Small Engine Troubleshooting Problems? Ask a Mechanic Now.
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There are two hoses that come off of the carb. The drain hose is #23 and attaches to the bottom of the carb float bowl. The vent hose is #24 and is higher up on the main body of the carb. Can you inspect the hoses and be certain that it is the drain hose that is leaking fuel?
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If it is coming from the drain tube even when the screw is tight then there must be a problem with the sealing of the drain screw. It has a tapered end that fits into a corresponding taper in the bottom of the float bowl. You can remove the drain screw and inspect the taper and threads for any sign of damage. If good the next step would be to remove the float bowl and inspect it for corrosion, dirt or a crack in the area of the drain screw. Let me know what you find.