Merc 120 New Problem

[brunowren]

For more background here is the previous post <br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=24;t=011912 <br /><br />Well got all the tank cleaned out and took the boat out Sunday... Idle out from the no wake zone... Hit the throttle and Wheeeeee up went the bow ... Ran at about 4100 rpm... slowed down to go to the floating restrooms..and turned it off...<br /><br />Then all the rest of the day it would only go 3100 rpm and that took alittle bit to get there? <br /><br />Seem to have lost my hole shot....<br /><br />I didnt mind much the boat ran all day and didnt die on me <br /><br />Any ideas what to look for on the lost 1000 rpm's

 

[Mahoney]

Re: Merc 120 New Problem

There are almost as many reasons you lost the power as there are rpm's you lost. I had an issue with using too cool of plugs on my 5.0 V8 and would foul a plug now and then. Engine would sound fine, but I lost about 700-900, rpm.<br /><br />It is by far the easiest check and fix and is worth a shot, check the plugs one at a time, if you pull one out that looks a lot darker than the rest take note. Restart the engine and trace that plug back to the dist cap and pull the wire while it is running. If the engine doesnt stumble and lose rpm's when you pull it, that plug is bad.<br /><br />I hope that is it, cause it can be fixed for under $3.00, if that is it, I would look into buying a hotter set of plugs though, or it will keep happening now and again.

 

[Mahoney]

Re: Merc 120 New Problem

I should correct myself, if those steps in my above post dont cause the engine to stumble, it could be a bad wire or something in the dist cap, but much more unlikely if it was running fine the first go round of the day.<br /><br />you can rule out the later by switching the bad plug to a different cylinder and repeat the steps.

 

[brunowren]

Re: Merc 120 New Problem

Great thanks Mahoney I will give that a shot