1998 150 EFI
New member
My 1998 Merc 150 EFI has 350+ total hours. It is mounted on a 22 foot tritoon, and has run great until a few weeks ago. At full throttle, with one person on board, it would run about 30 mph. Three weeks ago, it started missing badly at all throttle settings, from idle to WOT. I replaced the ignition trigger assembly with JETUNIT aftermarket unit. The motor runs strong now with no missing, but it will not reach full rpm at wot until I touch the trim button. With the throttle lever full forward, it runs well, but not at wot. As soon as the trim switch is touched (up or down), the motor immediately increases to full throttle. My tach is not working, so I am going strictly by sound level and speed, but I would estimate I am gaining roughly 3-4 mph when I activate the trim. This happens instantly, not because of any change in the angle of attack of the motor. It has to be some kind of electrical issue. I have checked the battery connections, and any ground I can find on the motor, but everything seems clean and tight.
I have a video I took last weekend that shows what is happening -
It is hard to hear anything at first because of wind noise, but toward the end of the video, I moved the phone down closer to the throttle and you can hear the engine speed up as I touch the trim. I am open to any suggestions or ideas.
Thanks for your assistance, John
I have a video I took last weekend that shows what is happening -
Thanks for your assistance, John