RPM limiter on HondaBF50?

I have a 15 foot warrior fast fisher with a honda bf50 on the back. I have never had any problems with this engine but tonight, on my way back from fishing, the engine throttled up and then seem to limit itself to 4500 rpm. It then cycled between 5000/4500 rpm. I throttled back to 4000 rpm and had no additional problems trolling home. Could this be a fuel problem, or is there a limiter to protect the engine. Cooling water stream was normal and all lights normal. On inspection i noticed the transom angle adjustment pin had sheared. Could this be a cause or coincidence? The engine has done less than two hours since service at the beginning of season.
Thanks for your help,

Jez

Yes, extreme negative trim will keep your rpms down. Replace your adjusting pin then give it another test.

You mention rpm limiter. The rev limiter does not kick in until somewhere around 6300- 6400 rpm or so.

Mike