59 CDV manifold

[Paul]

Hello - talking to another caddy owner he told me his engine always ran a little shaky. He said the problem was the manifold needed to be replaced. He said the choke tube rusted in the manifold and somehow affected the engine performance. After replacing the manifold it runs fine. Does this make sense? Can a corroded choke tube change how the engine idles and runs? Any clarification would be great. Thanks.

[Roger Zimmermann]

The rotted tube can affect the cold start behavior, plus it takes much longer to have the choke open. The tube can be replaced, but to do that, the old one must be extracted. It's easier to perform the job when the intake manifold is removed from the engine.

[Big Fins]

The rotted tube also creates an excessive vacuum leak.

[papas52cad]

Regarding the last comment about a vacuum leak...I had my carter AfB rebuilt last spring and added an electric choke ( this is for my 1969 390 motor)...therefore the carb/manifold heat tube vent hole in the intake manifold is now open with the tube left off since it is no longer used for choke..should this hole now be closed off...so there is no loss of vacuum?
A suggestion on how to close off hole effectively will be appreciated
Thank you
Peter

[The Tassie Devil(le)]

G'day Peter,

I would suggest installing a small threaded pipe plug using a sealant to stop the leak.

There should be no Vacuum leaking into that hole, as it only goes into the Exhaust crossover passage.   IF there is a vacuum leak, then the manifold would be internally cracked.

Bruce.

[35-709]

Yes, the vacuum comes from the choke housing to pull the heated air into the automatic choke assembly, which you don't have on your electric choke carb.  If your old heat riser tube is still in the manifold it may be rusted shut already but plugging it as Bruce said does the job.  Put your finger over it and see if there is anything coming out --- do it right away while the engine is still cold, don't want to burn your finger!   

[gkhashem]

We have discussed this before

http://forums.cadillaclasalleclub.org/index.php?topic=157025.0

[Lexi]

Should your manifold prove to be cracked, I think I got an extra intake manifold for a '59 Caddy that I would part with. Clay/Lexi

[INTMD8]

Regarding the last comment about a vacuum leak...I had my carter AfB rebuilt last spring and added an electric choke ( this is for my 1969 390 motor)...therefore the carb/manifold heat tube vent hole in the intake manifold is now open with the tube left off since it is no longer used for choke..should this hole now be closed off...so there is no loss of vacuum?
A suggestion on how to close off hole effectively will be appreciated
Thank you
Peter

The choke tube wouldn't cause a vacuum leak, just an exhaust leak.  It goes through the center port of the intake manifold, which is an exhaust crossover port.

One end to atomostphere, one end to the choke.

There is no vacuum at carb where this connects to the choke assembly.

(It would always then be a vacuum leak since the car was new as the other end of the tube is open).

If it is cracked and leaking, having switched to an electric choke you could plug the end but you would also need to plug the other end, underneath the intake facing the drivers side of the car to seal the exhaust leak.