RE: ys f-120 (messy?)
First off there is a YS forum in the glow engine forum with answers to most any question you may have about these engines. A lot of information. If you have sprung a leak in any of the lines or have a bung problem it is easy to spot right after landing/running. If you don't get pressure from your pressure line it's a dead give away. If anything the YS is a cleaner running engine then any of the other four strokes. If you are getting fuel splashing out of the carb then your not tuned correctly. All these things are covered in the YS forum. The YS pumps about 7 pounds of pressure into the fuel tank so as John pointed out, any hole or loose bung will squirt fuel.