The Big Bopper
New member
Hello My name is Keith and I live in Kent in the UK . I own The Big Bopper Power Boat 17 Footer with a 80hp Mercury Blue Band. There is very little concrete information on the net about these motors with regards to bad running due to water in the cylinders normally the bottom one. I thought that seeing as I have totally stripped and rebuilt mine and found the fault and fixed it I would share the wealth to save any of you guys pulling your hair out with regards to where the heck all that water is coming from and why its pumping out of the spark plug holes and just how much damage can result from ignoring it. When I first purchased my motor it had been sitting for 5 years so I did the usual strip and rebuild fuel system , replace water impellor and gear box oil and start her up . After 5 minutes of cranking over it eventually started first on 1 cylinder then only 3, it ran for 5 minutes before cutting out and would not start again . so I removed the plug and was met with water soaked plugs on all cylinders. cranked over with plugs out and I could have watered the garden with the amount of water pumping out . I quickly sprayed fogging oil into the carbs and plenty down the plug holes to prevent corrosion . I decided to remove the power head as its much easier to work on the head and jackets this way . Now to the meat of this story If you have water in any of the cylinders replace the crankshaft oil seals and make sure you fit the two bottom ones with the lips FACING DOWN (really important) . Also replace the Inner water jacket gasket as this was leaking on mine and pumping water straight into the bore and washed it red rusty, also replace the exhaust baffle plate gaskets and if the middle baffle plate is corroded through then replace it as water will pump straight through and yes you've guessed it straight into the bore! the exhaust side of these particular motors is pretty poor in design so if it goes it blows your bores with lots of water. Symptoms of the above faults are missing on one or more cylinders wont rev or plane without choke being held on and cuts out when off the plane. Its worth noting that the motor will run fine on muffs or in a barrel but when the motor is in the water properly the water sits higher inside the leg so water pressure is stronger hence water jacket leaking direct into the bores. I decided to write this to help others as I spent weeks looking for this valuable information but could not find it . Check out The Big Bopper Power Boat on you tube and you will hear what she sounded like before she took out all the pistons due to more water that oil. Happy Boating from The Big Bopper:rolleyes:
