New gas tanks

[RZR2007]

I bought a new gas tank for my boat 2 weeks ago ('89 johnson 90hp) I have no problems running on the first tank which is an old tank (both 6 gal portable), now within 10-15 min. of running on the new tank, the motor stumbles, comes back up, stumbles. The vent was unscrewed in the middle of the cap, so I put the old lid on the new tank and the problem disappeared. I thought the cap was bad, went to West Marine, gave me a new replacement, same problem. Went back, they called the manufacturer, seems the new guidlines require the fuel system to be pressurized to 5 PSI and the caps will not vent until this is reached. My motor will not run with the new system, they said Marine patrol has also started issueing tickets for new fuel tanks with the old caps on them, but it's ok to use the old cap if it is on the old tank. Has anyone else had an issue like this??

 

[nwcove]

Re: New gas tanks

lol....whats old is new! i just posted a question about an old 1950's pressurized fuel tank set up, which were discontinued for issues about having gas under pressure. im told it was quite dangerous.
is it negative pressure ie -5psi (vacuum in the tank) and the cap allows air in? or positive pressure...venting a burst of fumes out?
negative pressure sounds more reasonable, maybe you need a fuel pump kit?
your post really peaked my interest......hope to mhear from some more knowledgable memebers.(my thoughts are only thoughts....not based on fact!! lol)

 

[RZR2007]

Re: New gas tanks

lol....whats old is new! i just posted a question about an old 1950's pressurized fuel tank set up, which were discontinued for issues about having gas under pressure. im told it was quite dangerous.
is it negative pressure ie -5psi (vacuum in the tank) and the cap allows air in? or positive pressure...venting a burst of fumes out?
negative pressure sounds more reasonable, maybe you need a fuel pump kit?
your post really peaked my interest......hope to mhear from some more knowledgable memebers.(my thoughts are only thoughts....not based on fact!! lol)

I was thinking a weak fuel pump as well, but wouldn't it show itself at upper RPM levels on either tank? It will run all day long with out missing a beat as long as the old style cap is on. I couldn't talk the wife into holding the little vent button down the whole trip,lol! I can leave the new tank sitting for an hour with the vent open, as soon as I push it in, you can hear the pressure bleeding off, it says on the cap to push it in before removing the cap so gas doesn't blow all over you....

 

[ajgraz]

Re: New gas tanks

New cap + small drill bit = solution to problem?

 

[RZR2007]

Re: New gas tanks

New cap + small drill bit = solution to problem?

Absolutely! Just wondering if anyone else was having any issues with the new tanks, also something to keep in mind if problems should arise after purchasing a new tank....

 

[Chris1956]

Re: New gas tanks

Leave the cap a bit loose.

 

[nwcove]

Re: New gas tanks

this new cap thing has me confused???? if the fuel pump sucks fuel, through a single line, where does the pressure in the tank come from? if the cap says to bleed pressure off before opening it must be under positive pressure......not vacuum as would be suspect for a motor starving for fuel. so how does suction create pressure downstream of the pump? (if your motor still has its original fuel pump, a rebuild/replacement might be a good idea anyway! it just could be old and tired ..like me. lol)

 

[RZR2007]

Re: New gas tanks

this new cap thing has me confused???? if the fuel pump sucks fuel, through a single line, where does the pressure in the tank come from? if the cap says to bleed pressure off before opening it must be under positive pressure......not vacuum as would be suspect for a motor starving for fuel. so how does suction create pressure downstream of the pump? (if your motor still has its original fuel pump, a rebuild/replacement might be a good idea anyway! it just could be old and tired ..like me. lol)

Guess it is building pressure by sloshing around, ever leave one in the sun for very long? It'll swell up pretty quick! The fuel pump very well could be getting a little tired...
Chris1956, If I leave the cap a bit loose It'll spill a bit of gas out, I have just been putting the old cap on when I run the other tank out and swap to this one, when I do this, all is well again. I think nwcove is probably right about the fuel pump, it's been on there for a while....

 

[Fed]

Re: New gas tanks

If that 5 PSI venting is both positive & negative it will cause havoc with larger OMC motors, their vacuum switches trigger at 7" Hg which my little converter tells me is about 3.5 PSI.
I'd also like to know more about this.