old 90hp 2/stroke power pack problem

[captain rednut]

hi i have a 90hp 1988 model 3cylinder yamaha 2/stroke that has repeatedly grabbed no 2 piston, the engine had a 40 thou over piston in the middle cylinder which failed when my customer bought his boat and we have changed the power head and its done it again, it has the old screw type ignition power pack which i have been told by a local outboard wrecker that these power packs can cause this and he has seen it many times?? he believes the pack changes the timing on the middle cylinder only, has anyone ever had this before?? as i will check the timing on all three cylinders next time but would like to know your thoughts.
regards jim

[boats.net]

The CDI is a small part in timing, the three pulsor coils, flywheel, timer base and adjustment is the main components in timing. Need to try and determine if it's a preignition or detonation problem.

[captain rednut]

thanks for your reply