73 cj5 hot air choke - JeepForum.com
 
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post #1 of 6 Old 03-16-2009, 07:33 PM Thread Starter
dsfordguy
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73 cj5 hot air choke

Hello I have a 73 cj5 with a 258 1bbl engine and I am having a problem with a vacuum leak where the hot air choke tube connects to the exhaust manifold on my motor. Could someone post a pic of how the choke tube should be connected to the exhaust manifold on a 73? Thanks. I have no idea what it should look like because I bought the jeep like this.

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post #2 of 6 Old 03-16-2009, 09:33 PM Thread Starter
dsfordguy
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Is the choke supposed to suck air in? Also the po rigged the choke tube up to the outside of the exhaust manifold with a half metal cylinder hose clamped to one of the exhaust runners.
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post #3 of 6 Old 03-16-2009, 09:40 PM
computertech
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No, it does not suck air in, it pushes it out. The heat from the exhaust heats the spring in the choke mechanism, causing it to expand, therefore opening the choke. The copper tube plugs into a hole in the exhaust manifold just to the left of the base of the carb. It just sits in there. Mine has some kind of heat sleeve over the tubing. Oh, if you try to loosen the nut that holds the tubing to the carb, be sure and hit it with some PB Blaster or WD-40. (When the engine's cold of course) I broke mine, now it's held on with duct tape. As for your vacuum leak, it's probably just a rotted hose.
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post #4 of 6 Old 03-17-2009, 12:01 PM
John Strenk
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Quote:
Originally Posted by dsfordguy View Post
Is the choke supposed to suck air in? Also the po rigged the choke tube up to the outside of the exhaust manifold with a half metal cylinder hose clamped to one of the exhaust runners.
Quote:
Originally Posted by computertech View Post
No, it does not suck air in, it pushes it out. The heat from the exhaust heats the spring in the choke mechanism, causing it to expand, therefore opening the choke. The copper tube plugs into a hole in the exhaust manifold just to the left of the base of the carb. It just sits in there. Mine has some kind of heat sleeve over the tubing. Oh, if you try to loosen the nut that holds the tubing to the carb, be sure and hit it with some PB Blaster or WD-40. (When the engine's cold of course) I broke mine, now it's held on with duct tape. As for your vacuum leak, it's probably just a rotted hose.
Well actually it does suck.

It draws fresh clean air from the carb here:



Through this hose and tube which goes into the bottom of the exhaust manifold:


From the top of the manifold it goes through an insulated tube into the choke housing


There is a slot in the side of the piston bore that allows the hot air to be drawn into the housing as the piston is drawn down.



The exhaust heats up the air being drawn through this tube and warms up the spring inside the choke housing allowing it to open up the choke quickly.

So there could be a vacuum leak around here somepalce.

Sounds like the PO kinda knew what to do by running a pipe along one of the headers to warm up air being drawn into the housing. It should be filtered air though before it jams up the piston inside the choke housing.


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post #5 of 6 Old 03-17-2009, 03:32 PM
crusty75
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Here is a shot of how I "created" a hot air choke with the headers. Just like John posted above. I needed to experiment a little bit with the length and placement of the aluminum tube to get the thing to transfer the proper amount of heat. You can also "adjust" how it works by loosening the three screws that hold the plastic choke cover so you can rotate it a bit to get the drive-ability the way you want. I tried a piece of copper tubing, but settled on the aluminum tubing wire tied in only one spot. This allows me to adjust the plastic choke one notch rich in the winter and back it off to the middle of the range in the summer to get the drive-ability the way I like.

The "inlet air" attaches to the carb at the port shown in Johns illustration for filtered air. If you inspect John's diagram above, you will see that the warm air choke is really a very small controlled vacuum leak when operating properly. For this reason, if you have the little pipe to the choke capped now, and you hook up something like this, you will have to readjust your carb for optimum performance. The set up works quite well once you get it dialed in. Temps here run from 115 in the summer to the low teens in the winter.

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post #6 of 6 Old 03-17-2009, 03:39 PM
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Nice set up!!

What's on the other end of the pipe?


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