You should take the tank out and pressure test it. You should then replace all the fuel line with new. See if this helps the "bubbles". the main needle valve has a "clicker" on it replace it with a small length of fuel hose that seals the needle valve and keeps it from moving due to vibration. the tubing should be large enough to slip over the needle valve and the needle valve seat.
The 40 LA has an air bleed type of slow speed adjustment. this relies on air coming in through a small hole on the front of the carb, and this hole must be clean. Take the carb off and clean it carefully. before removing the carb turn the slow speed needle in until it just seats and count the turns. after cleaning Set the main needle at 1.5 turns out, and the slow speed to the original setting.

Start the engine , set throttle at the top and adjust the main needle to max rpm, set throttle at idle or slightly above and pinch the main fuel hose hard and hold and see if the rpms go up or down. if rpms go up, too rich turn the slow needle out 1/4 turn, if down turn it in. Repeat the steps above until you get a clean low idle, clean transition to high, and the best top rpm. Slightly richen the main needle before flying.

Simple huh?

No offense meant but you should have a few seasons of flying under your belt before you jump into the back of a pickup and try cross country flying.