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Old 02 September 2016, 03:46   #11
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Shane you might get lucky but supremesoundz hasn't posted on her for 2.5yrs.
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Old 02 September 2016, 08:26   #12
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Thanks for spotting this - do you or anyone else have any knowledge on the matter then.
Please advise thanks, Shane
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Old 02 September 2016, 08:54   #13
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I understand not everyone is always in front of thier PC so so if anyone else can help with the above it would be really appreciated,

Many thanks Shane
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Old 03 September 2016, 01:56   #14
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Quote:
Originally Posted by Shane Hethering View Post
Hi supremesoundz

Thanks for the post.
I also have a 20hp Yamaha 2 stroke outboard. Runs ok but I could do with more hp. The serial no 6A-9S-016773 it is mid to late 80's and I am trying to get more hp . It is the single carburettor model and I have put a 25hp carburetor main jet in which is slightly bigger from #135 to #140 , I also advanced the timing but no real difference, How easy is it to remove the washer from the the exhaust do I need to take the engine head off
I had a fairly recent discussion with a local, but very helpful and knowledgable outboard mechanic (one with real experience doing this sort of stuff rather than just servicing engines). My engine is twin carb and more modern but I suspect the same applies:

1. The carb body needs replaced not just the jets.
2. The exhaust manifold needs replaced (it may be possible to widen it out, but they are two different parts not just one part with a washer fitted loose in it. After many years of use in a hot salty environment, I am not sure I'd expect to attack it with a drill and not damage it.)
3. The timing needs adjusted.
4. Its a "relatively easy job" assuming everything unbolts easily. If any bolts shear then its just become a major effort. On a 30 yr old engine that is a very real risk for you.

Off the top of my head the parts (at Yam prices) were c. 600 GBP [can't remember if there was VAT on top]. Labour would be more on top, and for a motor of my age wasn't going to be worth it. For a motor of your age it definitely won't, unless you can find secondhand parts and DIY the work.

These engines hold their value well, but there is not much difference is price between 20 and 25, and you'll get no extra resale on a converted 20-25 (unless you happened to have a test rig to prove it was giving 25!)
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Old 03 September 2016, 08:35   #15
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>>>not much difference is price between 20 and 25, and you'll get no extra resale on a converted 20-25 (unless you happened to have a test rig to prove it was giving 25!)

Yes my thought was sell yours and buy one that's a proper 25hp. If you are careful with both buy and sell it will cost nothing.

Further I'd personally downvalue a DIY uprated engine because you have no idea if it was done to spec and how well.
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Old 05 September 2016, 04:20   #16
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Hi Poly,

Thanks for your very helpful post.
Yes my model is slightly different to yours, in that the Yamaha 1984-1986 20hp and 25hp outboard engine model shares the same single carburetor, which the local Yamaha dealer confirmed when I bought the 25hp Carb jet a few months ago. The only difference is the Exhaust tube and the Timing.

I went out yesterday and I adjusted the manual trim/tilt pin yesterday to lift up the bow more and it made a big difference on the boat speed, I was very surprised.

Poly, I am just wondering
1) What pitch propeller you are using? on your 20hp
2) Have you been able to find any alternative reed valves for the engine like the Boyseen Reeds, I know that they give much better performance from when I installed some on another engine (a 9.9 Yamaha) .. if so do you have a part number.

Many thanks Poly and look forward to your reply
Shane
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Old 05 September 2016, 06:52   #17
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Shane, I've not tried any fancy reeds. I can certainly make a couple of knots difference getting the trim right, and i recon I've lost a knot or more just with all the crap I carry (2 anchors, lots of rope, fire extinguisher, spare oil, spare fuel etc).

I've got a selection of props (all standard yam issue) in slightly different sizes. I can't remember exactly what they are and I've never been bothered to test them all on the same day in the same conditions. If i remember I swap between the biggest and smallest for running alone and with the whole family - but I mostly use the middle size and forget about it.
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