Hi MM and Norm
went through the carb minutely many times, couldn't find anything wrong until noticed the O-ring between float bowl flange and carb body was distorted, almost severed . It was a very thin section O-ring, couldn't find anything in my extensive selection to match so gave it some TLC and managed to "de-distort" the crushed section.
Mower then started and has been running perfectly since. Seems it was sucking air through the distorted bit enough to prevent fuel being sucked into the idle and main jet.
I would say the fuel bowl o ring being damaged won't make any difference to the way a lawn mower engine will run because the carby already
has a breather where the top of the fuel is vented to atmosphere .
The only way I could see a damaged o ring on the top of the fuel bowl making any difference to the way the motor runs would be if the
air vent was metered.
In a lawn mower carburetor, the breather or air vent that allows air to enter the fuel bowl is typically not considered a metered air vent.
A metered air vent would be designed to regulate the amount of air that enters based on specific criteria, which is more akin to how certain components in more complex carburetors operate. In a standard lawn mower carburetor, the vent simply allows air to enter the fuel bowl to replace the fuel as it is drawn into the engine, ensuring proper fuel flow without any specific metering.
I've had a lot of mowers where they have a slight carby blockage and they just fix themselves ,Dirt or debris in the carburetor can lead to poor fuel flow, causing hard starting and rough operation. Once the engine runs for a bit, the vibrations can sometimes help loosen debris, allowing for improved fuel flow.
Also had a few mowers with damaged o rings on the top of the fuel bowl and it didn't make any difference to how the motor ran but
the fuel bowl would leak a little fuel when the mowers on an angle.or the mower goes over a big corrugation.
Cheers
Max.
