140 Johnson surging

[Jeff Frederick]

I have a 1982, 140hp Johnson that will not maintain wide open throttle. The engine will accelerate the boat when the throttle is pushed all he way, but then it will automatically slow down to a 30-35mph cruise as if it has a governor. It will jump back up in speed and back down without touching the throttle. If you pull the throttle back some it will cruise all day at 30-35 mph with no problem. The engine doesn't miss, and it idles perfect, and starts good. We changed fuel tank lines and filters. No luck. We used a remote fuel tank setup. Same thing. We replaced the fuel pump. Same thing. Still cuts itself back to cruise speed and then accelerates up and down unless you pull the throttle back some. The carbs are opening all the way, and the boat will jump on plane when you first floor it, but will not maintain the speed. The boat is a 17' Checkmate Diplomat, and it should be easily capable of speeds of 60mph+, but we can't get it over 35! Any ideas? Thanks.