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  #1 (permalink)  
Old 05-10-2011
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Join Date: May 2011
Posts: 3
Default Lean idle cough

G'day

I have a 2002 50hp 2 stroke yamaha that's recently developed a lean idle cough.

I'm not sure how this had eventuated, but it has. I've owned this outboard coming up to 2 years now.

I'm running a racor fuel/water separator filter under the cowl, before the factory filter.

I've had the carbs off, cleaned and reinstalled, synchronized and tuned as best as i can but the problem still persists.

Fresh fuel is used and only quicksilver oil used as a premix 50:1. At higher revs say 1500 rpm the engine is great.

The oil injection was removed previously to me buying the outboard. I'm also running new plugs.

Does anyone have any ideas why this problem had developed and how to fix it?

Dave
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Old 05-10-2011
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Join Date: Dec 1969
Posts: 97
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Have you checked or replaced your fuel pump ?
Maybe its worth changing its membranes just to be sure that your carbs are supplied with the right fuel quantity
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Old 05-10-2011
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Join Date: Dec 1969
Posts: 334
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Have you adjusted the idle mixture screw?
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Old 05-13-2011
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Join Date: May 2011
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G'day

Have had fuel pump apart, membranes look fine, albeit they haven't been replaced. Mixture screws are set, but quite rich.

I;m going to spray some ether spray around the intakes and see if i can pick up a leaking gasket somewhere. Not likely but a permissibility.

Would timing also cause this issue?

Dave
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Old 05-13-2011
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Join Date: Dec 1969
Posts: 4,551
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It is always best to check all you can first to make sure they are all in spec (compression,spark, and timing, even fuel pressure/vacuum)and then work on the things you can not test like the fuel/air mix(carbs).

Sounds like you need to do a better job on the carbs, maybe use an ultrasonic cleaner and make sure you follow the service manual for setting the link and sync every time the carbs are reinstalled .
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Old 05-15-2011
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Join Date: Jan 2011
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I had the same problem on my 115 yamaha 2 stroke (1997),do a search for lean sneeze.I was trying to find my post but not sure how.At the time Rodbolt gave me some good advice on how to narrow down the problems.I do remember him saying do not keep runing it as it could cause piston damage.My problem turned out to be a bad fuel pump.Pretty easy to check the pump.If I remember right most of the other most likely causes were carb related.
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Old 05-15-2011
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Join Date: Jan 2011
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I just saw you had youre fuel pump apart.You need to check it with a vacuum gauge to verify its working right.I dont think I could find anything wrong with my diaghram either vissually but it was failing.
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  #8 (permalink)  
Old 05-15-2011
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Join Date: Jan 2011
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Try lean sneeze here.Maybe this was the forum I had posted my ? on.
Search Results - iboats Boating Forums
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  #9 (permalink)  
Old 05-17-2011
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Join Date: May 2011
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G'day

Thanks for all the replies guys. Engine has just been down to the mechanic who also had the carbs off, he also could find nothing wrong with them. He seems to think maybe the top crankcase seal is a bit worn, sucking in air intermittently. Is this a possibility?

He's re tuned it, I've just been for a run in it for about half an hour with 10 mins of idling, done a good job albeit the cough is still there when I run it on muffs at home. It only coughed once. it's much better than it was, but the underlying problem is still there.

Dave
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