Idle Problems on 15 hp Yamaha

[Arkie1]

I have an early to mid 90's Yamaha 15hp 2-stroke that will not run at idle. It will run at 3/4 to full throttle. It will only start at almost full throttle. I have cleaned the carbuerator, thus seemingly eliminating that problem. Could it be the diaphragm? I have changed the gas, so I know it is not bad gas. Both plugs are firing at all throttle positions. I assume that this is a problem in the electrical system. Does anyone know how this system operates, and if so which one of the electrical coils would cause this problem? Is there any way of checking the coils so that I can find the bad one? When I used the boat for duck hunting this winter it was running just fine.<br /><br />Any response would help. Thanks.

 

[Boatist]

Re: Idle Problems on 15 hp Yamaha

Arkie<br />If you have spark then I think Electrical system ok. The problem you describe sounds like the low speed idle need adjusted. I do not know the Yamaha 15 but my Johnson 15 has a idle mixture adjustment knob on the front. The high speed mixture is done by a fixed jet. Check your manual for carburetor adjustments. Can you tell if running rich or lean, makes a different sound.

 

[Arkie1]

Re: Idle Problems on 15 hp Yamaha

Thanks, Boatist. I will give that a try. Unfortunately I do not have a manual for this motor. I have been hesitant to make any adjustments without knowing the normal settings. I have broken down the carbuerator again and I am letting it sit overnight in carbuerator cleaner. I am planning on putting it back together this afternoon. Do you happen to know a general rule of thumb on adjusting these carburators? <br /><br />The only weird thing about it is that it was running great when I last used it. I go to start it about 2 -3 months later and it won't start at low idle.<br /><br />I appreciate your response.