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Old 09 October 2014, 05:35   #1
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2 stroke "sneezes" then cuts out

Morning all,

We've got a lovely little Yam 30hp, 3 cylinder 2 stroke on the back of the Searider.

It's a 2001 engine but dry stored and not installed or run until 2012. It's been running like a little gem until recently.

It had a couple of moments where it lost power and we've taken it to our local yamaha dealer who has stripped and cleaned the carbs and that problem seems to have been cured (although i've not given it a proper run yet to be sure of this)

However, the problem it has now is that after a run, when left idling for a few minutes (when tying up) it will do a little sneeze / chuff and then cuts out.
It doesn't have a tacho but the idle "sounds" a little high to my ear.

Any pointers?

I'm reluctant to take it back to the dealer as on two occasions they've basically told me that 2 strokes are crap and I should buy a new 4 stroke from them.
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Old 09 October 2014, 05:45   #2
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Assuming everything else is OK (plugs/leads/fuel filter/carb clean etc) this is commonly caused by an idle mixture screw set too lean. The 2004 Mariner 15 I bought last month was set up like this and I sorted it during a service.

It would start fine from cold but if left idling in the tank it would tend to slow and die sometimes with a "chuff". Also it could do the same chuff as you tried to open the throttle from idle and sometimes die/almost die before the revs picked up again.

I measured (by turns) where the idle screw was then set it up myself by the manual and the issue has gone. The screw is now about 1/4-1/3 turn richer than before.

Not sure about yours but mostly you should set the idle mixture with it in forward gear.
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Old 09 October 2014, 07:04   #3
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As a 'rule of thumb' start with the pilot air screw 1. 1/2 turns out.
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Old 09 October 2014, 08:29   #4
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Almost certainly a blockage in the idle jet of the bottom carb
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Old 09 October 2014, 08:51   #5
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Cheers All.

Looks like a consensus!
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Old 09 October 2014, 09:18   #6
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Yep as said in the above would be the first ports of call. however if that does cure it there is something else but let us know first
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Old 09 October 2014, 09:31   #7
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Quote:
Originally Posted by matt h View Post
Yep as said in the above would be the first ports of call. however if that does cure it there is something else but let us know first
Hi Matt,

I'll get them back to have a look at the idle screws.

What else might it be?

Cheers

Duncan
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Old 09 October 2014, 11:36   #8
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Wind all the mixture screws out to 3 whole turns
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Old 09 October 2014, 11:36   #9
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Carbs out of sync ie mixtures
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Old 09 October 2014, 13:29   #10
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Quote:
Originally Posted by Fenlander View Post
Assuming everything else is OK (plugs/leads/fuel filter/carb clean etc) this is commonly caused by an idle mixture screw set too lean.
I too would start by turning the mixture screws richer just a teeny tiny bit, and see how it runs.

Quote:
Originally Posted by Fenlander View Post
Not sure about yours but mostly you should set the idle mixture with it in forward gear.
I do both in gear and out of gear. Along with blipping the throttle and slow throttle increases, along with chopping the throttle and slowly letting it down. A listening ear can tell a lot about mixture.
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