Is fuel line too long?

[Earl D]

Following the lead from a very informative series of videos on YouTube, I am converting my 12' V-hull into a bass boat. The conversion will have a rear deck, cockpit just forward of the rear deck and then a forward deck. With the modifications I am making, a fuel tank of any size will not fit behind the remaining what use to be the rear bench seat.

I have a nice, new, 6 gallon fuel tank. The tank will comfortably fit just forward of the what use to be the forward bench seat. The distance from the tank to the motor on the transom will be about 8'.

I wouldn't think there would be any problem whatsoever with fuel traveling through a hose from the tank to the motor over that distance. But, I, believe it or not, have been wrong before. Is there any reason to not put the fuel tank that far away from the motor?

Thanks for any comments.

 

[Earl D]

Following the lead from a very informative series of videos on YouTube, I am converting my 12' V-hull into a bass boat. The conversion will have a rear deck, cockpit just forward of the rear deck and then a forward deck. With the modifications I am making, a fuel tank of any size will not fit behind the remaining what use to be the rear bench seat.

I have a nice, new, 6 gallon fuel tank. The tank will comfortably fit just forward of the what use to be the forward bench seat. The distance from the tank to the motor on the transom will be about 8'.

I wouldn't think there would be any problem whatsoever with fuel traveling through a hose from the tank to the motor over that distance. But, I, believe it or not, have been wrong before. Is there any reason to not put the fuel tank that far away from the motor?

Thanks for any comments.

I posted before finding other posts on this subject. I would delete this but can't find a way to do that.

 

[LDUBS]

Did you find out you were OK with the long fuel line?

 

[Earl D]

I posted before finding other posts on this subject. I would delete this but can't find a way to do that.

Yes, thanks

 

[Tinny Fleet]

Sounds like the OP is now squared away, but for others with the same problem who use this site to research this issue in the future I offer one additional tip learned long ago.

If your boat has a smallish older outboard, say under 15 hp or so, these outboards originally came with a 1/4" ID fuel line. My experience with this issue has been mostly with the OMC's in the 4 1/2-15hp sizes (although I've had other larger motors as well).

Fast forward to today, most OEM and aftermarket fuel lines are 5/16" or 3/8" diameter. No big deal if the line is short (like 5-6 feet long as they come out of the box/blister pack). Intuitively the nice new thick lines seem like they would be easier to pull fuel through than the older thinner ones. Not so, as I learned.

It is a bigger deal if that line has to stretch a lot further, given that the little powerhead mounted mechanical fuel pump has to pull all that volume through for a much longer distance. To compound things the new - longer - line may be 8-10' if measured in a straight line from the motor to the tank, but the reality is you need several feet more of hose to tidily have the hose go from the center of the boat where the tank might be sitting to the gunnels, then run down the length, then back to the center to plug into the motor.

I tried using a nice thick line at first but it caused fuel starvation issues.

These went away when I returned to the 1/4" ID OEM sized hose.

Hope this helps.

 

[blufrog1]

This has me wondering if it could be a solution for lack of high speed response on my 87 johnson 15hp. Certainly worth considering.

 

[sonny1]

Six gallon tank and live well going in forward part of 14 foot Lonestar.

 

[LaqueRatt]

That makes perfect sense that a larger fuel line might tax the pump. That little bump in diameter I suspect leads to a great deal more "weight" in fuel inside the line that needs to be moved. Good to know and noted for future reference.

 

[thill]

When I have a very long fuel line, even in a 25 HP jon boat, I make the main line 3/8" to prevent flow restrictions. But that's just me.

 

[thill]

Let me explain that. It's not just "what I do" but there is a reason.

When I have a very long fuel line, even with a 25 HP motor, I make the main line 3/8" to prevent flow restrictions. The thinner and longer the straw, the more effort it takes to suck X amount of fuel through it per minute. Try to drink through one of those tiny coffee straws and you will see this in action.

The weight of the fuel in the line doesn't matter much in distance, but it DOES matter when you increase the lift height. The weight difference between a 1/4" line and a 3/8" line is very little if only lifting a foot or two. At a 6' lift height, it becomes a slightly larger issue. At 50 foot, it's a big difference. Obviously, this is not much of an issue in a tin boat.

In most tin boats, when you move the fuel tank forward, often the tank ends up higher, and gravity actually helps push fuel through the line. If high enough, it can even pressurize the fuel line. That is why they put an anti-siphon valve @ built in fuel tanks, to prevent a damaged fuel line from siphoning fuel and filling up the hull and causing a very dangerous situation.

This is a good reason to clean or replace a sticky anti-siphon valve rather than removing it.

The same lift theory applies to tank size, too. If the bottom of the tank is 2 feet below the engine, it doesn't matter if it's one gallon or one thousand gallons, the pump only has to lift it 2 feet. The trick is having a tank big enough for your longest trip, but not so big that the fuel goes sour before you use it up.