Re: 1988 johnson 90hp runs great wot dies at idle
It could be a number of things. The idle timing could be too low, causing the idle to be to low. That engine should idle between 650 and 750 rpm when in gear, idling at the dock when the boat is sitting at normal level in the water. You can't set the idle on the trailer. Also, when idling, the butterflys are closed. When closed at idle the engine draws fuel from special idle circuits (passageways) in the carbs. If one of more of these passages/jets is clogged with dried fuel, it won't idle properly. Once the throttle is advanced even slightly, the butterflys will open and draw fuel from other jets for mid and high rpm operation. You might want to check the idle passages and jets again. An engine will run well on the trailer on 3 cyls. Once in the water, in gear, a dropped (missing spark) cylinder can prevent the engine from idling properly. Check the spark when the engine is idling under load.
