'74 F100 2WD 302

Where exactly should the choke fresh air tube go to? I've reconnected the choke stove to manifold tube... but this other tube? Does it also go to the manifold? I've asked countless other folks who "should" know but nobody can tell me exactly where it might go.

BTW, I just replaced the rocker arms, most of which were showing serious wear, boy does she run a LOT more quiet.
Still, this fresh air tube is kind of bothering me.

Hey KingFisher, you were right, the carb rebuild kit is REALLY inexpensive and doesn't seem too difficult. I'll make sure I get help on the floats. Thanks for the kick in the butt to do it myself.

Jim, NC

 

One line from the choke stove goes to the choke housing. The other line goes to a port under the air filter mounting surface that leads to fresh air inside the carb. The system draws filtered air from inside the air filter thru the choke stove, past the bimetal coil choke spring and into the intake manifold.

 

You mention that there is a line TO the port under the air filter mounting surface, where does it come FROM to get this "fresh air". I can only find one opening in the manifold, and that's already taken by that other line that goes to the choke housing.
Thanks

 

There should be two holes in the top of the choke heat exchanger (the piece bolted to the intake manifold). The hole toward the rear has a tube connecting it to the choke housing. The hole toward the front should have a tube and short hose connecting it to the fitting under the back of the air horn.

The following pic shows the choke housing tube mounted in the rear hole and the front hole empty:



The fresh air source is the fitting on the back of the air horn. That allows filtered air to be pulled from the top of the air horn (behind the choke tower) down to the heat exchanger, through the exchanger tube coils, and then up into the choke housing.

The vacuum source that pulls the air through this system is a small port inside the right main venturi that exits the right side of the carburetor main body, next to one of the choke housing mounting screws. That hole (arrow in the next pic) connects to a drilled passage in the choke housing.

 

Bubba, You are THE man. But there is only one hole that i can find on the manifold.

 

Whoa. I wasn't paying close enough attention.

I just realized you have a 302 and not a 351M/400, so the choke heat exchanger is probably different on your engine.

Now I'm afraid I can't help you very much because I'm not that familiar with the 302's configuration.

All I can offer is some general info. If you have a tube connected to the choke housing and something else, hopefully that "something else" is a heat exchanger. I've seen some 302s that appeared to have a heat exchanger down on the right side exhaust manifold.

Filtered air has to have a way to get into the heat exchanger from a source inside the air cleaner filter element.

If the engine was "modified" by a previous owner, the inlet tube hole in the heat exchanger may have been plugged off with a bolt or putty, and with an accumulation of grime or rust over the years, it could be difficult to find.

Another possibility is that the choke housing tube is not even connected to a heat exchanger, but a vacuum port on the manifold. In that case, manifold vacuum would actually pull air backwards, from the venturi out through the choke housing, and the choke's bimetallic thermostat would be gummed up by residue of the fuel/air mixture that was puilled through the choke housing.

 

Finally found it! It was rusted over but now it's reemed out and ready to go. Thanks a lot for the pics and advice.

Jim

 

On my 302 the heat exchanger is in the rear of the right side exhaust manifold. The fresh air side comes into the bottom of the manifold and the hot side comes out the top. At some point in time the fresh air side on mine was removed so I don't have a filtered source of air going to the choke. Gotta work on that sometime.