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I have an issue with my 1998 25hp NMO Autolube Yamaha. It…

Hi I have an issue...
Hi I have an issue with my 1998 25hp NMO Autolube Yamaha. It has a backfire/sneeze on tick over only, it is fine through the rest of the power range. I have taken the carbs off had them fully cleaned and replaced all parts. I thought this was a pilot screw adjustment issue, but no matter what I do with the pilot screws it has no effect.
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Answered in 5 hours by:
1/13/2018
Charles
Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 4,908
Experience: US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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One thing that I have seen on the Yamaha carb is that the tip of the mixture needle cab become broken off inside the carb. Remove the needle fuly and inspect the tip to ensure that yours is not broken. Let me know what you see on it.

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Customer reply replied 7 months ago
I will check and let you know Charles, I will take a look in the morning UK time and get back to you

Thanks. I will reply when I log on and see it.

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Customer reply replied 7 months ago
Hi Charles, I checked the mixture screws, they were fine. While I had the carbs off again, I decided to check the slow running jets, to my surprise there was some dirt in one of them (I had just had them ultrasonic cleaned).When I put them back together, the engine seems to be running fine, but I have not taken it out for a run as yet. Once I have done this I will let you know.

Thanks for the update. If the pieces that were in the carbs were white in color, look to replace the inline fuel filter, as it may be parts of it that is clogging the idle tube.

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Customer reply replied 7 months ago
Checked the fuel filter no issues there, I am thinking it was just some residual dirt in the system. Once I give it a run I will let you know if all is well.

That makes sense. Please keep me informed.

Charles
Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 4,908
Experience: US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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