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fall 2004: 800 hours on engine; plugs changed every 50 hours, ring free added every fill up. Engine started losing RPM while at cruise speed, about 4200 rpm. Eventually problem became losing rpm at all speeds...then hard to start...then No start. Local yamaha mechanic blew out fuel lines, replaced primer bulb, O2 sensor and cleaned injectors... Problem went away until this week. 40 more hours on motor since inital problem. First hint...stalled at idle in neutral. Now back to same problem as before losing rpm at almost any speed: idle, *****ing, cruising, hi speed. Loss of rpm may, after lots of engine lugging, return to "normal" or continue to "lug" until engine stalls and then either becomes hard to start or won't start. If enough time passes...engine will start again fine and show no problems until after it has run for several minutes. One day this week it took a full hour before the problem returned. Today, it was back almost immediately. We have: charged and checked batteries, drained fuel and checked fuel tanks for "debris", replaced fuel filters, drained VSC tank, replaced plugs and tested fuel pressure...none of these actions indicate a problem or have corrected the problem, in fact it is continually getting worse. Same local yamaha mechanic road in boat with us and boat exhibited loss of rpm....but he said it would have to get a "whole lot worse" before it could be diagnosed. He was convinced it was a fuel problem...however...all of our efforts indicate otherwise...ANY IDEAS?
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Lizzard,
Seems you have covered the area of fuel delivery - I'm kinda thinking maybe CDI unit. I say this because my fishing buddy had a very similiar problem with his C115 - couldn't really pin down any pattern as to when the motor would start acting up - I guessed it was a thermal problem with the electronics of the CDI. Pretty expensive item to replace just to see if that is the problem, though.
Good luck,
Ken K
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