7.4 mark IV inboard muffler question

BigJoeB

Member
Jul 25, 2012
177
Staten island, New York
Boat Info
1992 Sea Ray Amberjack 310 with Tuna Tower Mod. Great Boat
Engines
Twin 7.4 Mercs.. Thirsty Girls
hello everyone,

Have the boat 3 years never had this issue . Does the mufflers have check valves inside? Cylinder #7 was hydro locked a few times. Changed risers, still happens. Lowered muffler still happens, and only happens when boat stops after a nice run. I let it idle for a while and still happens . It does not happen when in the slip running. No water in oil at all. I drain cylinder, spray some stuff in it to lube plug and white back and starts up no issue. So, I am wondering if there is a check valve or flap that is not working that is inside the muffler. So I know what to repair lol
Thank me all
Joe
 
If you have a merc outdrive, there are flappers in the exhaust Y pipe. Sounds like a manifold issue. Were they replaced when you did the risers?
 

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