WCFB Carter Help Needed

[CA Victoria]

I have a rebuilt WCFB & the secondaries are not opening. It was recently rebuilt and was tested by the shop before I got it.
Recently noted the problem and I don't think they have worked up to now. As far as i can tell there aren't any physical restrictions, after engine warm up the counter weight air valve is free to move.
Trying to troubleshoot it before I call the shop after the Holliday.

[Charlie ny]

Tim,
There is default linkage do dad somewhere on the base of the carb that
prohibits the secondary throttle plates (not the vac controlled flapper ) from open-
ing if the choke is even partially engaged........providing in the interveneing 55 years
no one has messed around too much with it. The 2ndary throttle plates are usually
not tied with a hard piece of linkage to the primaries instead there is a wound spring
with an arm connecting the 2ndaries to the primaries.
Charlie ny

[Barn Junk]

On most WCFBs the secondaries will not open if the auto choke is closed, Assume you checked that. Also some WCFBs will not open the secondaries until activated by a vacuum diaphragm. Some others have flapper valves in the secondaries that stop the air flow until the manifold pressure is enough to handle the added flow. Need to know what WCFB you are working with.

[CA Victoria]

I did some more checking and testing. Watching this online video it shows the secondary butterfly damper butterflies opening well on a hard acceleration. My butterfly linkage connected to the choke is working well. The primary/secondary linkage is working on mine but on hard acceleration the butterfly's just barely move thus restricting the air flow. I understand this is controlled by airflow? and is not adjustable. The carb is from a 52 Buick and I have it on a 239 v8.

When I hand throttle the engine should I be able to see the butterfly open?

https://www.youtube.com/watch?v=ZSVCd3wryEQ

[Charlie ny]

Tim,
Is the flapper which is above the throttle plates the 'guilty' party here ? If so
remove it, The early Rochester I'm running on my '41 does not use the flapper, it
came into use in the 2nd generation Rochester 4 brls. You may end up removing some
counter balancing weight from the ends of the flapper to get it to 'tip' quicker.
Charlie ny

[Andy]

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If the choke is open, moving the throttle arm should open all butterflies. The flapper is independent and works on air flow. I have the exact carb on two engines and they work perfectly stock.
Is your throttle linkage opening the carb all the way?

[CA Victoria]

I found two different WCFB manuals and it does not address the flapper or secondary operation enough to troubleshoot.
I may be expecting to see more movement than what the airflow will allow by hand throttle.
I have some flapper movement but less than what is shown in the attached video ( post #4)

[Charlie ny]

Tim,
Ahh yes, I see the flapper counter weight in your photo, the ancient
Rochester I'm running is a first generation '52 and does not have a flapper at all.
I'd try removing the flapper and see what happens. These early 4 brls had pretty
small venturiis I think it's worth a shot or try lightening up the counter
weight. This may or may not be significant but on the Fenton intake I'm using I
milled out the area between the front and rear bores, I did however leave the
divider between the RH and LH bores.
Charlie ny

[Kahuna]

CA Victoria
I don't think the secondaries will open unless there is a load on the engine. Merely opening the throttle by hand will not open the secondaries

[CA Victoria]

I was reading some last night and came to that same conclusion Kahuna.
JWLs book has some great insight into the 4bbl intake which relates to NY's post. As long as the linkage is set up correctly and the flapper weight and butterflies are not altered they won't open until the load is sufficient.

Thanks y'all'

[tubman]

Originally Posted by Charlie ny

Tim,
Ahh yes, I see the flapper counter weight in your photo, the ancient
Rochester I'm running is a first generation '52 and does not have a flapper at all.
I'd try removing the flapper and see what happens. These early 4 brls had pretty
small venturiis I think it's worth a shot or try lightening up the counter
weight. This may or may not be significant but on the Fenton intake I'm using I
milled out the area between the front and rear bores, I did however leave the
divider between the RH and LH bores.
Charlie ny

Charlie,

Can you explain why you did this? I know enough about you to know you're not one of those guys who do things like this "just for the hell of it". I have both Edmunds and Fenton 4BBL manifolds (8BA), and I have rebuilt a Rochester from a '53 Olds and a WCFB from a '54 Chrysler I plan on using. Any insight you can supply would be appreciated.

[Charlie ny]

Tubman,
I was searching for a smoother transition from primaries to 2ndaries. This
change took out the harsh gear snap transition. Keep in mind my ancient Roch 4 brl
does not have a flapper, this change help significantly.
Charlie ny

[tubman]

Charlie,

Thanks, that makes sense. My Rochester is only one year less ancient that yours, so I'll keep this trick in mind.

Tubman

[40 Deluxe]

Not impressed with that carb in the video in post #4! It has a bad bog when the throttle is snapped open, around the 40 second mark. If it bogs like that without a load on it, think how bad it will be in the car when you floor the throttle at low RPM's! Especially on a 239 engine!. That carb was designed for a 331 or so engine. Removing the flapper or even just lightening the counterweight will only make it worse. Opening the secondaries before the engine needs that much air will only kill airflow, cause an extremely lean condition and you will hear POP, POP, POP back thru the carb.
Reminds me of the guys who cut coils off the secondary spring in their Holley 4 barrel until they can "feel the secondaries open up"! Hah! Only thing they did was cause a bog!

[tubman]

I am also not impressed that he says it is from a "324 slash 250 Horsepower with manual transmisssion" from a '63-'64 Corvette. Later on he says "that is a beautiful runnin' carburetor". Either they have an Olds engine swapped into the Corvette or the guy doesn't know what he's talking about. I'll take the latter, because of the "beautiful runnin'" part.

[Charlie ny]

Just to keep things on track, in Tim's initial post regarding the flapper not opening all
the way on his WCFB, there was NO mention of a bog at all. The answer to his situation became clear once it was realized the carb was being operated under no load conditions. This small WCFB
is a great carb for Flathead applications and you must look the test being performed in post #4. Beneath the carb is a riser which may or may not be causing things to act up. I'll will wait to get Tim's report on the carbs performance under real world driving
conditions with engine at operating temps. This carb is a good one, it may require
a bit of tune is all.
Charlie ny

[CA Victoria]

I tied the flapper up today and went for a test drive. Since the linkage is opening properly I will conclude the WCFB is working as it should acknowledging that the secondaries will open when the load is sufficient. Since I cannot see the carb while driving I'm going by seat of the pants response and air flow sound.

[Charlie ny]

Tim,
How'd it go with the flapper tied open ? The unvarnished facts .
Thanks,
Charlie ny

[CA Victoria]

Well......I believe the carb is working as it should. But I dont have a base for comparison. I'm still not satisfied that It is @ full potential. While this is not a high performance engine, with the little cam and 7.75cr. I'm wondering if I could be a little under carburetated? It definitely has better acceleration than a stock engine. Info states this WCFB was used on a Buick v8 (est. 375 cfm). I have an AFB from a Buick 340 which has a little larger bore (+1/8) that may help it to breathe better. The charts show CFM compared to CuIn and a 350 is recomended for a 250 CuIn engine. The next step up is a 500 cfm which seems like to much....Your thoughts?

BTW, The ignition system is working well.

[CA Victoria]

I found a carburetor size calculator on line. A 250 CuIn engine at 5000rpm only requires 365 cfm flow. Where at about half throttle it only needs about 180 cfm flow.