1975 Mercury 20 hp runs rough at low speeds

[dan and margie]

My Dad has a 1975 Mercury 20 hp outboard, model number 200, serial number 4291718.<br /><br />It always used to run rough at lower speeds even though it ran ok at high speeds. Recently it started to idle real rough at slow speeds and then die.<br /><br />What he's already tried:<br />1. Cleaned carburator. <br />2. Put in a new float and needle.<br />3. Set the float level (but he's not sure if he got the float level right).<br />4. Put in new spark plugs.<br /><br />Thanks for any suggestions. He's in the middle of spring salmon season and wants to get back out on the Columbia River.

 

[NathanY]

Re: 1975 Mercury 20 hp runs rough at low speeds

Even though it idles real rough and dies, does it still run good at higher speeds? If so, I would check the fuel mixture and adjust as necessary. If not, I would check both cylinders for fire.