idle jumps on 86 johnson gt150

[gonefishintoday]

Hi,

Just sitting with motor idleing it will jump in rpm about 300rpm higher then back down to normal. Not consistently doing this. It appears as a random thing.

At higher rpm it does not do this.

any ideas?

thanks

[ChampioNman]

Here is something you can try at the house. Trim the motor all the way down and start it on the cooling muffs. Once the motor comes up to temp and still at idle start trimming the motor up to just past level and watch the tach and listen to the RPMs, if they level out then trim back down if it starts to jump. Replace your recirc valves and hoses. There are six of them and you will have to remove the carbs from the intake manifold to get too them. But your idle will smooth right out.