1987 classic 50 MERCURY 45 HP 4CYL NO POWER

[pthotts]

WE CHANGED PLUGS/FUEL PUMP / REBUILT CARBS /NEW FUEL LINES.
THE MOTORS STARTS AND RUNS GREAT OUT OF THE WATER . THERE IS A GOOD STREAM OF WATER FROM THE IMPELLER. ENGINE JUST GETS WARM AFTER SEVERAL MINUTES OF RUNNING
WHEN WE PUT IT IN THE WATER IT HAS NO POWER, WON'T REV MUCH PAST HIGH IDLE.
COULD IT BE THE LOWER UNIT? BEARING?

 

[racerone]

Trouble shooting is required.-----------Compression test is # 1 item to do.---------Then look for strong spark on all leads.----------------Strong spark is not a spark that can jump the gap on a sparkplug.--------It is strong when it jumps a gap of 3/8" or more.---------------Also check exhaust tuner is not plugged up.-------------Is this problem something that showed up suddenly ?

 

[pthotts]

OK BUT WHAT IS A EXHAUST TUNER AND WHERE IS IT

 

[pthotts]

YES IT SHOWED UP SUDDENLY