Fuel Leak Part II - Completely stumped.

[Parminio]

So I once again have the bike running great, handling great and braking great but I can not for the life of me find out where this fuel leak is coming from. I'm at my wits end. I'm beginning to think it's the gas tank itself, that it somehow has a hole in it.

For the record: it's is mirror finish clean on the inside. Not one spec of rust anywhere.

Looking up top at the fuel filter and line to the tank, everything is bone dry:



Something I did notice that was that it was rather wet in the cup around the gas cap. I knew I had spilt a little bit of Seafoam when I added it, but I don't remember spilling that much of it. So I pulled all that off and it looks a little suspect. There's some moisture all around where that cup goes over the snout on the tank. The red outline is where it's moist. It's bone dry on the passenger side (the high side when it's on the kickstand).



I also noticed that the gas cap seal was soaking wet with gas. I've never really paid attention to it until now, but I don't recall ever seeing it that way before.



So now we come to the actual dripping I can see happening in real time. Here's a short video I did of two drips. I then stood up to do a quick once over of the top area so you could see how dry it is, so the gas can't be coming from there.



So on this picture, those drops land on the back side of this area, then follow the frame down and wind up dripping off right where you'd expect a leaking clutch slave to be dripping.



And here's how much gas has leaked out of it since last night - probably about 3 ounces. There are other very small spots that have dripped off before it got to that point, but the spots are so small (about the size of a quarter) I don't think it's really that much more.



Here's the best shot I could get of the front side of the tank (you actually get a better look at it on the video if you go full screen). The wetness seems to go about half way up. It goes almost all the way across but seems to be a bit heavier on the "driver" side of the bike.



I am at a complete loss.

Thanks in advance for any advice.

 

[Spyglass]

I bet it's leaking from that seam weld between the two halves of the tank.

 

[Parminio]

I bet it's leaking from that seam weld between the two halves of the tank.

That's what I'm afraid of.

I've never heard of that happening before though.

 

[Parminio]

I went up to Harbor Freight and bought a gas can (both mine were full already) and a siphon pump and pumped 2 gallons out of it.

I'm going to give it an hour and see if that stops the dripping. If it does, I guess I'll need a new gas tank.

 

[Parminio]

Yep. Stopped leaking. It's gotta be the tank.

 

[Fire-medic]

You might want to do some poking w/an awl or other somewhat pointed object where you suspect the leakage is. You may find the weak spot. You could also pressurize the gas tank with several p.s.i. to see if you can then spot the point of leaking visible to the naked eye.

 

[Parminio]

You might want to do some poking w/an awl or other somewhat pointed object where you suspect the leakage is. You may find the weak spot. You could also pressurize the gas tank with several p.s.i. to see if you can then spot the point of leaking visible to the naked eye.

I don't have an air compressor.

I think what I'm going to do is pull the tank and take it 'round to a radiator shop and see if they can test / fix it for me. If they can't fix it, hopefully they can at least verify that it's leaking and I'll buy another one.

I hope they can weld it though. It would be just my luck I'd pay for a new one, get it installed, and it would leak in the exact same place.

 

[Redrum]

dup of my below post,

 

[Redrum]

I've fixed pinhole leaks with fiberglass cloth/resin. My 3 wheeler is going on 20 years with no leaks after a repair.

For cars I've seen shops wrap the entire gas tank in fiberglass.

 

[Parminio]

Not sure I'd ever do something like that. If it is leaking along that seam like I think it is, I'd have them weld it. If they can't, I'll just buy a new one.

 

[Redrum]

Not sure I'd ever do something like that. If it is leaking along that seam like I think it is, I'd have them weld it. If they can't, I'll just buy a new one.

Your money. Just get a NOS piece. Better yet a new bike. New is Better!

Don't do something easy and cheap that works.

 

[Parminio]

First off, I have no experience working with fiberglass although I do know a bit about it.

Secondly, fiberglass doesn't adhere very well to steel and it doesn't hold up to gasoline very well either. It takes special types of resins to make that work, along with the know-how that goes with it that I don't have. You can't use polyester resins at all as gasoline will go right through it in record time. Even most epoxy resins have issues with gasoline, which is why it's not used as a fuel cell on boats where it would be incredibly easy to do so.

Thirdly, I'd rather have a radiator shop that has decades of experience and know-how repair a gas tank that holds the equivalent of 42 sticks of dynamite that sits right under my ***, than me with no experience taking a stab at it and screwing it up and blowing myself clear to ******* Mars to save a couple hundred bucks.

But you do you, pal.

 

[Dansmaxresto]

When I got my Vmax back I just replaced the tank instead of spending hours cleaning, sealing, etc, then have the potential of it not sealing properly. So if you have the means just buy a new one and be done with it. I paid a little over $400 for a brand new one.

 

[Dorney]

I bet it's leaking from that seam weld between the two halves of the tank.

I agree with you. Gas will also wick to a certain degree that's why it's not wet just at the seem.

 

[Spyglass]

I think what I'm going to do is pull the tank and take it 'round to a radiator shop and see if they can test / fix it for me. If they can't fix it, hopefully they can at least verify that it's leaking and I'll buy another one.

If you end up buying a new tank, consider getting one of the plus-sized ones available.

https://www.v-max-f-maerz.de/vmaxkatalog/750_en.html
http://www.exactrep.com/acatalog/touring.html

Morely's likely has a clever setup for you as well: https://morleysmuscle.com/

 

[Fire-medic]

How times change. Last NOS tank I bought from a dealer was $205.

Parminio you can use a bicycle pump to pressurize the gas tank, just fit a schrader valve somewhere, like at a blank-off plate for the gas sensor electrical unit. You only need 4 psi to show where the leak is.

You can use something like this Fernco rubber cap which is rated for 4+ psi pressure, to seal-off the tank fuel inlet, replacing the tank cap. The O.D. tank neck is just-over 2"
https://www.acehardware.com/departments/plumbing/pipe-fittings/plastic-fittings/4873147



A weeping seam can be fixed by any competent welder used to doing such repairs.

Another plumbing piece useful for when you're working on your intakes is this Oatey PVC blank-off plate, which happens to be a perfect fit inside the carburetor/Vboost rubber donuts. They sell for < $.50 each.

 

[Big"A"]

So I once again have the bike running great, handling great and braking great but I can not for the life of me find out where this fuel leak is coming from. I'm at my wits end. I'm beginning to think it's the gas tank itself, that it somehow has a hole in it.

For the record: it's is mirror finish clean on the inside. Not one spec of rust anywhere.

Looking up top at the fuel filter and line to the tank, everything is bone dry:

View attachment 93532

Something I did notice that was that it was rather wet in the cup around the gas cap. I knew I had spilt a little bit of Seafoam when I added it, but I don't remember spilling that much of it. So I pulled all that off and it looks a little suspect. There's some moisture all around where that cup goes over the snout on the tank. The red outline is where it's moist. It's bone dry on the passenger side (the high side when it's on the kickstand).

View attachment 93533

I also noticed that the gas cap seal was soaking wet with gas. I've never really paid attention to it until now, but I don't recall ever seeing it that way before.

View attachment 93534

So now we come to the actual dripping I can see happening in real time. Here's a short video I did of two drips. I then stood up to do a quick once over of the top area so you could see how dry it is, so the gas can't be coming from there.



So on this picture, those drops land on the back side of this area, then follow the frame down and wind up dripping off right where you'd expect a leaking clutch slave to be dripping.

View attachment 93535

And here's how much gas has leaked out of it since last night - probably about 3 ounces. There are other very small spots that have dripped off before it got to that point, but the spots are so small (about the size of a quarter) I don't think it's really that much more.

View attachment 93536

Here's the best shot I could get of the front side of the tank (you actually get a better look at it on the video if you go full screen). The wetness seems to go about half way up. It goes almost all the way across but seems to be a bit heavier on the "driver" side of the bike.

View attachment 93537

I am at a complete loss.

Thanks in advance for any advice.

I would try to seal the tank with the white coating sealant. Might take care of any small holes in tank. Then I'd remove and check all hoses too see if they are leaking. See what that gets you

 

[Parminio]

I would try to seal the tank with the white coating sealant.

Sean Morley told me about that but I started reading up on it and it's pretty involved with multiple rounds of treatments and the like.

That's a service the radiator shop offers and they guarantee it when they can't weld a tank or if it has a lot of rust/contaminants in it. I still have to get it over to them to find out what's what.

I'm at the point that the tank is "floating around" in the frame but I can't seem to get it out. Reading the uninstall thread trying to figure out what I missed.

 

[Dansmaxresto]

I do remember removing my tank was a giant PIA!!

 

[Parminio]

$175.00

That's what it's going to cost. They'll strip the paint off it, pressure test it, re-weld the seam to seal any leaks they find and repaint it.