Choke tube

[Summershandy]

I was crawling around the engine tightening and checking things and it occurred to me, when I was having the exhaust manifold machined the shop broke off this tube. I drilled out the old piece and used a high heat silicone to seal it back in. It's loose and my question is, will this have any affect on the carb's fuel/air mixture? The choke works fine BTW. 

Edited August 31, 2022 by Summershandy
add on (see edit history)

[Andy J]

I did the exact same thing! I made another line and just stuck it back in the hole. I don't think it will matter because the clearance isn't enough to let much exhaust escape. If it seems to be a problem,I'm going to braze the tubing in the manifold. I was so careful with that manifold,but when I took it to get it planed,I set it on the shop table and broke the thing off!

[Bloo]

No, no difference to the mixture, and if you sealed it where you stuck it in, no difference in anything. You probably didn't even need to seal it.

 

That isn't what it looks like. There is no exhaust in there. There is an open cavity in there covered up by a sheet metal plate with 2 holes in it. All it does is make hot air, which is necessary for the choke to work. The choke has a tiny vacuum bleed inside that causes hot air to flow up through the tube and make the choke work.

[john hess]

also, if you make a new tube, it should not bottom out in the hole. As bloo states, it needs to draw hot air for the choke bi-metal spring to open the choke...

[Summershandy]

Thanks for the reminder! I knew that but totally forgot again. How the memory fails when you've been away from the workings mind you, having to run a business and survive during a 2 year pandemic can really take a toll on the ol' brain!

 

[PONTIAC1953]

I stand corrected.

Edited September 3, 2022 by pontiac1953
correction (see edit history)

[carbking]

There should be a small amount of negative pressure (vacuum) in the tube.

 

There is a source hole in the carburetor throttle body for vacuum. This source travels through a passage to the back side of the internal choke pull-off in the choke housing, then bleeds past the internal choke pull-off to create a slight negative pressure in the choke housing. The choke tube is connected to the choke housing, thus acquiring this slight vacuum signal. This vacuum pulls the hot air from the manifold into the choke housing, warming the bi-metallic spring, allowing the spring to relax. The internal choke pull-off (which works against the spring tension) can then open the choke, as the spring relaxes.

 

Since the internal carburetor passage is small, a backfire can cause it to clog, thereby making the choke work extremely slowly, as the heat will come to the choke housing much slower.

 

One can externally test to see if the carburetor internal vacuum source passage is clogged easily:

 

(1) Acquire a Klee-nix tissue

(2) Disconnect the choke tube from the choke housing

(3) Start the engine

(4) Hold the Klee-nix to the vacuum port on the choke housing; if the choke housing has vacuum, the Klee-nix will remain in place after you release it.

 

A warped choke housing, or defective choke housing gasket can also be an issue for pulling the heat from the manifold.

 

Jon