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Old 10 September 2019, 14:14   #1
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40hp Yamaha 60hp carb's

Hi,

I bought a 1991 Yamaha 40 hp autolube. I want to convert it to 50 hp or more. I know I need the exhaust and the carb's.
I also know 70hp carbs can be used. I am offered a set of 60 hp carb's. Would that give more power than 50 hp carb's?
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Old 10 September 2019, 15:14   #2
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I looked at this very scenario over 10 years ago and Yamaha 50hp parts were as rare as rocking horse poo, so now it's like looking for the Holy Grail. Can't answer regards 70hp, etc.
Adding 50hp carbs to Yamaha 40hp

My understanding is that model 40V and 50G shared the same block, so work on that premise. Even if you have the parts you need to remove the engine block to access the exhaust manifold. On a 1991 engine (28 years old) you run the very real risk of sheared bolts, drilling them out, and retapping. Best you're aware as it's not for the faint hearted.
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Old 10 September 2019, 16:23   #3
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Originally Posted by spartacus View Post
I looked at this very scenario over 10 years ago and Yamaha 50hp parts were as rare as rocking horse poo, so now it's like looking for the Holy Grail. Can't answer regards 70hp, etc.
Adding 50hp carbs to Yamaha 40hp

My understanding is that model 40V and 50G shared the same block, so work on that premise. Even if you have the parts you need to remove the engine block to access the exhaust manifold. On a 1991 engine (28 years old) you run the very real risk of sheared bolts, drilling them out, and retapping. Best you're aware as it's not for the faint hearted.
Donít work on that premise as the 40V and 50G are completely different.

The 40V is based on the small block 50hp (ie 1991 50D) but with a much improved leg / lower shock mounts.
The 50G is the downtuned 60/70hp fitted with the 55hp gearbox.
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Old 10 September 2019, 17:12   #4
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Donít work on that premise as the 40V and 50G are completely different.

The 40V is based on the small block 50hp (ie 1991 50D) but with a much improved leg / lower shock mounts.
The 50G is the downtuned 60/70hp fitted with the 55hp gearbox.
Isnt it the 50H thats the same block as the 40v?
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Old 10 September 2019, 17:18   #5
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Isnt it the 50H thats the same block as the 40v?
Yip.

Best plan if wanting to use all factory parts is find a 50g which is the 850cc block and fit 70b carbs. Sure rolfhat will be on soon with advice.
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Old 11 September 2019, 02:07   #6
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70hp carbs will fit the 40/50, I think you'll actually be better with the 60hp carbs. I put 70hp Yamaha carbs on a 50 Tohatsu, lost a wee bit of mid range and gained a very small amount of top end. Not really worth it in my opinion unless you have a highly modified engine, you might be ok with 60hp carbs but I would go for 50hp ones
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Old 11 September 2019, 09:40   #7
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Originally Posted by fishman009 View Post
Hi,

I bought a 1991 Yamaha 40 hp autolube. I want to convert it to 50 hp or more. I know I need the exhaust and the carb's.
I also know 70hp carbs can be used. I am offered a set of 60 hp carb's. Would that give more power than 50 hp carb's?

reeds will be different too -
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Old 11 September 2019, 10:12   #8
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reeds will be different too -
No, the 40 and 50 hp (3 cyl) engines are the same, except for the exhaust tuner and carb's.

Reeds for 30/40/50 hp are the same.
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Old 12 September 2019, 06:37   #9
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Go for carbon reeds if you want performance, don't want the steel ones breaking and going into the cylinders
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Old 13 September 2019, 03:06   #10
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Go for carbon reeds if you want performance, don't want the steel ones breaking and going into the cylinders
I just ordered reeds from CCMS.
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