Lean sneeze problem

[duggie12]

No beamish that's beyond me I'm a bit out of my depth as it is

I didn't poke any wires through but I have an air compressor machine so used that + lots of carb cleaner

I've actually got it going much better. It now sneezes much less and only really does it when you turn the throttle really quickly. If turn it at a normal speed it doesn't seem to be sneezing. I didn't replace that gasket with the kink but I did put a bit of silicone round it - I thought that might seal it if there was any leaks ?

Thanks v much to all, especially yourself fenlander for your help

[duggie12]

By the way came across this on another forum similar to this one it's called f ribs and sibs. Appears to be a bit of an issue:


*Just a bit of a heads up for anyone that buys/owns a Suzuki DF9.9 - DF15.*
There appears to be somewhat of an issue when slowly going up through the revs. As the carb swaps from idle to main jet, you get a very slight engine hiccup/pop back through the carb.*
I had my outboard in at*Pennine Marine*(Skipton) for some other issues, the mechanic (John) went completely through the motor trying to eliminate this problem,**Suzuki technical got involved too, but no fault was found. It appears to be somewhat of an inherent issue.**
It certainly does not impair the running/performance of the motor, and i would say, unless you're mechanically minded, you probably won't even notice its there.**
I’m a massive fan of Suzuki motors, In general, the build quality, weight reduction and reliability is second to none, it certainly hasn’t put me off buying or recommending their super light, quiet and highly fuel efficient engines.
I know a few folk with these outboards, all appear to have the same issue, although as stated, very minimal. The Suzuki DF9.9 / 15hp are very popular outboards, Most folk seem to keep them, once purchased. I looked for about 6 months before I found a tidy, well looked after one. They seem to be as rare as hens teeth.

[duggie12]

P.s. fenlander I think the engine does have one of those accelerator pumps, it's on the other side of the carb so you can't see it when the carb is on the engine. There doesn't seem to be any way of adjusting it though, the set up is a bit different to the one in the manual you sent me

[Fenlander]

>>>If you're is flashing back through the carb have you checked the valve clearances & timing etc?

Yes like Beamishken that would be my next area of investigation if simple checks don't bring sufficient improvement. Compared to a 2-stroke designs which have porting that make a flash back in the carb quite possible with a lean mixture the 4-strokes don't suffer so readily. It would usually be that the spark is somehow firing at the wrong time when the inlet valve is open... or the inlet valve is sticking open or it's seat is eroded losing pressure.

Re the fribs and sibs guy's experience I'll accept what he says but I always wonder if a dealer might be giving a plausible response to pacify an owner when they can't get to the bottom of an issue. I've seen that so many times over the years in the car industry.

Re the accelerator pump have a look in the carb throat as you snap the throttle open... you should see a spray of fuel if it's working.

[duggie12]

My timing belt is long overdue a change so if I keep the engine until the end of this year I'll get it done at the next service

Yeah I know what you mean fenlander if something wasn't happening when it was new and it now is, surely that's a fault rather than an inherent problem

Look in the carb throat - I'd have to take it back off, is that what you mean?

I know carbs aren't the most complicated things in the world, but when I was cleaning it today it did make me wonder how people came up with the idea and invented it. Amazing things !

[Fenlander]

Can you see into the carb to see the throttle butterfly... or can you do so if you take off a bit of inlet tract leading to the carb? If you can see the butterfly you should see the acc' pump spray.

[duggie12]

Ah got you. I'll give it a try and see what I see.
But am I in theory compromising the gaskets every time i remove the carb?
Cheers

[Xk59D]

Suzuki parts are literally pennies, just replace the gasket.

[duggie12]

I was £18 quid a set,must be buying them from the wrong place!

[Xk59D]

18 quid for a set of gaskets is cheap for an outboard.

Last week I paid 35 quid for only a yamaha impeller, not a kit, for an 8hp, My Suzuki 200 was 38 quid for a full impeller kit a few weeks ago.

[duggie12]

Ah right got you, when you said literally pennies I though you meant just that and that I'd been ripped off. Although they do seem steep for a few bits of thin rubber. If it solves the problem it will be well worth it thou!

[Xk59D]

You need to rethink value for money when it comes to marine stuff unfortunately.

[jwalker]

Since this happened after you serviced the carb, have you checked the carb float setting to ensure the fuel level in the carb is correct?

I'm going to give you the sequence of events inside the carb from the point the throttle is opened because if you are familiar with it you can determine which area might be giving you a problem.

When opening the throttle slowly: air and fuel as an emulsion is drawn into the carb barrel and on into the engine, down stream and at the throttle butterfly through the idle screw orifice and then the progression hole(s). While this is happening (as the throttle is opening ) depression is pulling on the main nozzle and lifting fuel which has passed thought the main jet. (This fuel may or may not be mixed with air from the air corrector jet. The mixing takes place in the chamber after the main jet. This chamber is known as the emulsion tube but some simple carbs don't have this level of complexity.) This fuel is not yet issuing from the nozzle. Further opening of the throttle will result in the fuel being lifted high enough to issue from the nozzle, at this point fuel will stop issuing from the idle system. This is the critical point because if the fuel is late at the nozzle there will be a mixture weakness, if it is early there will be a mixture richness. Since the fuel is being lifted from the float chamber level, the fuel level in the chamber determines that critical point - too low = weak, too high = rich.

Now, if you open the throttle quickly all this goes on in an instant BUT... because the fuel is heavier than air it has greater inertia and takes much longer than the air to respond to the throttle opening so there is momentarily air with no fuel, this is where the carb fuel pump comes in. It injects a wodge of fuel directly into the air stream the moment the throttle is opened to attempt to fill in that hole in the carburation.

For completeness, there is another reason that a week hole exists when the throttle is snapped open and it is to do with the sudden drop in pressure within the inlet tract and the effect this has an any airbourne fuel. You can ignore this for the purpose of your fault finding.

So, presuming you have no air leaks, no errors in the piping, and the carb is assembled correctly, the things which can upset the progression are: blockages within the slow run system so it finishes fueling too early, wrong float level so you have a rich or week change over from the idle system to the main system or a faulty carb fuel pump so you have a hole in the fueling until the main jet can catch up with supplying fuel. It's unlikely to have too much fuel from the carb fuel pump but it is possible.

Good luck with it!

[beamishken]

Originally Posted by duggie12

Ah right got you, when you said literally pennies I though you meant just that and that I'd been ripped off. Although they do seem steep for a few bits of thin rubber. If it solves the problem it will be well worth it thou!

If you've got to strip the carb a few times using the old gaskets won't hurt maybe a thin smear of silicone if required. All gaskets are technically 1 shot but the carb gaskets aren't particularly critical in comparison to say a head gasket.
I wouldn't be fitting new gaskets every time until I knew it was sorted.

[duggie12]

Cheers for the explanation j

No I've not checked float level. I just put it back together as it was. I'll look into that at the weekend thou

Beam that's good i don't need to replace them every time i strip the carb, good to know that thanks!

[matt h]

Float lever has to be right, It has been mentioned before by FL but to me the poss the timing out slightly. I think your description is popping back through manifold, would you agree?

[duggie12]

If the timing was out would the sneeze only happen at low revs matt, or would it happen all the time?

[beamishken]

It maybe the timing is fixed via a crankshaft position sensor which may not be adjustable but as you advance the throttle the timing will advance too (which is part of the cause of the lean sneeze because of the lack of fuel the revs haven't picked up but the timing has advanced)
I'd be carefully checking the accelerator pump to be sure it is squirting a fine jet of fuel as you snap the throttle open

[matt h]

It could well be fixed. Thoroughly check out the obvious easy things like carb first then latterly timing. Water in fuel can make it “sneeze” ish also.

Just a thought. Inlet valve closing fully?
Broken inlet valve spring?
Compression test ?

[Lee1]

Did you poke anything metal through the jet holes? Of so the jets may have been corroded and your poking may have changed the jet hole size, I've made this mistake a few times on cleaning old jets so now I just fit new ones if they look blocked.