whats the easiest way to tell...

[dfrants]

whats the easiest way to tell if you have a scored cylinder(s)? today as i was going across the lake, at about 3/4 throttle, my 1999 125hp merc slowed down like it was running out of gas. i shut it off to see what happened. still had gas, the overheat buzzer didn't buzz, i had good water pressure the whole time. got back to the dock and checked the plugs. the top 2 look fine, number 3 looked a little gray on part of it, and the bottom plug was grey and dry. a compression check showed 120-125psi on all 4. put in a new set of plugs and she started and seems to run ok. i'm worried what could have happened and don't want it to happen again...

 

[CharlieB]

Re: whats the easiest way to tell...

The motor can be running out of gas. The fuel pump may be dying, air sucking into the fuel system, dirty carbs. Any one or a combination will cause a loss of power, leaning one or more cyls and melting a piston.

This 'grey' on the spark plugs is a sign of a serious lean burn. Shortly after that your would be seeing little grey splatters of molten aluminum piston.

Order carb kits and clean your carbs, a fuel pump rebuild kit. Once finished use a temporary clear hose in place of one of the hoses from the fuel pump to the carbs, run the motor and watch for air bubbles passing thru, indicating air sucking into the hoses anywhere in front of the fuel pump to the fuel tank.

Be sure to remove that clear hose once finished as it is NOT approved for fuel use, only for short term testing.

You may have gotten very lucky, this time. Don't push it.

f you want to inspect the cyls you can remove the exhaust side covers and look in thru the exhaust ports. Be very careful, the exhaust bolts have a nasty habit of siezing and breaking off if you just put a wrench on and yank on it. They have to be gently coaxed to turn and come out.