Technical Carb Gurus Needed - Carter WCFB Leaning Out at Part Throttle

I think you might be right about the small jetting.

I thought this issue was only during the transition circuit because it didn't happen if I revved it up really fast, but yesterday (did this in my driveway) I slowly revved it up to experience this issue, quickly pushed past it so it wouldn't die, and then kept the rpm raised after that. When I held the RPM up high, it sounded like it was lean and pretty unhappy. It wasn't lean enough to die, but it didn't sound smooth like she does coming off idle.

I'm starting to think the whole main circuit is lean. Maybe the lean out issue I'm having is when the idle transitions to a lean main circuit. If I push past that transition, it then runs on a lean main circuit. The only way I can avoid all these issues I'm experiencing is by having the choke completely on.

I don't think it's a fuel supply problem because it still happens if I turn my transfer pump on. I had the carb apart the other day and I don't think I'd feel comfortable raising the floats anymore. I wonder if someone swapped metering rods and jets trying to fix another issue.

What do you all think?

-Chris

 

Okay, so I kept wondering if maybe I swapped the main jets when I rebuilt the carb. I opened it back up to find the bigger of the two sets in the front (Primary), and the smaller in the rear. The weird thing is, the rear jets with the smaller openings have a bigger number on 'em. They read 120 on the top, and 175 on the bottom.

The front jets with the bigger openings read 120 on the top, and 165 on the bottom.

Also, the rods read 75-1163

Is this normal or is something weird goin' on?

-Chris

 

I doubt that you switched them but aside from the labor it's a quick and easy thing to swap them and give it a try. I know I would.

 

Well, after doing some homework, the jet numbers look right. I don't know if they're correct for my application or not, but I found a conversion chart.

The Primary mains that read 120-165 are .086 in size.

The Secondary mains that read 120-175 are .073 in size.

So, the smaller number is the bigger of the two jets.

Does anyone here know if these jets are correct for my application?

-Chris

https://www.carburetor-blog.com/knowledge-base/carter-jet-conversion/

 

Update: The factory parts manual lists what main jets and rods should be in that carb from the factory.

The manual lists a .086 primary main jet. It doesn't list the pn, just the size. So, referring to that Carter jet conversion chart I linked earlier, it has the correct jet (assuming it hasn't been drilled out).

The manual does list the actual pn for the metering rods. It lists the factory metering rod as 75-824. My carb's rods are 75-1163.

I found a Packard TSB document that confirms the standard rod pn as 75-824. It also lists two other rods to lean this circuit out if need be. It lists "One Size Lean" as 75-892, and "Two Sizes Lean" as 75-893

https://packardinfo.com/xoops/html/downloads/SC/SC-VOL27NO4.pdfhttps://packardinfo.com/xoops/html/downloads/SC/SC-VOL27NO4.pdf

Based on those numbers, it would appear that the higher the number, the leaner (or physically bigger) the rod is. If this is the case, my carb's metering rods are WAY lean.

What do ya guys think? Am I on to something?

-Chris

 

Carter part numbers, in this time period, are part numbers. Not until the mid-1960's did Carter codify the jets with the actual sizes.

Metering rod part numbers are.......................part numbers.

But your rods are just plain wrong, and exceptionally lean. IF your carburetor IS from a 1953 Packard. I may have missed it, but did not see where you posted the tag number.

Jon.

 

If your carb has the original tag post a photo so Jon can help you with the correct internal parts. It sounds like you just need to install the jets as indicated and look for the proper metering rods. You’ve done some excellent research so far. Putting the carburetor back to factory stock, a new set of spark plugs and setting the points and timing should be the baseline you need. If it runs fine, you’re done. If it needs improvement you at least have a solid baseline to work from.
This is a good thread, lots of back and forth sharing of information. There’s always something to be learned.

 

A bit of information about Carter calibration, and part numbers. I have posted this before (several times ) but some of you dudes are like the mechanics of 75 years ago The carburetor companies used to issue service bulletins to the car manufacturers, the car manufacturers copied them and forwarded them to the dealerships, the service manager then passed them out to the "mechanics". The "mechanics" repurposed the bulletins (well, they were printed on fiber (soft) paper, and not as slick as the Sears & Sawbuck catalog pages)

Carter started codifying parts by type using a prefix representing the type (a 120 prefix meant a certain type of main metering jet, a 75 was used for certain metering rods) of part about 1922.

Until the mid-1960's, one got no information as to calibration by looking at the part numbers. Part number 120-1 through 120-349 were simply part numbers.

Beginning with part number 120-350, the number was the size in thousanths. This again was codified.

FOR standard height jets, a 3nn number would be 0.0nn in size. Thus 120-350 would be a standard height jet 0.050 inch diameter. Since Carter produced jets greater than 0.100, changing the 3 to a 4 would indicated a jet diameter greater than 0.100. Thus 120-407 would be a standard height jet of 0.107 inch diameter.

For high step jets, 3's became 4's, and 4's became 5's. Thus 120-498 would be a high step jet of 0.098 inch. 120-507 would be a high step jet of 0.107 inch diameter. Most folks think of the high step jets being used on the AVS carbs (which they were), but Chrysler used high step jets in some AFB's.

There was another weird jet used for some California AFB carburetors that was significantly taller. For these jets, the 3's and 4's were replaced by 7's and 8's. Thus 120-792 was a weird jet of diameter 0.092.

The metering rods are a little more difficult to understand. GENERALLY, the number stamped on a metering rod (prefix 75) or step-up rod (prefix 16) would simply be the next sequential number when a new rod profile was needed. This is not always true, as some of the newer rods (late 1960's and newer) have the number the engineers assigned stamped on the rod, but marketing assigned a different (sales) part number. The numbers on the rods have not had any intrinsic meaning as to calibration size.

Considering jet placement on the Carter WCFB and AFB (H.A.M.B. friendly carburetors):

Every WCFB and AFB I have ever seen or studied have the larger diameter jets in the primaries because of the metering rods or step up rods that protrude through the jets. Yes, many of these carburetors have secondaries larger than the primaries, but because of the rods, the larger jets are in the primaries.There is at least one AVS exception to this, but the AVS is not H.A.M.B. friendly, and (opinion) the only reason to ever use an AVS is a numbers-matching show car that is only driven off the trailer onto the show field. In 1968 when Chrysler started using these emission carburetors, wealthy MoPar buyers threw them away about 7 nanoseconds after they got the car home, and replaced them with either an AFB or a Holley. Once the vehicle went out of warranty, less wealthy MoPar buyers did the same thing! So we don't need to talk about their calibrations.

And if you guys print off this post, remember to print it on fiber (soft) paper so it may be repurposed!

Jon

 

We did it bois!!!

It was those damn metering rods this whole time!

Once I was convinced that the wrong ones were in there, I went over to my spare engine and pulled the metering rods out of it. Sure as shit, the factory (Standard) 75-824 rods were in there. I threw 'em in the convertible, took her for a drive, and she's a TOTALLY different vehicle. I couldn't believe how nice she drives now.

Funny enough, it's not at all surprising that the wrong rods were in there. When I initially rebuilt the carb, every single adjust was so out of wack it was insane. There were even small misc pieces that were missing. That spare engine donated those parts as well.

I've been trying to make sense of those rods though, just for the sake of trying to understand their thought process. The only thing I can think of, is maybe the floats were adjusted really high, causing her to run really rich. Instead of fixing that, they installed these super lean metering rods to try to fix the rich issue. Who knows though, it's fixed now and I suppose that's all that matters.

Anywho, I guess the morel of this story is, don't assume a stock type of vehicle is totally stock and un-messed with. Even totally stock looking Packard's can be screwed with by people that don't know what they're doing.

Thanks for all the help fellas, I SUPER appreciate it!

-Chris

 

I didn't know that at the time, but realized this rather quickly when trying to figure all of this out. It's pretty interesting how they did that.

Yeah, I did mention that the carb was from a 53 Packard, but I did not list the tag number because the carb didn't have one. I believe it should be a 985, but without the tag confirming it, I didn't feel comfortable stating that it was.

-Chris

 

I would have posted the tag initially, but it's been missing since I have owned the car.

Thank you for the kind words regarding the research I've done. It's been an interesting journey thus far.

As I'm sure you've read above, she's all good to go now. Once I get this whole garage project finished, I plan to do a proper adjustment of everything. All the tune-up related parts are brand new, but she's all tuned by ear because I don't have access to all of my tools and what not. With that being said, she runs great considering I haven't adjusted everything per factory specs.

I agree, we're still always learning, which is why communities like this are so important. Hopefully this thread will continue to help others way down the road.

Thank you,

-Chris

 

Whoa Jon! That's so much incredible info! I can't tell you how much I appreciate all that knowledge being passed into this thread. Between this thread and the big WCFB thread that you created awhile ago, there is a wealth of knowledge on this forum to keep these great carburetors on the road for many years to come.

Thank you again for all of your help. I SUPER appreciate it!

-Chris

 

Could be. I've seen this kind of thing quite a bit in different automotive discussion forums. And done it myself too.

Carburetors have to be setup carefully on the bench and after installation things checked adjusted in a certain specific order, because if a particular value or expected range isn't met or is out of allowable specs, then the tendency will be to try and compensate for that defect in one area somewhere else, downstream from it, or in a different circuit and the errors will stackup or likely compound from there.

Good work, and after all you're the one that did all of it. Very cool car! I bet it's fun to drive, and of course even more fun when it's running right.

 

You mentioned that you were missing some parts when the carb was first worked on.
It sound like the vacumeter piston or the metering rods are not in place or the piston is not working. The RPMs you are having the drive-ability problem is the transition between idle and WOT. The power valve parts you have should be checked for being in place and operating as designed. on the WCFB the PV linkage can be adjusted to elevate a stumble or hesitation. Check your vacuum and mechanical advance operations to verifiy they are working as designed.

 

GUESSING here that this was just a question of a previous "rebuilder" not understanding what they were doing.

The rods you have are from a 1954 Packard WCFB. Carter increased the primary jet size by a LOT for 1954, and then sized the rods accordingly.

Possibly, this individual had a couple of WCFB's and "made one from the best parts of both". When we were still restoring carbs, quite often we would get this request. No one every liked the answer!

Jon.

 

Yeah, maybe just one setting was out of spec and the dude just started adjusting everything else just trying to figure it out. Who knows.

Thanks dude! I really appreciate it! I'm glad I didn't let this thing beat me. I've heard such good things about these WCFB's so I really didn't want to ditch it, plus, I want to keep the car all stock, and an aftermarket carb would have looked terrible.

Dude! She's a blast to drive. She was fun even when running like crap, but now she's incredible. It's nuts how well some of these old cars drive. I really didn't expect it.

Thanks again Truck64! I really appreciate all the help and kind words.

-Chris

 

Thanks for the help Rick, I got it figured out before your post.

-Chris

 

I can't help but wonder if at one point after it was parked for awhile, someone got out there and tried to get her running. When I got her, the passenger side inner fender access panel was removed and some clear (very old & hard) pvc hose was hooked up to the mechanical fuel pump. Maybe the dude was dicking around with the carb and jacked it all up.

That's very interesting about the 1954 rods. I wonder why Packard decided to reconfigure the mains like that in 54. Wait a second! As I'm typing this, I just remembered that some models got the 359 (aluminum head) engine in 54. I believe those models got the WCFB 2112S. Are they from that engine by any chance?

Even then, I wonder why they would reconfigure the mains to that degree just for a slightly bigger engine?

Haha! I wouldn't do those rebuilds either. That may very well be what happened in this case. I suppose I'll never find out.

Thank you CarbKing! I super appreciate your help and insight.

-Chris