Fuel vent tube is leaking gas. The tube comes out of the bottom of the tank. When I blow air into the tube it doesn't bubble the gas in the tank and it sounds like the air is right there next to the filler opening. Why would it leak ? Would the tube in the tank possibly have a pin hole?

This sounds likely a badly routed fuel line that is getting hot and causing airlocks. The fuel delivery is slow, the gas heats up and vaporizes causing an air lock. You can test by removing the fuel line and with no engine running, run the contents of the fuel tank into a container. Do you have good fuel flow?

Or the float bowl isn't venting via its overflow pipe.

You don't say what kind of bike or give any other details so I will go with the obvious stuff first, I am guessing you might not ride it often or let it sit up for awhile. Gas pouring from the vent indicates that a float valve is stuck or the needle valve or seat seal has dried up and has fuel being forced around them as the fuel pump pressurizes the carbs. It is dangerous to run the engine with overflow as you could have a fire so your remedy will require you to pull the carbs to fix the problem.

There are normally two hose lines from the fuel filler that run to the tank. The larger one carries the fuel from the nozzle to the tank. The smaller one is a vent hose that allows vapors to leave the top of the tank while filling. These vapors come back to the nozzle area and can be vented and/or collected by the nozzle depending upon air pollution standards in your area. If your second hose is running to the bottom of the quarter panel, it is probably the vent hose that may not have been reconnected at the top of the tank when the fuel pump was replaced. The fuel running down there is from kickback fuel at the time the pump shuts off. The real problem is that the vent line is open on top of the tank and when the tank is full, that can allow vapors and fuel to escape out of there and it could contact hot exhaust areas - a major fire or explosion hazard. Have this inspected and repaired IMMEDIATELY.

Sounds like vent tube on filler neck.

Pull the spark plug wire to make sure the engine doesn't start. First check the line from the gas tank to the pump. Disconnect the fuel line from the gas tank at the fuel pump. Take off your gas tank fill cap and using light air pressure, blow into the line to see if you get bubbles in the gas tank. Canned air for cleaning computers or compressed air at a very low setting work well for this. Do not use high pressure so you don't burst the line or blow it off a connection that's not easy to get at. If no bubbles come up in the tank, check the line and pickup area of the tank. If the line is clear, reconnect everything. Disconnect the fuel line at the carburator. Holding the end of the fuel line in a small jar, turn the motor over. If the pump is OK it should shoot gas into the jar. If not the pump should be replaced. If it does check your float and needle valve in the carburator bowl.

Its leaking from the tank?
You might need some new tubing.
If there is a hole in the tank try to find it and use putty/epoxy to seal it.
This is a simple leak, there is no need for an entire new fuel system

Vent tube runs parallel with filler tube, blow it out with compressed air.

Be sure to not overfill the tank. Just load it with gas up to the bottom of the neck and be positive you're not cross-threading the cap when twisting it on. If it only leaks when operating, see if there is fuel bubbling out through the vent(s) in the top of the cap or out from under it. Also wipe the tank clean and dry to be positive it is not leaking from a seam or crack in tank or around fuel lines. If leaking from cap, might have to replace as they do have an internal rubber seal that could have gotten dry or cracked. If it's from the tank seams or fuel lines replacement may be neccessary of either one or both.

where the filler neck goes to tank didnt it have seperate tube which is vent or with filler neck hose off at tank look inside tube for another hose it is vent hose take fuel cap off and blow air from tank end towards the filler cap area we have had two ford vehicles lately in our shop when we blow shop air backwards thru hose several little round pieces of foil off of fuel injector cleaner bottles somehow they had become lodged in vent line and one customer had vehicle towed from gas station because they were on empty and would accept no gas you may want to check this doesn,t have to be cleaner bottle tops could be any sort of debris but ours came flying out of fuel cap when when blew air thru you could pump gas with handle all the way down she was happy