That is what is called a vacuum tree. The large connection is for the power brake booster. One smaller one is for the transmission modulator and the third one is for the air conditioner.
On an engine bolted to the intake manifold.
The intake is the tube that attaches to the engine - usually the carburetor is attached at the opposite end of the tube (intake).
You have to get a special intake that you can bolt a carburetor to.
Gravity and vacuum. The air flow into the engine creates a vacuum that sucks the metered fuel from the carburetor into the intake manifold and from there through the intake valves into the combustion chamber where it is ignited by the spark plugs.
I think you will find that this truck is fuel injected and has no carburetor. If I am wrong and it has a carburetor it is mounted on top of the engine dead center on the intake manifold.
Front of the engine, under the intake and behind the ac compressor.Front of the engine, under the intake and behind the ac compressor.
There should be a vacuum port on the back of the intake, behind the carburetor. It has to have vacuum on it at all times.
It is a vacuum tree. One line will be for the transmission modulator, One is for the Air Conditioner reservior tank and the last is the vacuum sensor in the thermostat housing.
the carburetor or the fuel pump this takes place in the intake manifold
There is no carburetor located on a 1994 Nissan Altima because it uses fuel injection. A carburetor is typically located on top of the engine on the intake manifold.
I person needs to have a diagram when making any changes to a car. For a Nissan Sunny B12 the diagram to the air hoses connected to the intake manifold and carburetor can be found in the maintenance manual.
Normally from an engine backfire. The plug fires when the intake valve is partially open which will explode the fuel in the intake and carb.