rpm surge

So I'm pretty new to this so bear with me. My XP 2001 runs at about 6400rpm, When i flush the coolant system, 1 minute 5 minutes doesn't make a difference and start up in the water (engine already hot from the flushing) it stays plus 7100rpm for about 2-3 seconds then drops back to 6400...

55 hrs, new plugs. just above idle runs rough with alot of surging until about 1/3 throttle, then runs fine with good power. Tach does not work, so I can't give exact rpm. Any ideas? thanks.