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Old 21 February 2018, 12:56   #31
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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!
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Old 21 February 2018, 13:05   #32
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You need to rethink value for money when it comes to marine stuff unfortunately.
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Old 21 February 2018, 13:29   #33
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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!
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Old 21 February 2018, 13:30   #34
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Quote:
Originally Posted by duggie12 View Post
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.
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Old 22 February 2018, 11:40   #35
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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!
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Old 03 March 2018, 01:27   #36
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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?
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Old 03 March 2018, 02:03   #37
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If the timing was out would the sneeze only happen at low revs matt, or would it happen all the time?
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Old 03 March 2018, 05:28   #38
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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
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Old 03 March 2018, 08:59   #39
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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 ?
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Old 13 March 2018, 21:48   #40
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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.
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