Proper fuel line diameter for my 80hp?

BonairII

BonairII

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I'm currently using 1/4" ID fuel line for my '67 Johnson 80hp motor. I went to buy a fuel tank connector for the portable tank I bought and noticed that all the connectors seem to 3/8ths or larger, so I started to wonder if my fuel line is too narrow.

I checked my service manual and can't seem to find any info on the stock fuel line size.

I'm starting to think my fuel line should be at least 5/16ths ID.
 
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boobie

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Re: Proper fuel line diameter for my 80hp?

Minimum 5/16 ". 3/8 " the best. In this case, bigger is better.
 
BonairII

BonairII

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Re: Proper fuel line diameter for my 80hp?

Is it safe to assume that I should change the hoses on the motor also? Could the 1/4" hose have caused any performance issues?
 
F

F_R

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Re: Proper fuel line diameter for my 80hp?

No, that is not necessary. Your 1967 motor was made before OMC even thought about bigger hoses, which came about when the V-6 motors weren't able to get enough fuel. Your stock hoses are perfectly fine, and no performace increase will happen by usng larger ones. Having said that, if buying a new tank hose assembly, there is no reason not to just get the larger one, even though not necessary.

BTW, the small tank hose was used on motors up to at least 140hp V-4s, so not to worry about your little 80hp.
 
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Chriswalden

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Re: Proper fuel line diameter for my 80hp?

The fuel line inside the engine cowling from the fuel line quick disconnect to the fuel pump should be a larger diameter line, but the line from the fuel pump to the carbs is going to be of a smaller diameter because the fuel flow needed to the fuel pump requires a high VOLUME and the fuel flow from there to the carbs requires PRESSURE to keep the bowls filled. No need for a large diameter line there.
 
BonairII

BonairII

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Re: Proper fuel line diameter for my 80hp?

Chriswalden said:
The fuel line inside the engine cowling from the fuel line quick disconnect to the fuel pump should be a larger diameter line, but the line from the fuel pump to the carbs is going to be of a smaller diameter because the fuel flow needed to the fuel pump requires a high VOLUME and the fuel flow from there to the carbs requires PRESSURE to keep the bowls filled. No need for a large diameter line there.
Click to expand...

I'm not seeing the sense of having larger diameter line to the fuel pump, only to decrease diameter AFTER the fuel pump. I guess I'll stick with the 1/4" ID(just replaced a few months ago) that I already have installed on the the entire system...unless someone can show me where my motor would benefit from 5/16ths or larger.
 
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Will Bark

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Re: Proper fuel line diameter for my 80hp?

In this case just go with what F-R said. You'll be ok.
 
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