EPA FUEL TANK WOES.

[JSGOLD]

We replaced our 8hp tiller motor with a newer Mariner 9.9 remote steer and I did a stupid thing by buying a new Attwood fuel tank that apparently has no ventilation cap. I installed a new mercury hose with the nipple on one end as I figured this was a better connection that I had on my Evinrude(it leaked sometimes when cold) and what I find is that this tank swells up, even with a small amount of fuel in it and fuel escapes around the nipple. I just came back from removing the battery and found a puddle of gas on the floor....And it has done so one other time while sitting in the garage while we had the 9.9 on a engine stand. I tightened the hose well, but ti still leaks it seems. Does not seem to matter if the cap is tight or not it still swells unless the cap is darn near off. let my vented tank go with my 8hp, any ideas? i dont think you are supposed to use sealant on those nipples, but may be wrong. I also noticed hesitation on the 9.9 when we used it the first time. I wrote it off as perhaps a dirty carb, as motor has not been used much except as a kicker. But the motor idles well, and when it gets going it runs great, no misfires, nothing. it runs slow and high speeds well after it gets warmed up. Perhaps still a carb issue but I wonder if the tank can be causing this as well.

 

[MH Hawker]

Their at least two things you can do, one is to order a old style fuel cap or add a vent to the existing one

 

[UncleWillie]

... I installed a new mercury hose with the nipple on one end as I figured this was a better connection that I had on my Evinrude(it leaked sometimes when cold) and what I find is that this tank swells up, even with a small amount of fuel in it and fuel escapes around the nipple. I just came back from removing the battery and found a puddle of gas on the floor....And it has done so one other time while sitting in the garage while we had the 9.9 on a engine stand. I tightened the hose well, but it still leaks it seems. Does not seem to matter if the cap is tight or not it still swells unless the cap is darn near off. let my vented tank go with my 8hp, any ideas?

If all your leaks are at the fitting you added, it should be obvious that the problem, is the fitting, not the tank.
The tank and cap are is designed to hold pressure to over 5 psi before they will vent.
The vent in the cap will allow air IN during operation, Opens on Vacuum, but not OUT unless overpressure.
Normal pressure in the tank will be in the 1-2 psi range.
The tank will balloon somewhat. This is completely normal and to be expected.

Putting a vent in the cap of the tank will just allow the fuel vapors to escape from the tank and settle into the boat.
If the fitting is leaking, fix the leak! Don't try to re-engineer the tank.
That is denial of the real problem.

 

[JSGOLD]

I have tightened the nipple as tight as I can and it still does not hold. Is there a sealant that can be used on the threads? I thought on those brass nipples they were to just be tight and that was it. But the tank really swells at times and it seeps out around the threads.

 

[UncleWillie]

Teflon Pipe Tape, or my favorite, Permatex Aviation Form-a-Gasket #3 come to mind.
Available at many Auto Parts Stores.

 

[smokeonthewater]

Don't use tape on a fuel system. There are a few sealants you can use but tape is a bad idea as bits of it can end up in the fuel supply.

 

[JSGOLD]

The aviation stuff is simply not found around here but I did recently buy some permatex that is gasoline rated. It dries to a pliable state and did well where I used it. It might work I guess. It was expensive stuff too. Will try it and report back.