Fuel systems don’t get the glamour of engines or gear, but a poorly specified or poorly plumbed tank causes more mysterious “engine problems” than almost any other single component.
Size for your typical flight duration, with margin. Running a tank close to empty regularly isn’t just inconvenient — it increases the chance of uneven fuel pickup and air getting into the line as the fuel level drops and sloshes with manoeuvres, which shows up as intermittent lean running or cutting out, often blamed on the engine rather than the fuel system.
Placement affects feed consistency through the flight envelope. A tank mounted too far from the engine’s ideal fuel level, or positioned so that aerobatic manoeuvres regularly uncover the pickup, will cause exactly the kind of intermittent fuel starvation that’s maddening to diagnose in the field. Following the airframe designer’s recommended tank position (rather than fitting the largest tank that physically squeezes in) avoids most of this entirely.
Clunk placement and free movement matter as much as tank size. A clunk that’s snagged, kinked, or restricted in its movement inside the tank defeats the purpose of having one at all — it’s worth a visual check (tank empty, clunk moving freely through its full range) whenever you’re setting up a new tank or troubleshooting inconsistent running.
Fuel line condition degrades gradually and easily gets overlooked. Silicone fuel line can harden and crack over time, particularly with petrol rather than glow fuel, and a line that looks fine but has lost flexibility is a common, easily-missed cause of intermittent air leaks into the fuel system.
A full fuel system check belongs in the same pre-season routine as gear and fasteners (see Days 14, 15, and 17) — it’s an unglamorous job, but fuel system issues are among the most common causes of in-flight engine problems that have nothing to do with the engine itself.
Our Petrol conversion fuel tank bung and fittings is a good reference point if you’re shopping around.