Carburetor flooding — black smoke and rich mixture

Engine runs extremely rich with black smoke from exhaust. Strong petrol smell. In severe cases fuel may be visible dripping from carburetors. The Zenith 35/40 INAT uses a needle valve and float system that can fail with age.

• Black smoke from exhaust
• strong petrol smell
• fuel dripping from carburetors
• engine runs roughly rich
• spark plugs black and sooty

• Worn or stuck float chamber needle valve
• incorrect float level
• perished float
• stuck float
• faulty accelerator pump check valve

1. Remove carb top.
2. Check float level — should be 14-15mm from gasket face.
3. Test needle valve for leakage.
4. Shake float and listen for fuel inside.
5. Replace float or needle valve as needed.

Replace needle valve and seat. Adjust float level to specification. Replace float if fuel-logged.

Zenith 35/40 INAT needle valve set; float assembly