by Vance
(Hawaii)
I have twin Yamaha 40hp 4 stroke Model F40TLRY on my boat. The engines idle fine but on one of the when I get it up to trolling speed (3000 rpm) it is great for some time but after it starts to miss and it does not die. I put it back to neutral and it idle fine. I play around with the controls and then it start to run fine for a time period and starts again. I've switched the coil/spark plugs/fuel pump/carbs/stator/Rectifier/regulator/CDI from the good engine to the bad one and it still happens. Also I've switched the external fuel lines from the good engine to the bad one and it still happens. I don't know what to do. Does anyone know what small thing that I haven't check yet. Thanks.