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Old 10 July 2018, 10:12   #1
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mariner 40hp 2 stroke issue

After de-winterising the engine and finally getting it to start I let the engine warm up and idle for a while, once it was warm I raised the revs slightly as it was "coughing and spluttering" a bit but did not smooth out even at half throttle.
After a few more minutes it smoothed slightly but the revs permanently "hunt" at any throttle position causing the engine to judder more than normal, I have not had it on the water this year just asking what or where would be best to look at first to address the "hunting" issue ?.
Fresh fuel and clean plugs used.

thanks.
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Old 11 July 2018, 04:18   #2
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Check fuel filter and clean the carb (especially jets) would be my first port of call.
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Old 11 July 2018, 08:38   #3
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Do a pressure test then move on to carbs
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Old 12 July 2018, 16:00   #4
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Thanks for the replies, I had the engine pressure tested before winterising last year and was told it had good pressure on both cylinders.
As things are a bit financially tight this year I am going to have to solve this myself I have stripped and cleaned car carbs before but not outboard ones and looking at having to remove all of the oil injection gubbins looks a bit of a mare .
Is there an additive I could use first which could clean the carb through I appreciate it will not be as effective as stripping it but may help if so what additive should I use and also would it even work as there's oil mixing going on or is it injected after the carb?
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Old 18 July 2018, 03:02   #5
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If the carbs sound daunting, undo the hex bolts on the fuel bowls. This may indicate if there's contaminants present judging by what comes out. Fuel additives arent going to work, but if you want to try, then Forte products are pretty good.

Take off the air box to see that the choke butterfly isn't seized.
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Old 18 July 2018, 05:10   #6
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Thank you for your reply, I have done as you suggested and found the choke sticking, cleaned up and now working ok, I then drained as much fuel as possible and replaced now running as smooth as before thank you.
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