Re: 115 hp
First thing to check is for adequate spark, use or make an adjustable gap spark tester set to 7/16 inch, you should have a hot bright blue 'crack' on ALL cyl's.
Most ignitions have a minimum cranking speed of 300 RPM, it takes a good battery and CLEAN connections on all cables on BOTH ends.
Merc made a number of 115 models, 4 and 6 cyl with different ignitions throughout the years, your serial # would really help us to determine exactly what you are working on.
