1996 115 merc

[clark fowler]

This 115 merc runs on 2 carbs at idle.also called a 2 plus 2 I think.Anyway in driveway warmed up the motor will start to idle up to around 1500 rpm then a little back fire (pop) puff of smoke rpm drops to about 700 rpm then idle to 1000-1100 rpm for a bit then do the same thing over again.Anyone have any ideas.when Im out running it on the water runs good.planning to go run on lake wednesday to see how it goes. thanks for any advice Clark

 

[achris]

Re: 1996 115 merc

The 2 plus 2 systems shuts down the bottom 2 cylinders by leaning out the mixture until it is too lean to fire. The point the bottom 2 cylinders start to richen up is about 1500-1800 rpm. I believe what you're experiencing is the mixture becoming richen enough to fire, but not accurately, so you're getting a back-fire. That's causing the engine to bog down and slowly start to build the speed again...

Check that your idle speed, in the water in forward gear with no impediment to the boat moving, is 650-700rpm... It wouldn't surprise me to find your idle speed is way too high...

Chris...