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Mariner Yamaha 28 hp won't run right

crankshaft

Contributing Member
I have this old Mariner Yamaha that is totally like new. IT came with 1 coil missing and another was hard to find. Got one that was for a higher Hp engine that the guy said would work and it does. At first I had the plug wires crossed and it tried to start but did not. Got the figured out and the engine starts but seems to have what I have seen called a "lean sneeze" IT runs but coughs and sneezes smoke then runs correct for a minute then does the sneeze again. I think this is usually the screw on the motor for proper mix. The screw with the spring does not seem tight. Anyone know the correct amount of turns out from bottom of the screw screwed in all the way? Anyway, it seem to run the same no matter how many turns it is out from bottom. I cleaned the carb that did not seem dirty and I thought it would run right, but the same sneeze and cough are there. Thought to clean the carb again but it seems clean.
 
Always add the year/model/serial# when asking questions.
You do a compression test?

You start at 1 1/2 turns out from lightly seated.
If you have a sneeze/cough or backfire??? then the motor might be sucking air someplace???
Starting fluid test: start motor, spray SF around the intake side of the motor, under the bottom carb and carb bases.
If that makes it run any different??? then it's sucking air someplace.
 
Yes, it has high compression 120
Always add the year/model/serial# when asking questions.
You do a compression test?

You start at 1 1/2 turns out from lightly seated.
If you have a sneeze/cough or backfire??? then the motor might be sucking air someplace???
Starting fluid test: start motor, spray SF around the intake side of the motor, under the bottom carb and carb bases.
If that makes it run any different??? then it's sucking air someplace.
High compression 120
 
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