Question regarding 3X2 manifold: HELP

[RBurgeno#22418]

This tube that runs down the center runner of the manifold, what is this tube for ? Is it for heating or some kind of sensor ? I HAVE NO IDEA !
Thanks for your help,
#22418

[David King (kz78hy)]

My 58 does not have this tube in the manifold.  Does your heat riser tube from the RH side exhaust manifold connect to the center carb?  Maybe it connects to that.   I'm guessing this manifold is off of a 59 or 60.

Good luck
David

[Bob Schuman]

The tube in your manifold connects to the external tube that goes to the automatic choke. Exhaust gases heat the tube inside the manifold, and that hot air goes to the choke thermostatic spring inside the black round housing, to gradually open the choke on cold starts.
The tube inside the manifold must not leak. If it has any holes burned in it, which is common, exhaust gases will be drawn into the choke, very quickly fouling it and causing the choke to stick in an improper position.
Bob Schuman, CLC#254

[35-709]

Take Bob Schuman's advice about having no cracks in that tube to heart!  It looks like in the first picture that you do indeed have a hole in that tube! 

[quadfins]

Yes, this is the infamous "choke heat tube crack", endemic to these manifolds.

There are a couple of ways you can deal with it, depending on where you are located, and how absolutely authentic you want to be.

Where are you, and what are your plans for the car?

Jim Eccleston
1961 Coupe de Ville
BATILAC - a fellow sufferer of choke heat tube crack.

[RBurgeno#22418]

Take Bob Schuman's advice about having no cracks in that tube to heart!  It looks like in the first picture that you do indeed have a hole in that tube! 

Good eye Geoff, it's more like rotted away than cracked. Not a great place for rot or cracks !
And to Jim I'm located in Long Beach California and I'm not building a totally authentic 390 I want what's best for the motor. What are you ideas ?
Thank you all for you help it's exactly what I was looking for, great answers !
#22418

[quadfins]

OK, here we go.

I am in eastern Virginia, so your climate is even milder than here.

My choke tube is also rotted out. One option is to remove the old one, and have a machine shop press in a new one. This is the best option in cold climates, where the choke and idle speedup are more important. Also for those who desire absolute factory authenticity and operation.

I would recommend for you, what I did for my '61. Simple and inexpensive:

Get two self-tapping screws. Install one at the inlet hole in the bottom of the manifold, and seal it up airtight. Do the same at the outlet side (that is, the one at the top side of the intake manifold.) Position the metal tube that feeds from the choke housing to what would have been the hole right over the screw. It will appear to attach right into the manifold, but in reality, the air drawn in will be sucked past the screw. Eventually, the air will heat up, and adjust the choke as designed - just not as quickly, since the air is no longer going through the bypass passage in the manifold. You can adjust your choke accordingly, to make it as sensitve as you like. The main thing here is that the rotted choke tube is sealed off, and will not cause either an exhasut leak into the engine compartment, nor will exhaust gasses get into the carb.

This is one of the first projects I undertook on my '61, and I have never had any trouble with engine operation or carburetion. If you emsail me directly, so as to establich a direct connection, I can send you some pics of how my system looks. It is imperceptible except to the aboslute expert/purist. My home email is in the "Technicians" section on the CLC website.

The entire operation can be easily done in a Saturday morning. The intake manifold will have to be removed, to access the bottom hole, but it looks like yours is already out. Take it to a hardware store and get two self-tapping screws, paint the upper one mainfold blue, and you are done.

Feel free to PM or ask Q's here - I am always eager to help.

Jim

[Jeff Maltby 4194]

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=320350926954

[Bill Lucarelli #22702]

It's a pretty easy fix for a good machine shop.  I just had the tube replaced on my 59 Eldorado.  The tube is a smaller diameter than what is available today so my shop installed a slightly larger tube and it works fine.  My recommendation is not to block it off with screws, as my car, because of cracks in the tube, ran poorly in warm weather, caused the choke to stick on.  Good luck

[quadfins]

Hi Rob,
   I received your email, and I sent you 3 pics. Let me know if they don't get through to you.

Jim