Outboard trouble!!!!

Trying to figure this one out.  As I was coming back in yesterday my motor was running around 4500 rpm's, then it dropped down to 4000 rpm and sounded like it was struggling then died completely.  I started it back up and right away it went 7000 rpms at idle and when I turned the key to off the motor kept running.  I tried the kill switch and turning the batteries off, but it took disconnecting the fuel line to shut the motor down. I tried started it up a few minutes later and it started a little more normal but died off as soon as I put it in gear. Limped in the rest of the way on my kicker and I tried again in the harbor to start the motor and it jumped to an insanely high rpms right away and stayed, but this time shut off when I turned the key off.  The motor is an 89 johnson 70hp... does anyone have any idea what could have caused this behavior?  I had a problem with this motor just not starting earlier in the season but I got that figure out and it has been running fine.  
 
Thanks

The throttle was in neutral, and it hit 7000 rpm on the tach(the max my tach reads). All of the spark plugs and spark plug wires were replaced this year.

If it;s a 2 stroke sounds like it may be an air leak. Could be carb,crankshaft seals,may be able to pressurize through carb and listen?

Power Pack = Not Cheap
 
Hope this fixes it up for you, update again after you run it several times. Glad you got it going again, nothing as frustrating as those types of issues...