I have a 1985 Merc 115 in-line 6 with a problem that has been growing increasingly worse. <br /><br />At low RPMs (less than 2000) the motor seems to run fine. The problem occurs when I try to get out of the hole.<br /><br />Previously, when I'd engage the forward gear and start off under a load (the hole shot) the motor would run sluggish. After running for about 10-20 seconds at 1/2+ throttle, the motor seemed to spring to life, like a few cylinders woke up, and it would take off providing substantially more power.<br /><br />More recently, when I engage the forward gear and start off under load (1/2+ throttle), the motor continues to feel sluggish and no longer has that 'spring to life' effect. As well, I am maxing out at 2800 RPMs at WOT! Motor also seems to sound louder.<br /><br />It still seems to run fairly smooth at low RPMs. However, 7 MPH isn't much fun.<br /><br />I've rebuilt the fuel pump and checked the lines for air leaks. As well, a marine mechanic checked the spark (using the plug extensions with an in-line indicator light)...all seems well. I've also cleaned the plugs, yet problem still persists. 
<br /><br />In the 3 years I have owned the motor I have never 'decarbonized' it. I am using clean gas and good oil (50:1). I always put it to bed in the winter by running out of gas and using fogging oil.<br /><br />Would appreciate any assistance/direction you could provide.
<br /><br />In the 3 years I have owned the motor I have never 'decarbonized' it. I am using clean gas and good oil (50:1). I always put it to bed in the winter by running out of gas and using fogging oil.<br /><br />Would appreciate any assistance/direction you could provide.