Re: 2001 Mercury 125 saltwater series Help!
The first thing you should do is get a manufactures service manual for the motor so while working on it you can look up most every answer if you have a question while doing the work. He is a link to a online manual for your motor;
Boatinfo - Mercury Service Manual for 75--90-100-115-125 hp
A manufactures manual can be bought at most dealers or by going to Mercur Marine online and contacting them for one. The main reason I recommend the manual is because there are several things that can cause your trouble and they need to be checked over one system at a time. A compression test should be one that is done first and then you can move on to the others, electrical then fuel. If the compression is good then a spark test should be next. It could be a bad switchbox ,stator, triger, or a few others causing the trouble.
Sometimes it is best to cheaper and easier to take it to a dealer with factory certified tech as they have the equipment to hook up to a program on a computor and it will tell just what is causing the trouble. The newer motors are equipited with a ECM, much like the new cars are today. Not sure if yours is but there is a possiabilty that it is. JMO
Oldman570