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Old 22 June 2016, 11:35   #11
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I wouldn't have thought it was worth the chew and expense if your smaller outboards running well .after all your only going to gain a couple of knots.id stick with what you have. as an example my 5.6 osprey with 130 Yamaha only does 38 knots. and the hull is rated at a max of 42
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Old 22 June 2016, 12:10   #12
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It was a friend who bought it off the sea scouts last year all the jets in the carbs were gummed up so he decided instead of re jetting the engine he would put a brand new set of carbs on converting it from the 75 to the 90 by just winding up the timing mark to the next notch. My 70 is a 1989 model and the 90 is a 2004 model he saying 1500 and I can swop them over just don't want to do it if there's not a significant increase in power I would like to be close to the 45-50mph mark at WOT.
Or he could have just cleaned the jets ????

If you're getting 42mph with a 70hp I'd think 50mph with a 90hp is a bit optimistic.
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Old 22 June 2016, 12:19   #13
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No I've seen the carbs brand new in the boxes there still sat there now 920 he has just payed for them hence the reason why he is saying 1500 for the swop which I think is fair. I have been up to ullswater with the rib and was getting 40mph but in the sea with the tide etc etc I seem to get roughly 35mph but just after some more speed really 😃
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Old 22 June 2016, 12:21   #14
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Just looked back over the post it was a typing error my engine is 99 model commissioned in 2001
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Old 23 June 2016, 07:56   #15
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I would go for it, if you know the 90 is in good condition. There was a 90 head on ebay a while back, not sure if it's still there, was for use on a 75 to 90 comversion. Easy enough to swap, the exhaust takes a wee bit more time, need to remove the powerhead to get to it.

I believe the yam 70hp is 849cc
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Old 23 June 2016, 12:04   #16
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I would go for it, if you know the 90 is in good condition. There was a 90 head on ebay a while back, not sure if it's still there, was for use on a 75 to 90 comversion. Easy enough to swap, the exhaust takes a wee bit more time, need to remove the powerhead to get to it.

I believe the yam 70hp is 849cc
but it isn't a 90 its a 75 with a set of new carbs and advanced timing he would still need to buy a head and do the exhaust or he wont be any further forward its starting to sound an expensive 3-4 knots improvement
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