Yamaha 9.9 4 stoke stalling

The 9.9 stalls, usually after running a while. It is like the key was turned off. It usually starts right back up. I also get changes in RPM with no change in throttle. Sometimes it starts chugging and then starts running normally again.

I have rebuilt the carborator and soaked in carb cleaning solution. I have installed a new fuel pump, changed fuel lines and put in a new fuel tank (the vent is open). The fuel is new and I filter it during refueling. The filter on the engine is new and I have checked it for plugging.

I have heard that a bad oil pressure switch can initiate engine RPM changes. Could this be the cause? Would this shut the engine down?

I really need some advice as I can't trust using the motor any more. Any other ideas I can try? I have had the engine in twice and they don't seem to duplicate the issues.

Thanks- I have had the carb off a couple of times and blown out the jets. I still may have to check this again. However I stumbled upon the fact that vapor locking can cause similar problems. Fortunately when I got the replacement fuel pump, the pump had two extra hose fittings which baffled me at first. I have since found out that this is for water cooling the fuel pump to prevent vapor lock. This feature has been included on some newer Yamaha engines. I have hooked up the water connections and will find out if this is the answer. Anyone else heard about or experienced this?