I have 19 foot jetcraft river boat w/turbojet 115 motor The motor seems to run great but between about 4,600 - 5,200 RPMs I get an intermittent noise, almost like a rock is rattling somewhere, or a bearing? when I change the rpm speed it goes away for awhile. it will sometimes go away when I raise the rpm but will always go away when I lower the rpms. It does not seem to affect the performance of the engine though. One more thing to note is I was on the river the other day and for the first 15 minutes it did not make a peep, almost like the part needed to heatup before it made the sound.<br />I recently installed the 2 high performance kits for this engine. When I got the muffler from the dealer it had a piece of casting in it that rattles they said it was fine that way, I tried to get it out but couldnt, but I belive the muffler fills with water when running? If only this is issue it would be great, but I suspect this is not it. Im afraid it is something in the engine or lower jet unit. I have tried running the engine wix mixed gas in conjunction with the oil injection to rule out not enough lubrication in the cyl. The sound will rattle for a few seconds then stop for a quite a few seconds then come back. Any ideas?
