Ok guys a little backgroud first, I have 15 years experience with automotive engines and applications, that being said I have only owned two boats. one is a 10 ft. SeaKing all fiberglass hull with a Mercury 25 Hp. outboard, this how ever is not the boat in question. The subject of this thread is a 1976 Arro 18 Ft., walkthrough windshield, 165 Hp. inline 6 Mercruiser with the I drive, pre alpha as I understand it. the serial number for the engine is 3692675 and the stern drive is 33216833. Some background on the boat, when i bought it the motor had everything taken off right down to the block everything was scattered out in the floor of the boat. Was told the block had a crack in it. Upon inspection I found a fine hairline crack about 1 1/2 inches long on the water jacket side between the first and secound freeze plugs and the third had been tilted out of its hole. Decided it was from freeze damage due to improper layup for the winter where the previous owner either forgot or did not know how to drain the block properly. Took the motor to a local head shop and they pinned the crack for me, I don't know if any of you guys have had sucess with pining block cracks but I have never had a problem with it in the past. Fortunately for me the previous owner labled everything when he dissasembled the moter right down to the nuts and blots and where they came from. after 3 hours of re-assembly and a carb rebuild and new points that where provided I had her up and running rough ideal at first but running. read the shop manuel and reset the idel screws at three turns each shes' still a little rough but idels at 700 RPM. Took her to the water today and ran her up a little. From what I understand this motor tops out around 4500 to 5000 RPM under load. On the trailer and in a tub of water the engine ran up stead as a rock to 5000 RPM still with a slight miss at idle. When I tried her out with five passengers she would barely make 3000 to 4000 RPM. She did manage to plane out but would not get over 3000 RPM after that. Noticed the bilge taking on water and the pump kept up with the leak and we ran her for about an hour or so. Once we got her back on the trailer and home I checked the stern drive for possible leaks and found that the drive shaft bellows (not sure what it's called) had two cracks in it on the left side so that needs replacing. Any ideas as to what is causing the lack of reaching max RPM and what might be causing the rough idel problem as well. I tried to be as through as possible any other information you might need to help with the diagnoses let me know. Thanks.
