itsonlymoney
regular
Reged: 21/06/2003
Posts: 4501
Loc: UK
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So were do I find a parts diagram for a mercury 2.5/3.3. One assumes its the same script for my 2.5 ie. change a jet ????
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BillyBloater
regular
Reged: 09/01/2006
Posts: 356
Loc: UK
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Quote:
So were do I find a parts diagram for a mercury 2.5/3.3. One assumes its the same script for my 2.5 ie. change a jet ????
try here
http://www.usboatsupply.com/outboardparts.php
Cheers
Billy
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"He is not only dull himself, he is the cause of dullness in others."
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misterg
regular
Reged: 31/10/2003
Posts: 1544
Loc: N. Wales
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Quote:
Quote:
2.5 & 3.3 Mariners are the same engine, but the 2.5 is restricted by the throttle slide not opening fully - it is physically to long to do so. (I suspect this applies to Mercuries, etc. too.)
So how would one get round this and make the slide open fully ?
One could presumably buy a replacement throttle slide for a 3.3, or if one is impecunious, one can carefully cut about 6mm off the top of ones existing throttle slide (look into the throat, and hold the slide so it is flush with the top of the venturi and mark where it needs to be cut). One then needs to bend the throttle linkage to give full travel of the modified slide. One's done it, and it works, but is of limited benefit on a heavy rubber dink (more noise, but not really any faster - I've since acquired a mercury 3.3 and it's just the same).
N.B. this engine has a carb with a slide, so both petrol and air are controlled by slide opening (petrol via the needle valve attached to the air slide). Looks like the engine in the original question has a butterfly valve for the throttle, so not the same.
Not wishing to get into an argument, but I don't think the jets are the whole answer, because these could only give you more fuel, not more air, and you need both. I still suspect there is a restriction elsewhere (either on the throttle opening, or somewhere in the air intake, or exhaust system). Maybe the alternative jets are for high altitude use, or something ?
Andy
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BillyBloater
regular
Reged: 09/01/2006
Posts: 356
Loc: UK
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Quote:
The HP restriction is VERY unlikely to be done by restricting the airflow (throttle). I repeat, it is done by the carb jet sizing. So just change the jets. Parts 2, 3, 4. Quite cheap, less than a £fiver per item. Note, each one of these 3 parts is listed twice, with a different dimension code. One set will be for the 9.9, t'other for the 15hp. Which kinda proves my point
I agree that the jets apear to be different but if I increase the jet size only, the engine would run rich wouldn't it.
i.e the same volume of air but more fuel !
How do they get the mixture back to being right?
Billy
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"He is not only dull himself, he is the cause of dullness in others."
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itsonlymoney
regular
Reged: 21/06/2003
Posts: 4501
Loc: UK
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So not worth the hassle then ?
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Nick_H
regular
Reged: 20/04/2004
Posts: 3002
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I bought a Suzuki 4 hp 4 stroke, and to turn that into a 5hp you just flip over the little moulding that the throttle cable attaches to, done. I don't think that's the case with yours though.
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Davy_S
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Reged: 31/01/2003
Posts: 792
Loc: Greece (Ionian)
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On the smaller engines it is pretty easy, increase jets, take out the restricter. I think you have worked out for yourself you need to increase RPM to increase power, ie, push more air through, In the bigger engines the CD ignition modules need to be changed to increase rpm, its a bit like changing the engine management system, it aint cheap! good luck.
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jfm
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Reged: 16/05/2001
Posts: 7818
Loc: London/Antibes
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Good point. Can you examine the carb a bit more. Maybe there is a restricter ring inserted to the air intake tube, that you can remove? I very much doubt it will be a case of making the butterfly open more fully, much more likely to be a restricter ring. There are lots of US outboard tinkering forums - have you googled them?
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misterg
regular
Reged: 31/10/2003
Posts: 1544
Loc: N. Wales
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So not worth the hassle then ?
Not unless you're bored  - I'm sure my old rigid f/glass dinghy would have gone a bit faster, but a dead-loss on the flubber. F-N gearbox on the 3.3 is much more use than the extra HP.
Andy
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BillyBloater
regular
Reged: 09/01/2006
Posts: 356
Loc: UK
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I didn't see any sign of restriction either side of the carb. googling the US sites is a great idea, I will report back when, or if, I find the answer !!
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"He is not only dull himself, he is the cause of dullness in others."
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