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Old 19 February 2018, 07:26   #1
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Lean sneeze problem

Hello all (and hopefully fenlaner is reading this!)
I've had a lean sneeze problem with my suzuki 15hp 4 stroke since I cleaned my carb last year. The engine never had a lean sneeze before I cleaned it which makes me think it's something I've done when I rebuilt it.

The lean sneeze seemed to go away for a bit but it's now back !

I've cleaned the carb again and replaced the gaskets. I've tried new fuel. I've adjusted the idle mixture screw. Does anyone have any suggestions as to what else I can try to get rid of the lean sneeze?
The engine actually runs perfectly well, but I'm planning on selling it and the lean sneeze makes it sound terrible.
One thing I did notice was the gasket on the air intake (where it clamps up against the carb) seems to have a very small kink in it. Photo attached, you can see it if you look closely. This gasket wasn't replaced as it didn't come with the kit I bought. Could that be the culprit ? Possibly letting air in?
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Old 19 February 2018, 08:29   #2
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Country: UK - England
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Make: Aerotec 380
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I'd sort that gasket before looking anywhere else. Is it a Suzuki specific thing... square section with/without a lip... or an O-ring that you could buy by size?

Following on from that... and no disrespect intended... are you good at setting up the idle mixture? Are you doing it by turns... or by listening to the engine... and have you tried what you judge as the correct position then going 1/4 turn rich?

Lastly are there any vac pipes that you've disturbed near the carb?
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Old 19 February 2018, 08:38   #3
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Oh yes... does your carb have an accelerator pump... if so are you sure this is delivering a squirt of fuel?
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Old 19 February 2018, 09:25   #4
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Thanks for the reply fenlander
I think it's a suzuki specific thing as it has a lip
I've no real experience with setting the mixture. But I've spent ages trying every different position so feel if it was the mixture screw then I'd have sorted it via trial and error
There is an orange and black pipe in the vicinity, but I've left them well alone

I don't actually know what an accelerator pump is so don't know if I've got one but I'll do some research.

I feel the problem has to be related to when I stripped the carb. It was fine before I did that and wasn't immediately after
Thanks
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Old 19 February 2018, 09:27   #5
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Out of curiosity do you know what the black bung is that covers the idle jet? Seems odd. The main jet doesn't have one.
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Old 19 February 2018, 09:29   #6
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Oh one other thing in case it's relevant. The air intake was quite oily and so was the carb when I stripped it there.
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Old 19 February 2018, 09:31   #7
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I emailed my mechanic. He said to change the spark plugs but from the research I've done it's not a spark plug issue. I'm determined to get to the bottom of it!
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Old 19 February 2018, 09:49   #8
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In truth fitting new plugs was a reasonable first step call from a mechanic without the OB in front of him as it's an easy thing to do.... but if they are fairly new and/or in good nick then they probably won't do much. Having said that it is possible for spark plugs to break down under load even when they idle OK. I've just had to change the set on daughter's Honda Jazz due to a "burp" and hesitation as you pulled away but it idled and ran quickly OK.

The rubber bung is on the parts list and I know of more than one make that has that arrangement just on the idle jet. What happens is that the fuel goes into the main jet and then there's a passageway that feeds it to the idle jet. That plug needs to be a snug fit so it's sealing properly.
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Old 19 February 2018, 09:51   #9
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Thanks fenlander
I'll let you know if I ever get to the bottom of this!
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Old 19 February 2018, 10:14   #10
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Did you keep a note of the manual pdf I linked a while back...

https://www.maritimepropulsion.com/files/pdf/1001408

Section 4-11 explains the Acc' pump arrangement and section 4-9 how to check/set the pump lever gap.

The Acc' pump is to deliver an instant spray of fuel into the carb throat as you snap the throttle open to compensate for the sudden gulp of air as the throttle valve opens before the main jet fuel flow has had time to react.
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