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krinkov58

1952 Carter WCFB...setting idle...

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I have a 1952 Buick Roadmaster and just rebuilt the Carter WCFB carb, and I'm setting the idle according to the factory manual.  The manual says to back out the throttle stop screw and hold the fast idle cam in the "choke open" position, then screw in the throttle stop screw until it just contacts the throttle lever arm, then give it another full turn.  This should give it an idle speed of 450rpm.  I'm getting more like 700-750rpm at the least.  Any thoughts?  Both idle needle valve are backed out one full turn off seating.

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These sound like initial settings when assembling a carb. The final settings will be different. The caveat is the throttle should never be quite all the way closed.

 

Look for vacuum leaks and verify your ignition timing.

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Right, the needle valves being backed out one turn from seating is the ballpark you start off with, then in and out until you get the mixture correct.  The manual says do this at a 450rpm idle but no matter what I do, I cannot get that low.  Even with the throttle stop backed out all the way.

Here is something I forgot to mention though...I have a 1/4" phenolic riser (plus the width of 2 gaskets, one under the carb and one under the riser) underneath the carb to stop heat soak...so the carb is sitting slightly higher than it's stock position.  I had to make a lengthened choke stovepipe to compensate.  Would this affect idle speed?  I would think it would affect the top end rpm instead.

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1/4 wont make any difference you can notice. If the gasket and the manifold have 4 holes, and your spacer is open, that could have some effect. I don't have a manual for that car handy, but low settings like that are almost always in gear if the car is an automatic. I'm guessing this has Dynaflow.

 

Length of choke stove pipe wont make any difference.

 

Leakage through slightly worn throttle shafts can make some cars run a bit high, but probably you can still come close.

 

Badly worn throttle shafts will cause the butterflies to catch under return spring pressure, and not be closed all the way even though the throttle stop is all the way out. Try backing the stop screw all the way out, plus a little, then jiggle the lever on the throttle shaft. Jiggle it front to back with regards to the car.

 

Check to be sure your secondary throttle plates are closing all the way. They should be. All idle air should be coming past the primary plates (or through the idle jets along with the fuel).

 

Is the vacuum advance on the distributor connected to the correct port?

 

Let us know how it goes.

Edited by Bloo
.. (see edit history)

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 did you remove the butterflies from the shaft when you disassembled? The butterflies can go on four ways but only one way is correct. 

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Thank you gentlemen for your replies

Bloo, nah it's not an open riser.  Just one of those 4-hole phenolic jobs to try and keep the gas from boiling when the car is shut off after a long drive.  Yup a Dynaflow...it's been flowing onto my garage floor for years.

I mentioned the stove pipe length just to show that it was a little bit of a height raise with the riser+gaskets, couldn't get away with just bending the stock stovepipe length.

I'm going to check that throttle shaft tomorrow though, I hadn't thought of that!  Secondary throttle plates do close all the way though, and the vacuum advance can is hooked up right...everything is peachy otherwise but it just is really idling high.  No vacuum leaks either.  

Beemon, no I did not disassemble that far.  

Old-tank, I did and no drop in rpm

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If you can, disconnect the heat stove and put a vacuum cap over it for testing. If the pipe doesn't seal in the manifold, it can cause a vacuum leak. I would also check the base of the carb for vacuum leaks, though it sounds like there isn't much issue there. If the issue goes away after plugging the heat stove, then pull it back out and slather some RTV on the end that goes into the exhaust manifold. This area shouldn't cause any issue due to the choke valve piston, but I had this issue with my WCFB. I also installed the butterflies backwards and it wasn't making a positive seal in the bore :ph34r:. Only other thing I can think of is idle screws may be out too far. If it still idles with the throttle screw backed all the way out and the throttle lever off the carb, pulled fully shut, then you have a leak below the throttle plates.

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Beemon, I did test the throttle shaft for play and there is some, barely perceptible but there is a tiny bit wiggling from front to back.  Not 100% sure it's the shaft or what is attached to it.  I set the fast idle cam as per the manual, it was slightly off but not by much...

Disconnected the choke heat pipe and blocked off the orifice with some rubber...no change

Disconnected the linkage and tried to get it to stall by closing the throttle all the way by hand...got it to almost stall but could not get it to get below about 300rpm.  So it looks as if it could be a intake manifold leak.

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1 hour ago, krinkov58 said:

Disconnected the linkage and tried to get it to stall by closing the throttle all the way by hand...got it to almost stall but could not get it to get below about 300rpm.  So it looks as if it could be a intake manifold leak.

 

If it goes down to 300 shut, thats good enough isnt it? You were trying to get to 450, right? It only has to be open a little.

 

It is not commonly talked about, but the fuel that comes out of the idle jets is already mixed with air. Some cars will idle slowly with the throttle shut. 300 rpm is close to stalled,  and the idle jets would bring it a tiny bit slower if they were properly set.

 

I suggest you have a closer look at the bushings. If you can wiggle, and get the throttle further shut, this could be the issue. The throttle plate catches on the bore, and doesn't let it shut the rest of the way. You wouldn't notice this on the bench because there is no return spring attached.

Edited by Bloo (see edit history)
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A Holley engineer once said (at a seminar I attended) that the air bleed via the throttle shaft was calibrated for, but if it gets lose enough to let the base idle "seating" not happen reliably each time, then re-bushing or a new throttle body was needed.  I believe it's the "main tube" fuel that is emulsified with air before it gets to the venturi?  The idle fuel tubes are solid brass, drilled and such.  The main tubes have air hole in them.  On each respective venturi cluster, at the top, before the two fuel tubes go to where they end up, each has an "air bleed", which is a mixture calibration point (also).  When they clog or decrease in size, that one circuit will become richer in nature and "full rich" when it's fully closed.

 

NTX5467

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20 hours ago, Bloo said:
21 hours ago, krinkov58 said:

Disconnected the linkage and tried to get it to stall by closing the throttle all the way by hand...got it to almost stall but could not get it to get below about 300rpm.  So it looks as if it could be a intake manifold leak.

 

If it goes down to 300 shut, thats good enough isnt it? You were trying to get to 450, right? It only has to be open a little.

 

It is not commonly talked about, but the fuel that comes out of the idle jets is already mixed with air. Some cars will idle slowly with the throttle shut. 300 rpm is close to stalled,  and the idle jets would bring it a tiny bit slower if they were properly set.

 

I suggest you have a closer look at the bushings. If you can wiggle, and get the throttle further shut, this could be the issue. The throttle plate catches on the bore, and doesn't let it shut the rest of the way. You wouldn't notice this on the bench because there is no return spring attached.

Edited 19 hours ago by Bloo (see edit history)

Check the external linkage for adjustment or binding; also the spring(s).

Maybe even check the engine/tranny mounts and thrust pad if the external linkage seems out of adjustment.

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Took a couple of days off just to come back and look at things fresh...tinkered around a bit with the linkage etc. and got it to idle a little better but still not great.  Now it has a bog coming off idle that wasn't there before...

So I'm going to borrow or buy a different tach and vacuum gauge and see what numbers I can get.  I've been using a 1970's Sun setup and I just want to make sure it's not the 40+ year old equipment contributing here.  If I'm getting the same results, then it's back to work

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If it's got a bog off-idle, it can be because the throttle blades are too far open, physically, at your lowest obtainable idle speed.  As things are now.  Or it could be  the accelerator pump not working.

 

You might need to remove the carb from the engine, empty the gas out into a drain pan, then invert the carb and see just how tight the throttle plates "seal" the throttle bore with the idle speed screw backed all the way out.  The vertical slot near the idle screw "hole" in the throttle body, the transition port, should have about .040" of it below the throttle plates at base idle.  If more, it can cause a bog coming off-idle.

 

Please let us know what you find.

 

NTX5467

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