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Discussion Starter · #1 ·
I seem to have a pinhole leak somewhere in the bottom of my fuel tank. I suspect it is coming from where the thin line connects towards the front of the tank. does anyone have a good way to locate pinhole leaks?
 

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Pressurize the tank and apply soapy water to the outside area you suspect of leaking just like you would a leaking tire. It will bubble at the leak. I might also add, that when I say pressurize, just a few psi is all it should take. I use a mighty vac brake bleeder to vacuum/pressure test a tank.
 

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^^^ that. Put the cap on, attach some tubing to the fuel outlet, invert the tank and submerge it in water, then blow in the tube. Watch for bubbles.

Are you sure it's a leak in the tank metal and not leak f around the outlet fitting?
 

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Discussion Starter · #4 ·
I'm not exactly sure where the leak is at but I've been finding fuel around the edges of the gas tank. I went ahead and filled it with hot water hoping the heat would expand the hole a little bit to make it easier to find I have a sitting on a cardboard box right now and I'm looking with a flashlight but so far I don't see anything. I'll let it sit for a little while and keep checking. I don't have a compressor or any way to pressurize a gas tank I also don't have anything big enough that I can submerse the tank in to try and find air bubbles.
 

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I've owned and ridden 60-72 BSA's for a lotta years. On the later ones, if you don't have a little seepage, you're outta gas.
If you have, or know someone who has a compressor and a regulator you can connect the tank's fuel outlet to a pressure source of just a LITTLE positive pressure and find it with soapy water. I do this on tanks I build but I have a large utility sink I submerge the tank into. The cap is obviously going to leak some but you can run enough into it for a positive low amount of air pressure.

DO NOT waste any money on CREME brand sealer. I've had good luck with a brand called KBS but plan on a whole day to do it. Tumble the tank in the clothes dryer with a handfull of 1/4" nuts inside. Wrap the tank with lots of blankets and run it on cool. Clean with plain soapy water and dry it, then dry it some more.
 

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Shop vac....

Plug fuel and vent holes and use the outlet side of a shop vac to pressurize the tank. You can just keep wrapping tape around the outside of the hose until it fits snug in the gas cap hole. It doesn't have to be a perfect seal. Then spray a dish soap solution on the outside of the tank and look for bubbles.
 

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I'm not exactly sure where the leak is at but I've been finding fuel around the edges of the gas tank. I went ahead and filled it with hot water hoping the heat would expand the hole a little bit to make it easier to find I have a sitting on a cardboard box right now and I'm looking with a flashlight but so far I don't see anything. I'll let it sit for a little while and keep checking. I don't have a compressor or any way to pressurize a gas tank I also don't have anything big enough that I can submerse the tank in to try and find air bubbles.
Sure you do! Put the tank in the cold (colder the better) for about 20 min. and seal the openings tightly. Bring it in to a warm area and lay it upside down and while it warms, spray soapy water along the bottom seam. Expanding air will come out of your leak causing a bubble. A seam leak is common on these older tanks.
 

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Discussion Starter · #8 ·
I don't have a shop vac or an air compressor. I do know it was seeping around the bottom edges of the tank with only one gallon in the main tank. with only one gallon in the main tank the pressure from the fuel was enough to cause the seepage. Now I have the tank completely full of water and I don't see any seepage yet.
 

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Sure you do! Put the tank in the cold (colder the better) for about 20 min. and seal the openings tightly. Bring it in to a warm area and lay it upside down and while it warms, spray soapy water along the bottom seam. Expanding air will come out of your leak causing a bubble. A seam leak is common on these older tanks.
^^^^ Genius!!!! Just don't seal the tank until after the 20 min. and before exposing it to the warmth. (if you seal the tank before exposing it to the cold, you won't like the results!
 

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Discussion Starter · #10 ·
I shouldn't need any pressure for it to leak since only one gallon of gas in the tank was enough to leak. now I have it completely full with water and nothing is leaking yet. it's close to 50 degrees here today and I only keep my thermostat set at 63 so I don't think that's going to be enough of a temperature difference to cause pressure.
 

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I shouldn't need any pressure for it to leak since only one gallon of gas in the tank was enough to leak. now I have it completely full with water and nothing is leaking yet. it's close to 50 degrees here today and I only keep my thermostat set at 63 so I don't think that's going to be enough of a temperature difference to cause pressure.
Where's your sense of ingenuity? If the wife's not home, empty out your freezer!;):mrgreen: You know, these aren't just household appliances!
 

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Discussion Starter · #12 ·
what I don't understand is why it will leak on the bike with only one gallon of gas in there but off the bike completely full of water and not so much as a drip.
 

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I had a pinhole in my tank a few weeks ago, and I just coated the inside of the tank with the POR15 motorcycle tank repair kit. Worked like a dream! No more leaks!
 

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Discussion Starter · #14 ·
I had considered cpaying the inside of the tank. The problem is the previous owner already coated it with something and I don't know what they used and I don't know if coding it was something new would be compatible.
 

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I would just blow into the small hose on the tank and use a soapy spray to find the bubbles.

Water might not pass through the hole due to surface tension or a hydrophobic element around the pinhole. Maybe a water wetter would change that?
 

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Discussion Starter · #16 ·
are you thinking that fuel might leak through but water won't?
 

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Discussion Starter · #18 ·
now I have it filled with gas and still no leak. for some reason it leaks when I have it on the bike but I can't get it to leak off the bike. I can't believe that are the pressure building up because when I had it filled with water with the gas cap closed as soon as I turned it upside down water came out from the gas cap.
 

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Of course. You're surprised at this? If you put the tank on, fill it with gas and take it to a mechanic, it won't leak there either.

The pressure test is a good way to test if it has a leak. Maybe it's just coming out of the cap?
 
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