Gas tank problem

[Roger Sr]

when i hook a gas line to this tank and run my motor.it forms a vacuum in the tank why? it's a metal tank. Roger

 

[wildmaninal]

Re: Gas tank problem

Is it a 2 line pressure tank or a more modern 1 line tank with a pump up bulb? If it is a modern style gas tank are you opening the vent screw on top of the fill cap?

 

[Roger Sr]

Re: Gas tank problem

it is a modern tank but has no vent screw. Roger

 

[jbjennings]

Re: Gas tank problem

It has a fuel pump that sucks gas out of the tank, that's a good thing. Your tank is not letting air in to replace the gas that got sucked out, so you're getting a vaccuum. It's got to have some kind of vent to let air in.
JBJ

 

[Roger Sr]

Re: Gas tank problem

it has a fuel gage. there may be a vent in that gage area? i'll look in the morning. thanks Roger

 

[wildmaninal]

Re: Gas tank problem

As Jbjennings said "It's got to have some kind of vent to let air in." Has the cap been replaced? Usaully there is a vent knob on top of the gas cap that screw in to close or screw out to let it vent.

Check it out let us know what you find out.

 

[jbjennings]

Re: Gas tank problem

Roger,
Just loosen the cap and see if that fixes your problem and the motor runs as expected. If so, you KNOW you have a venting prob. What kind of motor is it and what year/hp? Just curious,
JBJ.

 

[Roger Sr]

Re: Gas tank problem

I did open the cap yesterday that is how i ran it.the motor is a 93 15hp Johnson. in a post last week it had no spark at the plugs. i fixed that. the ground wire on the power pack was corroded

 

[F_R]

Re: Gas tank problem

Most OMC tanks have a vent built into the housing where you plug the gas line onto it. Attaching the gas line pushes in a couple of pins. One pin turns on the gas so it can flow and the other one opens the vent. In addition to that, the vent is a one-way valve so it can suck air in but not slop gas back out. It takes a (very) small amount of vacuum to pull the one way valve open. NO vent on the cap.

All this assumes you have a real OMC tank, not a Wal-Mart.

 

[Roger Sr]

Re: Gas tank problem

that is the kind of tank i have. the vent valve must not be working. here is a picture of my tank.

 

[F_R]

Re: Gas tank problem

That's what I figured. Frankly, I've never seen a vent that wouldn't open, but I suppose all things are possible. Looking at your picture, see the raised circular area where it says empty? If you were to remove the housing from the tank and look at the bottom side of it, there is a retainer washer in that circular area. Above that, there is a spring and a valve disc. That is the one-way vent. As I said, some vacuum is necessary to pull the valve disc down against the spring pressure. Maybe your valve disc has glued itself to the housing?? Maybe ethanol is deteriating them and we don't know it yet?? I dunno.

If you go to http://shop.evinrude.com/ and click on electronic parts catalog, then follow the prompts till you get to your motor and fuel tank, you can see an exploded parts list.

 

[Roger Sr]

Re: Gas tank problem

i Drilled a 1/16 inch hole in the cap. it works fine. going to take it out tomorrow an see how it runs. this is a project boat i just put it togather. wish me luck. it's my frist boat.

 

[jbjennings]

Re: Gas tank problem

Roger,
That's a nice-looking rig. I don't think you'll need much luck with it, those 15 johnson's are really good and reliable. Very smooth running and easy to start. Excellent choice! BTW, you can pick up a brand new plastic tank at walmart for 20 bucks and they work fairly decently.
JBJ

 

[wildmaninal]

Re: Gas tank problem

Just don't leave that tank out in the weather sense you drilled that hole in that cap. As long as it works though that's what counts.

 

[Roger Sr]

Re: Gas tank problem

I found an old vent valve screw that is just a little over an 1/8 inch. I'm going to drill and tap the cap for it. that should work. i really appreciate all the help. and input. all of you have helped me a lot.when i got this motor it has not been ran in nine years. and i had a time getting it running. but i did it.with some help from you guys and some others. the boat also set outside for nine years. so it looked real bad. it sure looks diffrent now.

 

[wildmaninal]

Re: Gas tank problem

I meant to say earlier that is a nice boat.

Try that vent screw on there and go have some fun on the lake .

 

[Roger Sr]

Re: Gas tank problem

Took it out on the lake today.every thing worked fine. had a grate time. thanks all! Roger.