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Old 09 November 2015, 18:13   #1
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Yamaha 90 rebuild

Just finished this project I started 12 months ago, Had four of these 90's I'd collected so built one good one, with some tweaks. Rebored to +0.50mm, far too many hours spent flowing and porting the block, lightened and balanced rods, balanced pistons, skimmed head, carbs venturi machined out on lathe, ditched the choke butterfly's and fitted a Merc primer, two stage boyesen reeds. Removed leg silencer can and made my own exhaust tuner to a proven design, and turned a set of solid engine mounts. Resprayed it and 2k clear coated and new decals from US.

Need to sort the hull for it now

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Old 09 November 2015, 18:21   #2
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Nice! What's it going on?
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Old 10 November 2015, 04:31   #3
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Niiice!!!
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Old 10 November 2015, 05:17   #4
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Looks mint! What LWP is that? Thinking about one for my 70ces.
I think I'm right in saying you can put the gearbox from a 55/60hp 2 cyl on them, much smaller. A guy in america went from 74 to 80mph with that change.

Any photos of your new exhaust?
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Old 10 November 2015, 08:53   #5
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It's a bobs lwp but it didn't really fit very well to the 90 box so I cut it down a bit and tig'd up the side outlet and drilled and tapped it for a top exit.

Yes the 55 box bolts straight up to the 90 but you have to cut and shut the drive shafts as the splines are different. I did think about doing it on this but restricts the prop choice. The 55 and 90 share the same leg casting and shock mounts which probably explains why the lower mount castings don't last very long if you are "pushing on"

The exhaust tuner is an exact copy of the well known aftermarket US one, I had a similar one years ago from RaceMarine and it worked well.
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Old 10 November 2015, 09:19   #6
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Old 10 November 2015, 13:41   #7
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Quote:
Originally Posted by phantom 19 View Post
Just finished this project I started 12 months ago, Had four of these 90's I'd collected so built one good one, with some tweaks. Rebored to +0.50mm, far too many hours spent flowing and porting the block, lightened and balanced rods, balanced pistons, skimmed head, carbs venturi machined out on lathe, ditched the choke butterfly's and fitted a Merc primer, two stage boyesen reeds. Removed leg silencer can and made my own exhaust tuner to a proven design, and turned a set of solid engine mounts. Resprayed it and 2k clear coated and new decals from US.

Need to sort the hull for it now

Cool, we like it!! Do you have a motorcycle background? 'Flowing and Porting' that brings back some Ace memories!!
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Old 10 November 2015, 15:48   #8
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Nice job. Love seeing a 2-stroke brought back to life looking as sweet as it rolled off the production line in Japan.
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Old 17 November 2015, 06:35   #9
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Why are there no piccies of the rebuild
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Old 17 November 2015, 07:34   #10
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A thing of Beauty, well done for saving it. It would look great on just about anything
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