Mercury sneeze

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catchin1

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Oct 27, 2013
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My 91' model 25 merc @ idol will miss every now and then. Ive noticed it before on other motors over the years. Mechanic says it referred to as "The Mercury Sneeze". An issue of air/fuel mixture says he. I understand that air temp and such effect fuel mixtures. My question is anyone one else heard it referred to as that and should I try and adjust? It runs fine on the top end.
 
The smaller merc 2strokes are a bit tempermental at idle in neutral. Once they are in gear and just a little gas is given they are a smooth as any 2stroke has ever been.
 
If it is a high pitched chirp you need to check for vacuum leaks or ritchen up your mixture. It can also be indicative of a cracked reed
 
A sneeze is indicative of lean running condition.. Did he suggest to richen it up a little bit to remedy it? 2 strokes do not like to run lean in any temp/condition..

I own/owned several Merc's and they do not normally sneeze when running properly..
 
Lean. Or timing too far retarded. Or both.

Either one is dependent on throttle position. It can be lean and retarded, but if the throttle is closed a little the sneeze may go away.

The sneezing goes away when the throttle is advanced usually because the linkage advances the timing at the same time, even though the throttle may not move.

All that assuming there are no air leaks and the rest of the ignition and fuel system are in good condition. Not just merc's either. Quite a few smaller Yamaha's do it too but it's easily tuned out once the cause is identified.
 
If your fuel line is old, or the bulb, check them, as I had the "sneeze" or "chirp" at idle, replaced both and no more sneeze or chirp. The old gas line was in bad bad shape I am shamed to say, my fault on that.
 
I just dealt with this on the 90 hp Merc on my Wahoo this past summer. After adjusting all the other stuff to spec (timing, idle adjustment, etc.) it came down to the book saying back out the idle air screws on each carb 1-1/4 turns. It wouldn't run right at that setting. I went to 1-1/2 on each carb and wow, it idled great after that. It think searching around revealed that most people recommend the 1-1/2 vs the 1-1/4 the manuals say. I would check those idle air screws to see where they are to start with.
 

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