Yamaha 60HP Outboard Low RPM Misfire Troubles

AUME2010

Recruit
Joined
Apr 11, 2011
Messages
1
We bought this engine brand new at a dealer in 04' I believe it was. 60TLRC Yamaha 2 Stroke 3 Cylinder. It has not run properly since the day it was installed on the boat. As far as hours run it is barely out of break in. It will misfire at idle to about 1500 or so, after that it smooths out and runs great. You can see the motor shaking like crazy at idle and hear it trying to smooth out and then it misfires and goes rough again. Hooking up a good tach to it you can watch the RPMs surge above and below 800 before and after it misfires. The dealers jacked us around until the warranty ran out and now i've sent it to 2 boat mechanics aside from fighting it at least once a year on my own to no result. We even sent it to Yamaha's "master mechanic" for our region and he didn't do anything. Ive tried cleaning/vatting the carbs and replacing seals/seats/valves etc. in them. Ive got a case of spark plugs from swapping them in & out. I drilled/pulled the brass plugs over the idle air screws and tried adjusting them. Oddly enough the #2 carb air adjust was run down onto the seat so ive always assumed a problem on it. In addition the #2 plug develops a noticeably different fouling pattern on it than the others. New enrichment valve diaphragm/gaskets. This year I checked and adjusted the lengths of every link in the throttle linkage and resynchronized the carbs and started running 100% Gasoline. I'm about out of ideas and probably going to pull the reed valves tomorrow and have a look at them. Anyone got a better idea?

Thanks in advance for any and all suggestions.
 
Top