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Old 10 October 2016, 13:11   #11
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Some years ago I made an OMC 20 into a 25.
I had to remove the restrictor between the carb and the manifold, and install a larger main jet. That's all. More air/fuel, but in balance.
I cross referenced parts lists to be sure.
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Old 10 October 2016, 13:47   #12
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Quote:
Originally Posted by kaman View Post
Howdy.
A few questions if i may......
How old is your engine Bigplums?
Whereabouts in the country are you?
Lastly who informed you that you couldn't upgrade it to 20hp?
Age is July 2007

I am in Suffolk near Ipswich

It was Barrus UK who informed me based on the Seriel number
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Old 10 October 2016, 14:54   #13
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Had a quick look in the garage
The part number for the 15hp carb as far as I can see is
3BHF A5 016
The 20hp according to the box it came in is
3BH-03100-0
If your engine is the same model / stable mate of my Tohatsu and it has the same 15hp carb I don't see why the upgrade wouldn't be possible.
Hope this helps.
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Old 11 October 2016, 01:18   #14
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Quote:
Originally Posted by kaman View Post
Had a quick look in the garage
The part number for the 15hp carb as far as I can see is
3BHF A5 016
The 20hp according to the box it came in is
3BH-03100-0
If your engine is the same model / stable mate of my Tohatsu and it has the same 15hp carb I don't see why the upgrade wouldn't be possible.
Hope this helps.
Thanks for the help but I think my engine was the block which was made for the 9.9, 13.5 and 15 hp and is less cc than the current model which is a 15/20 hp. Mine I am told has less cc than the current model.

It actually goes quite well with the little valiant 3.4 so I will be happy with what I have which is very unlike me

Dennis
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Old 11 October 2016, 03:57   #15
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I think the advice BP has been given may well be correct. Currently as Kaman has found both 15hp & 20hp are 351cc and basically the same.

Back around 2006/7 the 15hp was a 323cc... there was no 20hp but they jumped straight up to a 526cc 25hp.... hence no simple carb upgrade 15hp to 20hp.
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Old 11 October 2016, 04:10   #16
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Yup that will be right enough then if it's the older version of the 15hp. Oh well no harm trying.
Next time around I'll be going straight for the highest HP that I can get for the given model of engine rather than changing carbs etc later on to up the HP.
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Old 12 October 2016, 03:02   #17
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I am a little diaspointed that I cant do the upgrade but it was going to cost over 350 and I was not sure if it would have given me much of an advantage. As I said I love the way the 3.4 handles as it is and I have much bigger boats if I want to go power mad

Dennis
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