Lean sneeze problem

[duggie12]

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?
Thanks

[Fenlander]

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?

[Fenlander]

Oh yes... does your carb have an accelerator pump... if so are you sure this is delivering a squirt of fuel?

[duggie12]

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

[duggie12]

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.

[duggie12]

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.

[duggie12]

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!

[Fenlander]

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.

[duggie12]

Thanks fenlander
I'll let you know if I ever get to the bottom of this!

[Fenlander]

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.

[duggie12]

Yeah I've still got that manual it's really handy. I'll investigate that tomorrow.

Do you know the weird thing?when on the boat the engine hardly sneezes, but in the bin it does it all the time. I know that sounds ridiculous but it's true !

One other thing fenlander if you don't mind - do you have a view on the instant gasket stuff you can buy? I was going to get some rather than ordering new ones is it's a bit of a pain.
Thanks

[Fenlander]

>>>do you have a view on the instant gasket stuff you can buy?

In an emergency just acceptable but otherwise I'm an OE fibre/rubber gasket guy. Others may think differently.

[duggie12]

Fenlander been watching lots of you tube videos - a lot refer to air and fuel idle mixture screws - I've just been adjusting one. Do you think there could be another screw somewhere? I'm going to have a look tomorrow as not at home just now, but I thought you might know. Thanks

[Fenlander]

There are usually two screws for idle settings... idle speed screw and idle mixture screw which controls the air/fuel ratio.

The idle speed screw and its setting is described in section 2:13 of the pdf manual. I seem to remember yours had a capped idle mixture screw and with my advice you removed the cap so you could adjust it. I can't remember if you have a small tach... if not you should to set the idle speed if nothing else.

Like this... https://www.ebay.co.uk/itm/112809858...84.m1436.l2649

The idle mixture screw is the one you revealed under the cap last year and I'll just paste in a reminder of the procedure I gave remembering this needs to be in a water tub in forward gear...

First screw it in counting turns until it bottoms out gently. Make a note of this and return it to the existing position. Then in a bin of water get it warmed up idling in forward gear. If it isn't keen bring up the idle speed with the linkage screw just enough for it to continue idling OK.

Then turn in the idle mixture screw until it just starts to hesitate and note how many turns that is from fully screwed in. Then turn out the idle mixture screw until it starts to hesitate and find out how many turns out from fully in that is.

Set it to a position half way between the two which should be the ideal... sometimes they pick up from idle best just a fraction screwed out from the halfway point.

If during this mixture setting it improves the running enough to make the idle too high back the speed screw off to a normal idle and go through the procedure again.

[A1an]

I've never seen a 'lean sneeze' in a four stroke before.

[Fenlander]

>>>I've never seen a 'lean sneeze' in a four stroke before.

Possible misunderstanding of terms.... or me not being precise with that term. I assume Duggie is suffering a hesitation, cough, burp or sneeze depending how you would describe it but not the firing through the carb you can get with a 2-stroke.

So I'm advising on the basis he's suffering whatever you like to call the noise/effect with any engine that briefly finds itself without enough fuel delivery as the throttle is opened.. nearly dies then jerks away as it just fires rather than stalling.

[beamishken]

I had a similar problem with a 25 yam 4 stroke
I had to put the completely stripped carb in a ultrasonic bath several times before I cured the problem.
I'm pretty sure it was down to dried up fuel leaving deposits in the tiny jets and holes in the carb
You can buy ultrasonic baths pretty cheap on eBay and they come in handy for all sorts of things

[duggie12]

I'm not sure of the terminology either but basically makes a bang and there is a flash at the air intake. Not sure if that's a misfire or a back fire or a lean sneeze

At it just now fenlander but still no joy. Cheers for sending that post, I actually dug that out yesterday to remind myself what you had said

I don't appear to have a one of those accelerator pumps

By the way do outboards have air filters?if mine has one I don't see it !

Thanks beam I'll maybe look into that if today's messing about doesn't help. I've stripped the carb (again) and blowing compressed air through everything (again)

[beamishken]

Originally Posted by duggie12

I'm not sure of the terminology either but basically makes a bang and there is a flash at the air intake. Not sure if that's a misfire or a back fire or a lean sneeze

At it just now fenlander but still no joy. Cheers for sending that post, I actually dug that out yesterday to remind myself what you had said

I don't appear to have a one of those accelerator pumps

By the way do outboards have air filters?if mine has one I don't see it !

Thanks beam I'll maybe look into that if today's messing about doesn't help. I've stripped the carb (again) and blowing compressed air through everything (again)

No air filter as such as it's not working in a dusty environment you should have some form of plastic baffle on the front of the carb though.
I stripped and blew thru the 25 carb several times with air and carb cleaner and still couldn't get it to work correctly that's why I bought the ultrasonic bath. It still took several goes in the bath to get it all cleaned up and working correctly
If you're is flashing back through the carb have you checked the valve clearances & timing etc?
They can give similar symptoms but most likely culprit is carb making it run lean as you open it up

[paintman]

Originally Posted by duggie12

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

That damaged 'O'-ring/gasket needs replacing if only to rule it out as a problem.
Did you try & clean any jets or passageways with bits of wire or other objects?