Lost 10 mph...HELP

[Mod VP]

This is my 1st outboard,so bear with me.When I bought it (19 ft. Laveycraft/Merc 150 XR4)it went 75 to 78 mph.For the last 2 summers it won't go over 65 mph at 5500 rpms.The only possibilities I know of are I've added a set of 4 speakers,and a amp(mounted in proximity of front seats and an amp)And it started to overheat in the driveway once.The damn water attachment rattled off the lower case.Anyone know what I can check ???? Thanks

[snappertapper]

check the compression and take out the thermostat or try a smaller prop
email me with any questions bigfish1229@aol.com

[mercmancolo]

Have you pulled the spark plugs and looked at them? If one is very clean you may have lost spark on one cly. and have a bad switch box.

[cavey lavey]

if it overheated badly you may have fried the water pumpgear. disconnect the power lead to any new electronics and set the motor where you run it at your top speed before you take off watch your rrrrs rpm if no change snappers right you have lost some compression, good luck.