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Gas tank question

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Rusty rudder

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I have a 2- 6 gallon plastic fuel tanks that I use with a 1976 70 hp Johnson the problem I’m having is the engine will start up a idle but when I give it gas it dies now the vents are open and there happens with both tanks I even open the top of the tanks and still same problem......now I have noticed with the tops on tight and the vents open both fuel tanks will swell up over time when I open the tops pressure comes out ......guess I have bad vents put shouldn’t engine run with the tops off?
 
Nope, that's exactly what the tanks are supposed to do. The valves are one way, only allowing air into the tanks. They swell because the vent valve closes in the outward direction to prevent explosive fumes from building up around the tank.

Make sure your primer bulb is good and your fuel line is clear of any obstructions. If the tanks and line is good, then your problem is either related to fuel delivery in the engine, poor spark, or bad spark advance.
 
Ok so I’m closing the vents by turning the cap out when I think I’m opening the vents now even with the caps completely off the tank should the engine run ok?
 
Rusty rudder said:
Ok so I’m closing the vents by turning the cap out when I think I’m opening the vents now even with the caps completely off the tank should the engine run ok?
Click to expand...

If the engine wont run from either tank with the cap off then maybe a faulty fuel pump or air ingress into the fuel line ( unlikely to be both fuel lines if each tank has is own but worn O ring in connectors are a possible place for air to enter.)

Can you keep the engine running if you keep pumping the primer bulb? ...... Doing that will overcome air leaks at the connector and a faulty fuel pump
 
Ok I was using the same fuel line between the tanks and the motor,now I’m going to get a new line new connectors,new primer Bulb, this morning I opened the tanks so release the pressure tighten the tops until they clicked,then turned the vent caps down, if I’m under standing this correctly they should be open,checked tanks this afternoon and both tanks were swollen again, they swell up if the vent caps are turned in or out,now I’m thinking I needs 2- new caps with new vents maybe the fuel line is sucking in air due to the engine not running with the caps off and maybe the vents in the caps are not working correctly.what do y’all think and thanks for the information.
 
Plastic tanks and vents are problematic, especially when out in the hot sun. I collect and suggest the use of steel tanks for all my customers, but not everyone is in love with them. Plastic and UV don't mix well, especially when all that expansion and contraction is considered. If a plastic tank is used it should be kept in the shade if possible. Vent open when running vent closed when stored. Keep them in the shade.
 
Vents are normally open when turned out "counter clockwise"... and closed when turned in "clockwise". Has any manufacturer changed that? The fuel caps should stay snugged closed.

From what I understand, in either case, any tank, any fuel hose, fuel cap on or off.... the engine will run all day at an idle or a slightly high idle rpm... BUT... when throttle is applied to get up[ on plane, the engine dies out.

As "Timguy" suggests in not so many words, if the above holds true, that problem is caused by:

1 - A air/fuel leak somewhere between the fuel pump and the fuel supply. (fuel pump draws air)

2 - Clogged/fouled/gummed carburetors. (restricted fuel delivery)

2 - Sticking timer_base under the flywheel. (running with retarded spark)

In my experiences, it has about 98% of the time been related to carburetors fouled due to sitting.
 
Newer tanks don't have a release vent. As stated in post #2 above, the tanks are designed to expand with pressure. I disconnect my fuel line from the tank when not in use because I was worried that the pressure might blow my fuel pump diaphragm. I have two of those tanks running to a 90 hp evinrude. Check the rest of the fuel delivery system. Especially the high speed jets in your carbs.
 
Riopga.... Those new tanks you mention... do they have two small stainless steel pins sticking out of the housing where the fuel connector plugs onto?
 
Joe, If they do I haven't noticed them. Here is a write up about them. It has convinced me to add vents to mine!:

Our members are telling us that the new tanks aren't all they are cracked up to be," said Mike Vatalaro, executive editor of BoatUS Magazine.
Without a vent, typically a small screw-type fixture on the tank's cap or top, a portable gas container can swell up in the hot sun, forcing fuel into the outboard engine where it can spew inside the cowling and dribble into places it shouldn't be.
"Where the traditional tanks simply vent to the atmosphere, the new tanks won't vent until the internal pressure reaches 5 pounds per square inch. In the meantime, fuel could be forced up the fuel line into the outboard engine, many of which have no means to hold it back," Vatalaro said.
It's a fire hazard, in addition to polluting the environment, said Charles Fort, BoatUS director of consumer affairs.
"If this happened in an enclosed space...it could be catastrophic," Fort said, although he wasn't aware of fires resulting from the problem.
Many boaters have seen swelling of their new portable fuel tanks, which they hadn't experienced with older fuel containers, according to the National Marine Manufacturers Association, a Chicago-based trade group.
The new tanks, introduced in 2012 as the result of an Environmental Protection Agency rule change, were tested to remain sealed and safe even when swelling is visible. But if the pressurized fuel sprays out through the engine, or from a fuel line when it's connected or disconnected, it creates a dangerous situation.
Addressing the problem, Fond du Lac-based Mercury Marine Inc. partnered with Attwood Corp., in Lowell, Mich., to develop a fuel-line valve that prevents gas from reaching an outboard engine when the fuel isn't needed.
Mercury also developed a fuel-tank cap that, under a certain pressure, will vent gas fumes to lower the pressure to a safe level. But it won't allow fuel to leak out of the tank when it's jostled on a boat trailer.
Now, all of Mercury's outboard engines that use portable fuel tanks come with the technology that's EPA approved.
"Any time that you have fuel venting, there's always a safety issue...you just don't want to have gasoline spilling into your boat, or back by the engine," said John Neville, Mercury's director of global service parts division.
The issue has surfaced this year as many people have portable gas tanks without the fuel-demand valve. BoatUS recommends installing the $25 valve on tanks that need it.
"Without a vent, there's no way to release the pressure that builds up in the tank when it gets heated by the sun. The result — entirely predictable to boaters, but apparently unseen by regulators — is gas pouring out of the outboard and into the water, driveway or backyard. And before you ask, leaving the tank disconnected just results in the same gush of gas once you do hook it up," Vatalaro said on the BoatUS website.
The EPA says the change to the newer-style portable fuel containers has helped reduce harmful air pollutants.
"Nonroad engines contribute significantly to air pollution. In the Clean Air Act, Congress requires us to set emission standards that address the problem," the agency says on its website.
You could open the fuel cap and relieve the pressure, but that defeats what the EPA was trying to accomplish with its zero-emissions plan, and it's not always practical, said Charles Plueddeman, a freelance marine industry writer from Oshkosh.
If you don't want to install one of the valves yourself, go to a marine dealer and get a fuel tank that already has it, Plueddeman said.
 
I was already disconnecting my fuel line, but that expansion just sounds unnecessarily dangerous. I saw on another forum that there are little gas tank vents that you can buy to retrofit your tanks.
 
Just imagine the Johnson/Evinrude engineers of the 1940's, using a "closed system" to feed fuel to a motor without the use of a fuel pump. Total simplicity, automatically venting out the carburetor/crankcase/exhaust. This is way to ridiculous for today's world......isn't it?
 
Thanks for all the information I replaced both connectors,primer bulb,and fuel line toke boat the the river it started ok got up on plane and ran good all day I did have the top off fuel tank, I have now made vents and installed them on the highest part if the tank so I can now open them when I want to and close them when I want to the only thing I see wrong is there has never been any kind of fuel filters in fuel line so I’m going to install Inline fuel filters and we should be set.........I’m hoping lol!!!
 
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