Stalling Motor at higher Revs

[dougd1]

I have a 9.9 hp 2006 Mercury OB motor. When I am running the motor at higher revs, it will "stutter" or simply completely stop. No problem restarting it, but am wondering what would cause it to suddenly stop like that. Any ideas or things to check? My fuel tank is equipped with a fuel hose that has a fuel demand valve fitted, although I operate the tank with the tank vent opened.
Any help appreciated.

Doug

 

[airshot]

Check fuel filters, if there are none, add one !! Water in fuel ?? Crud in fuel or fuel line. Not sure what a fuel demand valve is...

 

[dougd1]

Fuel tank was emptied last fall and filled this spring with premium fuel. Fuel filter is fitted, but no way of checking its condition that I am aware of. Engine shutting off only happens at higher fuel flow rates.
Fuel demand valve is the valve in the tank fuel line that prevents overpressurization of the fuel line when ventless tanks expand in the sun and increase the fuel line pressure in the fuel line to the engine.