800s low tach after running hard

[switt]

Have challenger 1800 with twin 787 rotax. Ran it about 6-7K rpm, full throttle, for about 20 mins. Stopped and when restarted, neither engine would tach above 3-4K. Opened back and the heads and pipes were warm, but not hot, to touch. However, a drop of water on the lower end of engine sizzled. Idled for awhile and never got the rpms back before getting to dock. Compression in all cylinders are 135ish. Does the MPEM cut back rpms when hot? Curiously, the temp sensors are in the heads which were only warm to touch. Dont know what to expect next time out.