Carburetor jetting for 1951 vs 1952 carburetors?

[Caddy Wizard]

Here is a question for all of you carburetor experts!

My recently acquired 1949 Fleetwood has a 1952 motor installed in it, which as many of you know, is a higher output motor than the original 1949 motor (but both are 331s, of course).  The 1952 motor has a 1952 Carter 4-barrel carburetor on it, which is correct for the 1952 motor, but looks like crap in the 1949 engine bay (especially the air cleaner).  Plus, the first year (1952) 4-barrel carburetors are more troublesome than the highly developed Carter WCD 2-barrel carbs of 1949-1951.  So I have acquired a complete 1951 setup (manifold, carb, and air cleaner), which looks very correct in the 1949 engine bay (visual differences between the 1949 and 1951 2-barrel set ups are minimal).  I've restored and rebuilt the carburetor and am ready to install.

The question is about the main jetting.  The 1952 Carter 4 barrel carburetor has main jets that are 0.0935", while the 1951 Carter WCD 2-barrel has main jets that are 0.089".  So there is a 5% difference in main jet size.  I am a little concerned that the 1951 carburetor will tend to run a little lean at cruising speeds (lean running at cruising speeds is not a good thing).  The 1952 engine is a higher HP motor than the 1951, so the carbs are jetted differently.  Maybe I shouldn't worry about it.  Maybe I should use slightly larger main jets in the WCD.

Thoughts?

[wheikkila]

I have done a lot of carb repairs and adjustments. I would get a couple different size jets. I would pull the plugs and make sure they are clean. Then I would start with the factory setting. I would drive the car a little and see how it drives and check my plugs. To set up the carb. You have to start somewhere. Factory is as good as any.
               Thanks Wayne   

[Caddy Wizard]

I have done a lot of carb repairs and adjustments. I would get a couple different size jets. I would pull the plugs and make sure they are clean. Then I would start with the factory setting. I would drive the car a little and see how it drives and check my plugs. To set up the carb. You have to start somewhere. Factory is as good as any.
               Thanks Wayne   

That was sort of my plan.  The difference between the two main jets is only 5%.  So it is going to be pretty close.  Car is in excellent tune.  I figure to run it with the 51 carb at a cruising speed and shut it off and let it coast to a stop.  Then pull some plugs on the side of the road and look to see if they look to be running too lean.

You and I are thinking the same.

I'm wondering if the venturis are the same sizes or different.  It might be that the 51 venturis in combination with the 51 main jets will yield an air-fuel mixture that is essentially the same as the 52 venturi-main jet combination...

[wheikkila]

I would think it should be fine. Like you said it is only 5%. You should be able to go up in size slightly without a problem. If you were building a race motor that would be different.
             Thanks Wayne   

[fishnjim]

Not something I carry around but may have the info. 
Do I get this right, you want to know(specs) what the primary is on the 4bbl vs the WCD 2 bbl?
Would help to verify the '51 and '52 carb numbers, so we're on the same page.   Just cause they came from there doesn't mean they might not have been changed over time.

I don't think the WCD will be anywhere close to the 4bbl in overall cfm.  Something like ~300 vs ~450?   But I'll check.   

If the cfm is different, that might explain the 5%.  But other things probably changed in the higher output motor too. 
On the surface, I don't think there's much to worry about as is but pays to check.  It'll have to be re-tuned for the 2bbl.
You can always put the exhaust analyzer on it too and check the rich/lean through all the rpm ranges.   Someone put an O2 sensor too.

[wrench]

Is this single or dual exhaust?

[Caddy Wizard]

Is this single or dual exhaust?

Single exhaust.

[Caddy Wizard]

Not something I carry around but may have the info. 
Do I get this right, you want to know(specs) what the primary is on the 4bbl vs the WCD 2 bbl?

Would help to verify the '51 and '52 carb numbers, so we're on the same page.   Just cause they came from there doesn't mean they might not have been changed over time.

The 51 is a Carter WCD 845S -- definitely a 51 Cadillac carburetor. 

I pulled the main jet specs from the Shop Manuals for these two years.  I need to look again to see if they mention the sizes of the venturis.

[Omarine]

So i also have the carter 2 bbl on my 52 engine.  In an effort to see how it was burning, i spent the $200 on the auto meter air fuel mixture digital gauge.

This was around the time in September here in Florida when i shoved an air paper element into the oil bath filter.

Since the car is still 6 volts, i borrowed the battery from my other car and placed it in the floor to power the unit. Welded the exhaust bung and started toying with it.

I ran super rich at idle, then leaned out on the road. I wanted to start playing with jets, but was advised to check the float setting.

Turned out it was way too high causing rich mix at idle. Solved that issue.

Then started  messing with air cleaner. After some trial and error, the mixture evened out on the road only after reinstalling the oil bath filter correctly without the paper element.

So in the end, no jetting needed. Did this in September here in Florida when it was very hot out still.

Very happy with the gauge...it was temporary so it's back in the box till next time.

Cheers
Oscar

[wheikkila]

I'm not surprised. A lot went into these factory setting. That is why I start with the factory setting. I don't need to reinvent the wheel.
                         Thanks Wayne 

[Caddy Wizard]

So i also have the carter 2 bbl on my 52 engine.  ...

So in the end, no jetting needed.

Cheers
Oscar

Thanks for sharing.  I rebuilt the carb very carefully and expect that I have the float set correctly.  From your experience doing exactly what I am doing (putting a 51 carb on a 52 engine), I am guessing that I will be fine without replacing the 51 carb main jets with larger ones.  But I will still run it at speed and check the plugs just to be sure.  Thanks.

[wheikkila]

Be sure to let us know how it turns out.
Thanks Wayne