1999 Suzuki 70hp four stroke

Just bought twin 1999 Suzuki 70hp four strokes both start and run until I start to plain starboard runs well port will only rev to about 3400rpm(2500 without the help of the starboard engine) Let me also tell you what work has been done to the port engine. New fuel pump, new high pressure valve, new fuel lines, fresh fuel, new spark plugs decarbon treatment, and new fuel ball. Just had a mechanic hook up his computer to engine and nothing showing wrong or out of ordinary. He also checked fuel pressure 40psi entire time. The engine dies after 5 to 10 min of idling. I've run the engine about 15hrs at full throttle it has run at 4500rpm but only for about 30sec then back down to 3400rpm. Suzuki said put in hotter plugs and ring free in gas which was done just before a 12mile run with no change. Running out of ideas but I think its something simple the engine sounds good the entire time its running. Thanks for any suggestions