You have more than 1 problem
A) The high idle points to a choke issue,like stuck on the fast-idle cam;
or possibly a vacuum leak, like a stuck-open PCV or other
B) The pocket in the fuel filter I have seen many times. Sometimes it means nothing.
There's really only three ways for that pocket to get there, and it may not be air at all.
1) the pump sucked it up; that would be air
2) it's boiling in the line; that would be gas in vapor form.
3) the fuel flashed into vapor after it came out of the pump
As to #1), Have you done the fuel pump output test yet. This will take care of proving #1
As to #2),This you can address by insulating the line and divorcing it from the engine
As to #3, this only happens if the pressure in the line to the carb drops and the fuel is hot.Like if the float valve is not sealing, or you have a fuel leak on the pressure side.
Or if the fuel is forced through a smaller hole, or over a pointy thing,
or if the fuel pump has to suck really hard on the supply line; then it will flash on the suction side into bubbles, and come thru the pump that way, and accumulate in the filter, or be forced along into the floatbowl. This could be due to a faulty tank-vent or a restricted supply line, or a kinked hose.
Usually on the pressure side, the fuel vapor will re-constitute into liquid.
But I just gotta tell you man, the pump tests are a big deal. It will tell you if the pump is making pressure, making vacuum,delivering liquid fuel or sucking air, or keeping it's prime. There is no way I would start throwing pumps at it until I did the tests. And if the tests say the pump is good, I wouldn't worry about the filter not being full. If you want it to be full; install it in a vertical part of the line , below the bottom of the float bowl. Then if it doesn't stay full, I would question it.
C) your engine may be running hotter than it should be. This may be a timing issue, a carburetion issue, a mechanical issue, or a cooling system issue.
