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Collection, Preservation and Display of Old Lawn Mowers

Air in fuel line

Early 90s Qualcast 35s.  Given it a good clean and stripped and cleaned the carb. New fuel line and filter. Head off and cleaned because the gasket was blown.

Now after a few minutes running I'm getting air back up the fuel line from the carb. I thought vapour lock but there's an awful lot of air coming back and the engine keeps stalling.. Could it just be a poorly seated fuel line letting air in, it looks OK.

There's an idle screw on top of the carb but I'm not 100% certain whether I need it slightly in or out. Any thoughts?


wristpin Sat, 02/06/2018

Air in the fuel line is a bit of a strange phenomenon and not necessarily detrimental to running.  Modern BS Vanguard and Intek engines with clear fuel filters often appear to have only half full filters yet are performing correctly. If the engine is running OK I wouldn't worry about it.

If your query about the idle jet setting refers to a Zenith carburettor , around half to three-quarters of a turn from fully closed is usually about right.