venting gas tank.advise needed
Thread Starter
Burning Brakes
Joined: Sep 2008
Posts: 753
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venting gas tank.advise needed
1969 427
i was on the racetrack last sat and i was loosin a lot of gas from right side of tank during left hand turns. the track manager forced me to get out of the track after 5 laps
found the problem
-i use an electric fuel pump and no fuel return line ( i bought the car like this)
-Bubba left the return line from the tank unplugged : just a few inches hose there... spitting out gas when turning
-i have a vented 69 gas cap ( with key locking) with rubber gasket and a one way valve ( air allowed in but not out: there's a small hole with a ball )
is this the right solution? ( be aware , race track use , so lot of fuel slosh in the tank and my engine is damn thirsty in race conditions so fuel level goes down quickly)
- plug the return line hose
-remove gasket from gas cap so tank can breath in and out
-enlarge the tiny hole on gas cap to allow more air
am i wrong ?
i was on the racetrack last sat and i was loosin a lot of gas from right side of tank during left hand turns. the track manager forced me to get out of the track after 5 laps
found the problem
-i use an electric fuel pump and no fuel return line ( i bought the car like this)
-Bubba left the return line from the tank unplugged : just a few inches hose there... spitting out gas when turning
-i have a vented 69 gas cap ( with key locking) with rubber gasket and a one way valve ( air allowed in but not out: there's a small hole with a ball )
is this the right solution? ( be aware , race track use , so lot of fuel slosh in the tank and my engine is damn thirsty in race conditions so fuel level goes down quickly)
- plug the return line hose
-remove gasket from gas cap so tank can breath in and out
-enlarge the tiny hole on gas cap to allow more air
am i wrong ?
Last edited by elle88; Jul 5, 2011 at 02:09 AM.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
If you replace your cap with a vented one and plug the return at the tank you should be good.
Personally I would install a vented cap and then hook up the return line using a T at the carb and drill a .070 hole for the return like Lars does.
There are return regulators also if you want to be able to adjust the return flow.
On your existing keyed cap if all you need is air going in why not just leave it alone.
The usual directions for the keyed cap says to remove the gasket to make it a vented cap but with the racing you might have fuel sloshing out around the cap and draining down the sides of the tank,stinky and maybe dangerous with the fumes it might make.
Personally I would install a vented cap and then hook up the return line using a T at the carb and drill a .070 hole for the return like Lars does.
There are return regulators also if you want to be able to adjust the return flow.
On your existing keyed cap if all you need is air going in why not just leave it alone.
The usual directions for the keyed cap says to remove the gasket to make it a vented cap but with the racing you might have fuel sloshing out around the cap and draining down the sides of the tank,stinky and maybe dangerous with the fumes it might make.
Thread Starter
Burning Brakes
Joined: Sep 2008
Posts: 753
Likes: 0
Thanks Roger
i have to check better but i think that the return line has been removed on my car or cut short so not easily reusable...
yes fuel slosh at the gas cap could be a problem , even if i think that the slosh will not touch the gas cap area since it's in the middle of tank. btw my car has a rubber gasket around the gas cap and from there a rubber hose that takes the excess gas down under the car near the licence plate area
do you think that allow air in is enough (vented cap)?is there no need to vent the pressure out too?or just it doesn't matter?
i have to check better but i think that the return line has been removed on my car or cut short so not easily reusable...
yes fuel slosh at the gas cap could be a problem , even if i think that the slosh will not touch the gas cap area since it's in the middle of tank. btw my car has a rubber gasket around the gas cap and from there a rubber hose that takes the excess gas down under the car near the licence plate area
do you think that allow air in is enough (vented cap)?is there no need to vent the pressure out too?or just it doesn't matter?
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
I think if you are removing fuel at a high rate then you only need "air in".
If the car sits in the sun and the fuel expands you might need the "air out" but being aware of this you can always just loosen the cap until you get back on the race track.
Have you looked at the top of your tank,some tanks have a special valve built in for pressure. I'll see if I can find you a pic of the valve.
I do think that this type cap would do both.
http://willcoxcorvette.com/product_i...ducts_id=24545
If the car sits in the sun and the fuel expands you might need the "air out" but being aware of this you can always just loosen the cap until you get back on the race track.
Have you looked at the top of your tank,some tanks have a special valve built in for pressure. I'll see if I can find you a pic of the valve.
I do think that this type cap would do both.
http://willcoxcorvette.com/product_i...ducts_id=24545
Thread Starter
Burning Brakes
Joined: Sep 2008
Posts: 753
Likes: 0
Roger
i will try to see if i can reach with fingers that valve area and see if it's there.is it on the left or right?
your suggestion to open sometimes the gas cap to release pressure make sense.
here are some pics of my gas cap.
the hole is really small and when the ball is seated there's not that much air flow at the end . during racing, gas is drained from the tank quickly : let's say 1 gal every 3 miles. i believe that vent is not enough
look at the gas cap gasket and draining hose. the gasket seems nicely sealing around the filler neck.i may leave the gas cap without its inner gasket when at the racetrack and let the excess gas flow down under the rear of car, far from exhausts.
or just remove the ball from the gas cap and enlarge the outer hole...
i will try to see if i can reach with fingers that valve area and see if it's there.is it on the left or right?
your suggestion to open sometimes the gas cap to release pressure make sense.
here are some pics of my gas cap.
the hole is really small and when the ball is seated there's not that much air flow at the end . during racing, gas is drained from the tank quickly : let's say 1 gal every 3 miles. i believe that vent is not enough
look at the gas cap gasket and draining hose. the gasket seems nicely sealing around the filler neck.i may leave the gas cap without its inner gasket when at the racetrack and let the excess gas flow down under the rear of car, far from exhausts.
or just remove the ball from the gas cap and enlarge the outer hole...
Last edited by elle88; Jul 5, 2011 at 10:56 AM.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Roger
i will try to see if i can reach with fingers that valve area and see if it's there.is it on the left or right?
your suggestion to open sometimes the gas cap to release pressure make sense.
here are some pics of my gas cap.
the hole is really small and when the ball is seated there's not that much air flow at the end . during racing, gas is drained from the tank quickly : let's say 1 gal every 3 miles. i believe that vent is not enough
look at the gas cap gasket and draining hose. the gasket seems nicely sealing around the filler neck.i may leave the gas cap without its inner gasket when at the racetrack and let the excess gas flow down under the rear of car, far from exhausts.
or just remove the ball from the gas cap and enlarge the outer hole...
i will try to see if i can reach with fingers that valve area and see if it's there.is it on the left or right?
your suggestion to open sometimes the gas cap to release pressure make sense.
here are some pics of my gas cap.
the hole is really small and when the ball is seated there's not that much air flow at the end . during racing, gas is drained from the tank quickly : let's say 1 gal every 3 miles. i believe that vent is not enough
look at the gas cap gasket and draining hose. the gasket seems nicely sealing around the filler neck.i may leave the gas cap without its inner gasket when at the racetrack and let the excess gas flow down under the rear of car, far from exhausts.
or just remove the ball from the gas cap and enlarge the outer hole...
I would try it and keep an eye out for problems.
