New fuel tank problems

[swordfish455]

Hi Guys,
My fuel in the new 70ltr underfloor tank seem's to evaporate leaving just 2 stroke oil behind.Someone mentioned that the breather could be too big ?
Any Advise as I don't know if I should start modifying it.
Thanks Sam

[Blackened]

G'day

That sounds pretty damn strange and I cannot see how that much fuel could evaporate alone.


What size are all your breather and filler lines?

Is someone stealing your fuel?

What brand id your tank?

How old is the suspect fuel?

Dave

[FNQCairns]

What Blackened said X2.

any more info??

cheers fnq

[PADDLES]

hi salvatore. do you have an oil injected motor? is there oil in your fuel line and fuel filter? i used to have an old black max merc and the oil would wick it's way down the fuel line from the injection pump (must have had dodgy seals) and even get into the fuel filter if i left it for any period of time. i simply used to disconnect the line from the motor and squirt a litre or two out of the fuel line into a jerry can before i used it if i had left the boat unused for a bit. used to get an awesome james bond style smoke screen on a cold morning at the ramp before i figured this out.

[garman1]

Oh Paddles, nearly spilt coffee everywhere with the james bond bit :D, visualized this boat disappearing in the smoke and when it cleared the boat had gone.............now I know how to get a head start on everyone else getting to the best spots, smoke out the boat ramp, lol..... classic!!!!!

Also i have a good excuse to keep my 2 banger,(to get a fishing advantage) and not upgrade to a 4 banger or an etec....... oh james you've done it again..;D..lol

Again Paddles, good one ;D;D;D

cheers Garry

[swordfish455]

Hi Guy's,

Thanks so much for the help.
Fuel line is standard fuel line.
However breather is 3/4 inch.
It only completely evaporates when I have a small amount of fuel left and the remainder of the tank is full of air.
Tank is custom made alumiuim with the pick up coming from underneath.
Fuel is new and it only happens when it sits there for 4-8 weeks and all I end up with is oil in the tank 100-200ml.
I put into the tank a 50:1 fuel and oil mix.
So why do I end up with straight oil ?
If anyone can work that one out your a legend.
Regards Salvatore

[FNQCairns]

So at 50:1 that would amount to 5 or 10L left in the tank that evaporates, not impossible I suspect. If your tank is flat bottomed you will have a large fuel surface area to volume so as the tank gets down evaporation is GREATLY increase in comparison to a V shaped tank.

It is highly likely if yours is flat bottomed that evaporation is the cause, cure is to keep it full it will react to increased changes in temperature slower as a benefit.

cheers fnq

[PADDLES]

that is a fairly big breather salvatore, i've got a 170L flat bottomed tank in current boat with two breathers at 3/4 inch each. i've got a 4s motor so obviously don't notice the oil, but i do notice a fuel smell if the boat (and therefore fuel) moves around and even if i'm walking past i can sometimes smell it. so it isn't totally improbable that it's evaporating. is it possible for you to put some sort of a valve in the breather hose to limit it's area whilst the boat is parked?

you're right garry, that smoke screen saved me from those damn ruskis a number of times

[swordfish455]

Hi Paddles,

I think your on the mark with the valve somewhere in the breather line.This should slow air travel and only open when pressure builds up.Unfortuntely the tank holds 70litres of fuel and the motor is only a 25hp johnson.I have never filled it over half as the fuel may go off.Yes I know its way to big.Live and learn as they say.So if I don't get any better suggestion I will go with yours.
Cheers Salvatore

[Moonlighter]

Hey Paddles

Same problem used to happen to a friend's 225 Evinrude on his Haines.

Redland City Council cancelled their mosquito spraying contract for Cleveland point after seeing him smoking up the whole region every time he started up the the old 'Rude when it had been sitting a while! (Made it hard to follow the bugger out to his favourite spots though - damn smoke-screen)!

Grant

[PADDLES]

you still want a little air to come back in so you don't create too much of a vacuum but still restrict the free flow of air and vapour.

g'day grant, you're right, we do know how to breed a pretty mean mozzy up here at beachmere but a good puff of 2 smoke sorts em all out. the new suzuki just doesn't have the same "mystique" about it that the old black max used to.