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Old 17 June 2008, 05:19   #1
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Adding 50hp carbs to Yamaha 40hp

I've been contemplating this for some time. My engine is a mint (Model 40V 6H4) 1995 Yamaha 40hp, 2-stroke, 3 cylinder Autolube. Spent a stress-free life on the back of a tender (originally registered to Princess Motor Yachts), then boxed up for 3-4 years before I stumbled upon it.

It powers my Zodiac 7-man Pro, and with 2 adults and 50 litres of fuel it clocks 34mph, but I'd like a bit more oomph, especially if I'm loaded with additional people.

I know the 40/50hp is effectively the same engine block, with the addition of the larger air-intake carbs and a larger exhaust manifold. What would happen if I was to simply to bolt on a set of 50 carbs. Would the idle adjustment and CDi ignition need to be altered in any way? I'm not thinking about adding the exhaust manifold - as this means around 2-3 hours work and getting access under the main block.
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Old 17 June 2008, 05:22   #2
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You have a PM
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Old 19 June 2008, 00:04   #3
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I've got a similar engine and have considered doing something like this as well. From what I understand, upgrading to the 50 hp exhaust manifold is very important for performance gains to be realized.

Nos4r2,

I'm also curious about what you can tell about this.
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Old 19 June 2008, 04:20   #4
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My understanding is that the manifold exhaust and carbs are the only difference, however I don't know what the implications are in terms of tuning?

Engine block needs to be removed to gain access to exhaust manifold (someone told me a 2 hour job). Then you have the problem of sourcing the correct parts. Some 50hp carbs come on to Ebay - but you'll need to source correct and compatible part. Exhaust manifolds are very difficult to find, and a whole engine may need to be purchased in order to break.

Might be worth getting quote from a Yamaha dealer - for the exhaust manifold and source second-hand carbs.
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Old 19 June 2008, 04:26   #5
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Quote:
Originally Posted by prairie tuber View Post

Nos4r2,

I'm also curious about what you can tell about this.
It's not something I can't tell, just that I have the yamaha parts lists here on PDF (therefore giving the definitive answer) and needed spartacus to contact me via MSNto transfer them,I didn't want to leave my email addy in plain view to be harvested by spammers.

PM me your MSN addy and I'll send you them so you can check the part numbers yourself against your motor and the 50hp Yamahas.
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Old 19 June 2008, 07:19   #6
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PM sent. Thanks
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Old 22 June 2008, 01:45   #7
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Yamaha 40Hp bits

If anybody does break one of these engines, I'm looking for a CDI unit at an affordable price for a 40Hp.... Help!
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Old 22 June 2008, 14:45   #8
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and I'm looking for a trim/ tilt unit for a 50 !
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Old 22 June 2008, 19:39   #9
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Quote:
and I'm looking for a trim/ tilt unit for a 50 !
There's one on Ebay just now - but doesn't look in great shape, plus they're asking 300 GBP to start.

See: http://cgi.ebay.co.uk/Yamaha-Outboar...d=p3286.c0.m14
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Old 22 June 2008, 20:39   #10
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He's asking silly money for everything there... Some of his 2nd hand stuff is more than it'd cost to import new pattern parts from the USA.
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