what fuel line diameter?

[Big Daddy Braddy]

91 pro v 200. Replacing hose and bulb, found 5/16 before bulb and 3/8 after bulb to the engine.

[Sequoiha]

That engine does not need 3/8 fuel line, 5/16 is fine from the tank to the engine. make sure the line below the deck is labeled as so,

[BQUICK]

Can't hurt to go with 3/8. Most outboard fuel systems are marginal to begin with with their diaphragm fuel pumps.

[boscoe99]

Yamaha hose for a V6 motor is usually 8mm. Rounds closest to 5/16ths" ID.

As with batteries and wire sizes, it does not hurt to err on the upper end of the size needed. Just as a margin of safety.

[tmann45]

Check your calculator...
8mm = 0.3150, 5/16" = 0.3125"
3/8" = 9.5mm
on my calculator.

[rodbolt17]

6mm/ roughly 1/4"
8mm roughly 5/16ths
10mm roughly 3/8ths
11mm roughly 7/16ths.
13mm roughly 1/2".

I can count better than I spell .

[Sequoiha]

Can't hurt to go with 3/8. Most outboard fuel systems are marginal to begin with with their diaphragm fuel pumps.

It can hurt to go with 3/8, that is exactly right, and with the bigger fuel line there is more fuel to pull thru the fuel line equals more weight and more suction which can lead to issues with marginal fuel pumps..

[tmann45]

It can hurt to go with 3/8, that is exactly right, and with the bigger fuel line there is more fuel to pull thru the fuel line equals more weight and more suction which can lead to issues with marginal fuel pumps..

You are correct that the larger fuel line will have more fuel and therefore weigh more, but it is not the weight the pump is fighting, it is the pressure, and the pressure is the same whether it is 5/16" or 3" hose.

It almost never hurts to use larger fuel hose, it will reduce the pressure drop due to friction and that will reduce the load on the pump.

[rodbolt17]

cant hurt but the ONLY motors,so far, that Yamaha requires rigging with 3/8th hose are the V8s.

[Sequoiha]

You are correct that the larger fuel line will have more fuel and therefore weigh more, but it is not the weight the pump is fighting, it is the pressure, and the pressure is the same whether it is 5/16" or 3" hose.

It almost never hurts to use larger fuel hose, it will reduce the pressure drop due to friction and that will reduce the load on the pump.

where did that come from,, Pressure, what pressure, Oh you mean negative pressure, or inches of mercury,, or Vacuum which is a made up word in the english language,, and the marginal negative pressure fuel pumps they were talking about the bigger fuel line does matter because more fuel weighs more which creates more negative pressure, or (vacuum) which will cause a running issue..
In any case we are talking about the suction side of the pumps not the pressure side.. wake up..

[tmann45]

where did that come from,, Pressure, what pressure, Oh you mean negative pressure, or inches of mercury,, or Vacuum which is a made up word in the english language,, and the marginal negative pressure fuel pumps they were talking about the bigger fuel line does matter because more fuel weighs more which creates more negative pressure, or (vacuum) which will cause a running issue..
In any case we are talking about the suction side of the pumps not the pressure side.. wake up..

Sorry, I don't need to be awake to discuss fluid mechanics, been doing it for 30+ years.

Now let me get back to my nap.

[rodbolt17]

freak fracking idiot anganeers again.
for the past 30 plus years or so I have seen MOST hulls rigged with 3/8th fuel line up to either the fuel water separator or primer.
never made a sheet of diff.
this sheet aint rocket science or I would be to stupid to do it.
example.
1992
OMC says ANY motor above 120 HP MUST be rigged with 3/8ths line.
Yamaha shipped there motors in that year with 8mm lines.
Suzuki in that same year shipped the 225 EFI motor with 6 MM lines.
all worked.
fix the issue forget the line size.
and actually in 1992 I worked for all 3 above.