POTENTIAL CAUSE
1. Long idle periods.
2. Low grade fuel.
3. Fuel tank vent restricted.
4. Fuel return line restricted.
5. Engine problem (low compression excessive blow by, worn rings or valve stem seals).
CORRECTION
1. Try to avoid prolonged idling.
2. Add proper quality fuel. (not necessary to drain and refill tank).
3. Clear vent and line.
4. Clear restriction. Replace line if kinked or pinched.
5. Diagnose and repair as indicated.
