77 depending on the exact gasoline and manufacturer).  Data that I have shows in 1939 summer gasoline available in the Detroit area ranged in specific gravity from 0.72 - 0.75 as sampled from Gulf, Hi-Speed, Shell, Standard, Sinclair, Texas, White Star (Socony-Vacuum), Cities Service and Sun. Regular gas averaged 71.5 octane , Ethyl averaged 78 octane and Third averaged 65.5 octane. Prices were a bit cheaper though as Third was 13.1 cents/gallon, Regular was 15.7 cents/gallon and Ethyl was 18.2 cents/gallon.

Scott

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9 hours ago, Stude Light said:

 Prices were a bit cheaper though as Third was 13.1 cents/gallon, Regular was 15.7 cents/gallon and Ethyl was 18.2 cents/gallon.

Scott

 

  Think so?     .15 in 1939 equates to $2.78 today.        Close to the same.

 

  Ben

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