Engine is a 1986 Johnson 150 HP outboard. The motor is on a 1986 Boston Whaler Outrage 18.<br /><br />The problem I encountered, on my initial shakedown run last season, was an occasional loss of power when accelerating. For example, on occasion the RPMS would drop off dramatically upon acceleration, but when I would pull back on the throttle and accelerate again, the problem would go away, and the engine would perform fine. The engine historically, and even with this bogging problem could be trimmed out, with just me in it, to run at 5400 rpm and 47 mph (paddle wheel for reference speed only). <br /><br />When back home (70 miles from water) I then added some Waterzorb, replaced the Racor fuel water separator, and replaced and moved the primer bulb from a horizontal to a vertical orientation since that is something I wanted to change. Prior to splashing the boat again for the summer, I asked my mechanic to take a quick look at the engine to insure nothing was dramatically wrong. He performed his examination in a dyno tank and informed me that the engine was occasionally dropping a cylinder. Therefore, he replaced one of the power packs.<br /><br />Upon splashing the boat for the summer, I accelerated to wide open throttle only to discover that wide open throttle now produced only 4800 RPMs and a top speed of 38 mph (via paddle wheel). Other than that, the boat seemed to accelerate normally onto plane (no bogging as described above), but just didnt have the top end 5400 RPMs.<br /><br />I took the motor back into the shop and explained that after the replacement of the power pack the max RPM at WOT is now only 4800 RPM vs. the historical 5400 RPM. The only thing they could find was the compression of one cylinder running approximately 15 psi below the other 5 cylinders.<br /><br />Im having a tough time accepting that this 600 RPM loss can be attributed to one cylinder reading 10 to 15 psi below the other five cylinders (although I realize this is not good). The change in RPMs coincided with the replacement of the powerpack. In addition, Im wandering whether the initial run bogging problem was simply first run old fuel or water in fuel problems. Does anyone have any thoughts on what I should have looked at next? Is there any chance the powerpack was wired improperly? Is there possibly a problem with the timer base or trigger? Is the engine carboned up? I believe I only have about 60 hours on the engine since I last decarboned the engine. Im attempting to access my financial exposure with this engine.<br /><br />In a nut shell my engine initially ran at a maximum 5400 RPM and 47 MPH. After replacing one battery pack, the engine now runs at a maximum 4800 RPM and 38 MPH.<br /><br />Sorry this is long winded, but I want to insure I provide enough information.
<br /><br />Well, the powerpack could be faulty, but I think there is something else going on.<br /><br />Each cylinder on that engine has its own carb throat and jets. One may be running a bit lean because of a partially clogged jet or other problem at higher rpm, which could account for lowering compression.<br /><br />To verify which cylinder (if any) is failing to make full power you can get it on a dyno and disable each cylinder in turn. Once you have verified that it is one cylinder not pulling, you can then get into the fuel and ignition systems and troubleshoot for that cylinder.<br /><br />My money is on a carb problem. . .debris.<br /><br />Good luck. 
