89 Mercury 15 hp Running Rough

[Harbicide]

I have an 89 Mercury 15 hp that is running rough. From Crowley drawings it looks like there is no head gasket in the motor. Could it be the deteriorated exhaust baffle gasket is causing the rough running?

 

[racerone]

Exhaust passage ways could be plugged with carbon.----Was this " rough running " a sudden event ?----Changed the water pump impeller recently or never ?

 

[fastjeff]

No head gasket on that motor.

Jeff

 

[Harbicide]

Yes it was sudden last weekend. The impeller was changed 2 years ago and still looks OK. Looking on top of the pistons is a black oily substance. I did add SeaFoam to the tank at the amount of 2oz/gallon before the weekend.

 

[racerone]

Do a compression test.-----Check flywheel key.----Check fuel pump diaphragm .----Check carburetor float ( filled with fuel due to a crack ) and motor flooding.---Check for spark on both leads.---Strong spark can easily jump a gap of 3/8" ( 1 cm ) on that motor.