This summer my 2005, 50 hp Mercury 2 stroke began to sporadically lose power at random while traveling at WOT, up on plane.. The motor did not cough, sputter, hesitate or need restarting. I then would give it WOT and I'd be right back up on plane. After about 6 hours of engine use, this pattern changed to when going WOT: the motor ALWAYS "bogged down" and would not go up on plane.
The entire time, my Mercury always started fine, idled fine, and ran smoothly at fast idle in forward.
Diagnosis.
In the driveway, at idle and using an inexpensive "Inline Spark Checker," I found NO spark at cylinder #3.
Following the exact CDI Electronics Diagnostics Troubleshooting for my Mercury motor by year, hp, number of cylinders, using CDM Modules--I continued following the diagnostics for "One or more Cylinders No Spark." Through this simple inline spark testing,I was able to determine the Trigger component was bad and needed replacing.
(The trigger sits under the flywheel and sends a lo voltage signal to each CDM module signalling to release the voltage to the spark plug. The trigger provides the "timing.")
In order to access the trigger, the flywheel needs to be pulled. A puller is necessary. And to reinstall the flywheel nut at 100 ft lb of torque--you'll need to hold the flywheel fixed in place. I custom cut 2 - 2x4's strategic placed against the transom of my boat. Or a person can buy a special tool made specifically for this purpose.
My Mercury now runs full power at WOT.
CAUTION: be methodical in diagnosing whether the stator, the trigger, or one or more of the CDM's is at fault when encountering these types of coil - spark - ignition types of problems.
Thanks for all the various posts on THIS forum. I sure appreciate all the help.
