Gas leak after topping off

Good day, this morning we were going to go for a rather long jaunt in the 120. I went by the local dispensary that sells the 92 octane non-ethanol which I exclusively use in our older vehicles. I filled it up completely. Not to Where it was visible in the filler neck, but the tank was plum full. Upon driving away, there was a very strong fuel smell. When I parked a few minutes later to investigate,I noticed gas dripping from the fuel tank area onto the ground. I pulled the spare tire out and noticed the curved section of the tank on the upper part was very wet with fuel. I siphoned off about 4 gallons and I’m now aerating it very well. Anybody experienced something similar upon “topping off“.

Thanks in advance! Mark

Before you panic check to see if the filler hose can benefit from a little tightening.

Roger that, will do.

Found the culprit. I changed the sender a few years ago and the screws that hold it to the tank needed tightened. I think I’ll pull it apart and seal it up with some goo. Any recommendations?

I was going to guess the tank vent hose.
Mine once had a loose hose clamp. I looked around for somebody else to blame, but they were all hiding. :wink:
The usuals sell rubber gaskets for the sender, which is what I use. If your sender face is not flat you could add some fuel proof sealer from Permatex or a competitor.

When you take the screws out note if they go into a through hole or a blind hole and if the washers are sealing washers or split lock washers.

They are a through hole. Use sealing washers, not split locks.

Hi Mark,
I chased this problem on my 120 FHC and had no success in sealing the threads on the through holes on my replacement gas tank. I also had no success with a rubber gasket that swelled up and expanded and contributed to the leak. After a couple trys I purchased small O-rings to go under the heads of the screws, and used a composite rubber/cork gasket for the sender. This has sealed the sending unit and I no longer have to worry about overfilling my gas tank and loading up my garage with gas fumes and dripping gas. Here is the link to the O-rings I bought from McMaster-Carr.

Oil-Resistant Buna-N O-Ring

1/16 Fractional Width, Dash Number 006

When filling original gas tanks they spit gas from the overflow tube at the top of the filler well for some unknown reason, warning you that the tank is nearly full. My replacement tank does not, so I have sometimes filled it past the height of the depression that the sender is mounted in, resulting in that depression filling with gas and making a mess. Hopefully I have fixed this problem, so far so good.

Tom Brady

Hi Tom, thanks for the response and the tip. I got some Perma Tex 2 and I plan on removing the sender anssymbly and putting the sealant under the rubber gasket and on top of it, and then putting it back together. I’ll order some of those O-rings you recommended. Thank you again!

Arlington, Washington

One last comment on this item. As per Tom’s suggestion with the O-rings, I ordered some from McMaster. They come in packs of 100 at the exorbitant charge of about five dollars. If anybody has a need for some, I will have 94 extra ones. I think I could spare a few. Just send me an email with your address.