costarican pilot,

All the above info & hints are true. Try and convince yourself to take nothing for granted. The root cause can be a simple issue like too large a size silicone tubing. The connection of the tubing to the carburetor if it is too large, air may leak in to the fuel line and cause bubbles. Make sure the fitting on the carburetor is tight, also check your exhaust pressure line inside the tank, it should be bent towawrd the top of the tank. If it is bent the wrong way (downward for example) it will bubble & foam into the fuel tank. This last one is a bit of a push, but check it anyway after you follow the advice above you will fid it. Be patient, and be determined to not assume anything is Ok unless you check first.

Sledge_78