9.9 Yamaha misfiring

[Bob G]

The motor runs great and then suddenly starts to misfire. This can go on for 5-10 minutes and suddenly runs fine. It appears to be starving for fuel. This usually happens after the motor is warm. The fuel bulb is usually soft but pumping it doesn't seem to help.
The carborator has been cleaned by a mechanic, the fuel hoses have been changed, the vent is open(have even removed tank cap to eliminate possibility of tank vacuum). The fuel filter is clean. Has anyone got any other ideas. I can't trust the engine and am even considering buying a new engine. Thanks for any ideas.

[boats.net]

Make sure has the correct spark plugs in it and check spark plug cap's(resistor plug caps will cause a misfire if bad)