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WCFB carb questions

9K views 45 replies 7 participants last post by  f.i.57chevynut 
#1 ·
My carb is correct for a 57, but may have be restored (before I bought it) to suit a larger motor. And on first run it was chugging a gallon for every six miles. It's had a bit of work done since and is running MUCH better.

But I probably want to check on what sized jets should be in the thing and what strength/colour metering rod springs should go with it. (The engineer who built the motor had said I should have the softest springs available to keep it super lean when driving at speed.)

Anybody got any figures (or spring colour reference) for me? (Currently has the green springs.)
 
#2 · (Edited)
Oh, come on, John - can't you think up any DIFFICULT questions? :)

Your Carter 2505S (for automatic transmissions) should be equipped as follows:
1. primary metering rod jets 120-165,
2. primary metering rods 75-1349,
3. secondary metering jets 120-177, and
4. low speed jets 11-302S

There is no identifying marking on the power valve vacuum piston spring (which operates the metering rods). But, the 2555S (manual transmission) and 2505S (automatic) do use different springs.

Additionally, just to make sure you've got the right carburetor - the air horn should be 6-1289S, primary throttle plate 2-92, and secondary throttle plate 2-166 or 2-171.

(yes - I have an original Carter parts catalog and an NOS WCFB rebuild kit)
 
#28 ·
Oh, come on, John - can't you think up any DIFFICULT questions? :)
Ok, Stovee!

The carb guy took a look at it last week and started murmuring. I figured that was a good sign. First thing he said was the throttle shaft was loose and that needed re-seating. He mentioned drilling, a teflon bush and filing by hand. Another good sign. Then he got a (or table) machine to stand took readings from primaries and secondaries. CO2 readings were 8 for both. More murmuring. What would you think the readings for both SHOULD be once remedied?
 
#4 ·
I believe the top number is 1271. 6-1289 may be a part number but the cober itself has the 1271 on the right rear. You could get the spring out of a 58-61 dual quad. It's the lightest spring I've ever seen in a WCFB, but you may see a flat spot when you jab the throttle. It's hard to believe that anyone would have installed a heavier spring under the power piston. To tell is it's way too heavy take the metering rod cover off and start the engine. The metering rods should stay down all the time while idling. If not, they may "dance " up and down a little if the camshaft is larger than the original or a close replacement. If the metering rods don't stay down you can cut a coil off the spring and try it again. Good luck. Tom
 
#5 · (Edited)
Tom, now that you mention it, I do recall that to be correct.

6-1271 appears on the air horns used in production, but the catalogs (Chevrolet and Carter) list 6-1289 as the service replacement air horn.

I agree on the vacuum piston spring - it has to be matched correctly to the application, or you may introduce a flat spot (either too rich or too lean). A really weak spring would be good for big cams, but may cause a lean stumble on heavy acceleration with a standard cam.
 
#6 ·
Thanks, gents. Sounds like great advice. Hope my mechanic does not get grumpy when I start shooting my mouth off with my new-found knowledge!
 
#8 ·
I still haven't had a chance to look at the numbers yet, but I can tell the carb is still running too rich, even thought it's been adjusted to lean as much as possible. (10 degrees timing, btw.)

So we are thinking it needs new (correct) jets, metering rods any anything else associated directly with those parts, as far as sizings go.

Where do I go for these parts? I don't need a general re-build kit, that's already been done. It's just these parts I need? (Danchuk have sets listed, but only for 2x4.)
 
#16 · (Edited)
... and .076 for the secondaries.

Like I said, I have a message sent to Chuck Smith, but it's still the weekend where you are so will wait another day.

Have also done a look on various carb parts suppliers in the US – none of them seem to stock (or are out of stock of) metering rods – Chuck Smith included. Does that sound strange? One crowd said they would make them to order.

Also, when ordering the jets, should I order additional one size down for each, just in case I need to go even leaner?
 
#10 ·
Thanks, Tom.

I have sent a message off to GS. And also have read some of your other postings on the subject.

Before I go and order anything, though, should I be double checking what I have? How hard is it to identify a WCFB while on the car? How may of the parts can I sight casting numbers for by just taking the air cleaner off and taking close-up photos? (I can't really get to it now as it is on display in a show.)

And even if it is off by a year or so, would that change the specification of the jets and metering rods that I would want?

Cheers
 
#11 · (Edited)
Every one of the part numbers I mentioned is stamped on the part. You may need a magnifying glass to see the numbers clearly, but they are there.

The 283 was available with a 4 bbl up until about 1961. So, any of those years would be properly sized for this car.

Note that you might have a WCFB that was designed for the '58-61 348. I have a '58 348 WCFB on the shelf at home (that's a first-rate mess). To the casual observer, it looks just like the '57 283 WCFB.

Best thing to do is take it off the car, disassemble it, and inspect it piece by piece. But, before you do that, make sure the power piston "T" rod operates smoothly when you press on it, and retracts fully when idling.

My bet is the float level is off, or you have a defective needle and seat (which also would cause a too-high fuel level).

The main things you can check on it while on the car are the part numbers on the air horn and the main body. That will at least tell you whether it's a '57 or not. Checking the power piston requires removal of 2 screws. You can also reach the metering rods while that cover is removed. Everything else requires taking the air horn off. You can do that on the car, but reading the numbers will be harder.
 
#12 ·
The reason I mentioned the actual size of the jet is because some people think that the more gas you put into the engine the more power you get, not realizing that you need the appropriate amount of air to burn the gas properly. I have numbered jets that other people have hogged out, so the numbers don't correspond to the actual hole size as prescribed. Metering rods not much modifying, except by me for some custom tuning on a hodge podge Olds carb for my dad's 265.
 
#13 ·
This is going to sound weird and counter to what logic would indicate but starting with a stock 283 Power Pack engine with 2555SA carb, Duntov cam and solid lifters, I took the metering rods and filed/sanded them down to a uniform diameter (the size of the bottom of the rod), then switched the position of the (stock) jets, primaries into the secondary holes and vice-versa. This had the effect of running slightly lean on the primaries and rich when the secondaries opened. I was still able to get a max of 25 MPG on the highway. My overall mileage was down around 12-13 MPG.
 
#17 ·
And what do y'all make of the 10 degrees timing currently set? What is that saying about the rest of the set-up?
 
#19 ·
Can anyone confirm the size of the secondary jets? Chuck Smith (who I just spoke to) thought that .076 sounded too small.

Also, if I can get local parts otherwise intended for Edelbrock but are the correct thread and opening, can I use those? (Just way quicker and less PITA with postage than buying from the States.)
 
#20 · (Edited)
.076 is correct. See page 6m-57 in th e '57 shop manual.

Note that the .086 "primary jets" are bigger than the secondary jets. That's because a) there's a metering rod sticking through the .086 primaries, which reduce the effective diameter, and b) there are .031 low speed jets feeding the primary as well.

Yes, that's right - there are 4 jets (not including the idle circuit) on the primary side of the WCFB.

As far as using Edebrock jets - I'm about as confident telling you that will work as telling you to use the jets out of a Zenith carburetor on a Ford 9N tractor rusting away in some farmer's equipment shed. Check what you've got, prove it to be correct, incorrect, or damaged, and order parts appropriately.

The thing is - when these carburetors meet all factory specifications, they will work well. So, first thing is to get them to that point, rather than playing a guessing game.
 
#21 ·
One thing to consider here is how far off a 283 carburetor can be, and still work. The 283 is a very "forgiving" engine.

One rather "interesting" friend of mine is fond of saying that a 283 would run if you pulled the carburetor off and just stuck the fuel line straight down the intake manifold. That's an exaggeration, of course, but his point is well taken.

The only way to start with this problem, IMO, is to step through every piece of the carburetor, ensuring you have a stock part that meets stock specifications. Somewhere in there, there's one or more parts that aren't - and that's why your gas mileage is so poor.
 
#22 · (Edited)
But - before you pull off the carburetor, check that your fuel pump pressure is between 4 and 5.25 PSI. Yes, you read that correctly. (page 6m-68 in the '57 shop manual) Later small block pumps have higher pressures.

Even a perfectly rebuilt carburetor will run rich if the fuel pump pressure is too high. The pump will overpower the needle and seat and cause the fuel level in the bowl to run too high.
 
#23 ·
Just checked some numbers:

Top – 6-1271
Bowl – 1088
Base – can't see that with the carb still on the manifold, or is it hiding somewhere? (Or does it not matter, given the other numbers?)

And asked the mechanic about the fuel pressure – he's sure it would be no more than 5 pounds, seeing as it is mechanical. Do they ever play up and provide more?

Mechanic also said he checked the floats – all ok, and checked the needle and seat – all ok.

Have found a local guy whose family have run a carb shop since 1953 and they have all the jets and metering rods required, so will take it all up to them to check parts and numbers on Saturday or Monday.

Still not running great. Was fine when last tuned, but another 50 miles on it and the thing is getting rougher. My guess is the plugs are getting blacker and wetter by the mile.

Will report back. Thanks for all the advice, gentlemen.
 
#30 ·
That'd be C0 (mono), I guess.

Re brass, the carb guy reckons that teflon is better, since it is self lubricating. And easier to fine tune for fit.

And yes, the throttle shaft issue would not be the whole cause, if any, of the economy issue. But he wanted to get that right before doing anything about the jets etc.

It won't be in his shop until Monday week – he's pretty busy and we've had public holidays making our working weeks shorter lately. I'll report back after then.

Cheers
 
#31 ·
I can see his point about teflon bushings. I've seen graphite impregnated brass ones as well for sale. But, I don't repair carburetors for a living, so I'm not going to argue with him.

I'm still trying to figure out what you mean by "CO2 readings were 8 for both". If you mean he connected your carburetor to a carburetor airflow testing machine, and measured the air/fuel ratio on primary and secondary is 8 to 1, then yes - you have a huge problem.

Since the "ideal" air/fuel ratio is 14.7 to 1, an 8 to 1 ratio would explain your horrible fuel mileage. 8 to 1 is more like what you'd use with the choke full on to start the engine. Incorrect or drilled-out jets are likely culprits, as are incorrect metering rods or metering rod springs.

At this point, I'm going to step back. PM me if you need additional specs on the original components.
 
#32 · (Edited)
The carb guy hooked up some sort of portable tester – a hose to one of the exhaust pipes and then the box gave readings. It read what I understood to be CO (carbon monoxide) as an indication of richness. It was reading 8% off both primary and secondaries, where it should have been 1.5% off the secondaries and something closer to 3% off the idle. So that is where the scope to improve on the economy lies.

Like I said, he's going to fix the throttle shaft first and then work on the jetting. He said he would start with the standard sizes first and then tweak (not twerk) from there.

Btw, had been invited to display my car at one of the annual vintage and historic track race meets today. Was heaps of fun and was in a great vantage point for the races.
 
#33 · (Edited)
Okay - that is correct.

The tester used probably tests for CO and HC. CO is carbon monoxide - fuel that couldn't burn completely because there wasn't enough air. HC is hydrocarbons - fuel that didn't even attempt to burn, usually because of faulty ignition or burned exhaust valve.

No question it's running very rich.
 
#37 ·
I would inspect the shaft for wear. It seems to be the real wear part of the carb, not the base casting. Most of the WCFBs i've taken apart have worn through the chrome plating on the shaft. I know Chuck Smith has shafts for the 2x4 carbs but I don't know if he has them for the single quad. The angle of the secondary butterflies may be different since the single uses a 166 and the 2x4 uses a 193.
 
#38 ·
Ok, the car (and carb) spent a few hours with the man in Thornbury today. Here's what he found:

The throttle shaft, previously thought to be loose, was ok. It was the linkage from it that was loose, so that was re-peened.

The main problem was coming from one of the metering rids, which had become dislodged.

Jets were fine, as it turned out.

Fuel pressure was good at 5.2 psi.

Idles were re-set and CO read at 1.6%. Better than the 8% previously.

But he did find that the engine was running 1.7% richer with the air filter fitted. So it looks like my configuration of a 3" paper filter within the original 4-barrel cleaner is actually restricting air flow. Maybe a 2" filter is ok, and the additional flow over the top of the thing (unfiltered) will be ok?

Anyway, I'll fill the tank in the morning and take another reading of fuel (un)economy in a week's time and see if it improves from 8.9 miles/gallon.

Thanks everyone for the comments and assistance.
 
#39 ·
John, that is good to hear that you found the reason for your carb problems. What is interesting is the 3 inch filter causing air flow issues. Could you post some pictures of your modified air filter? I would think that the shorter filter would cause more restriction. Let us know what you find when changing to the shorter filter.
Tom
 
#41 · (Edited)
Could you post some pictures of your modified air filter?
Here you go, Tom.

I cut the top off the old oil bath filter to serve as the clamp, otherwise the new filter would have just rattled around. It turns out that the new assembly, with the 3" paper filter, is about as high as the old, so the standard threaded post and the two wing nuts work as per usual.

It might be that the paper filter restricts the air flow as much as an original one did. I mean, there has to be some resistance there, otherwise it would not be a filter! It's less than 2% difference with or without. I'll run it for a while and see what the mileage is.



Put new plugs in it this morning, and it sure runs much better!
 
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