I have a 555 with 610 HP. It has been performing great, but recently I seem to have lost about 150 rpms. Weather seems to be about the same. Any thoughts what might be causing this? Still seems to be running great though. Bottom of boat is clean. I know this is wide open and not a lot of info but I am wondering if anyone has any thoughts on what might just change. The engine has about 10 hours on it since building. It is a carb engine.

A few things that I would start with is first check the prop to make sure you didn't ding it or possibly bend a blade. Otherwise as far as the engine goes I would change the fuel filter, check timing, make sure no plug wires are shorting out against the engine and or accessories. Also be sure and check your valve lash. You may have already started the above however they just popped to mind. Be sure and let us know what you find. I would assume your speed has dropped as well to rule out the tach being off????

Good luck!
John

Thanks for the suggestions. My GPS speedo is out. Probably the battery. I will need to check it with the hand held. Prop looks good. I will switch out the filter and check the wires.