I have a 29 foot Blackfin Flybridge with 1999 Volvo Penta 7.4GI / 300 hp twin inboard engines. At the end of this season I started hearing a banging noise in the port engine when I increase rpm to 3000. Port engine will not go more than 3000 rpms. Compression test shows low compression in one cylinder on the port engine. I need to replace exhaust manifolds and risers and investigate port engine issue. I am trying to become a DIY. Any advice, contacts or direction would be much appreciated. Thanks