revtothelimit - motorbike forum

Hi there, I have just bought a Yamimoto 50 for my daughter, she filled up the fuel tank and it immediately started leaking, a steady stream from what looked like an overfill pipe which then slowed after about 20 mins. The fuel indicator on the bike is saying that the bikes tank is half full. The bike is just over a year old, it's been regularly ridden. I was wondering is this a common problem, has the fuel tank just been overfilled? I've attached a couple of photos so you can see where the leak is coming from - any help much appreciated, thanks v much

No idea but that looks more like a siphon than a leak!

Just out of interest, does the flow change if you open the fuel cap?

What's going on with that tyre‽

Doesn't change when I open the fuel cap but I've been in touch with the manufacturer and they think it could be an issue with the fuel tank so going to have a look at that, thanks

Leoishere wrote: Mon Sep 15, 2025 9:31 pm Doesn't change when I open the fuel cap but I've been in touch with the manufacturer and they think it could be an issue with the fuel tank so going to have a look at that, thanks

Be intriguing to know what the issue turns out to be. I wonder if there's an internal tube that, if the fuel level is too high, fuel overflows into the tube. If the tube was bent, tipped over it'd overflow when part full. (I assume that's how these things work).

Never thought too much about tank internals. Wonder if an endoscope would reveal anything awry inside?

Count Steer wrote: Mon Sep 15, 2025 9:42 pm

Leoishere wrote: Mon Sep 15, 2025 9:31 pm Doesn't change when I open the fuel cap but I've been in touch with the manufacturer and they think it could be an issue with the fuel tank so going to have a look at that, thanks

Be intriguing to know what the issue turns out to be. I wonder if there's an internal tube that, if the fuel level is too high, fuel overflows into the tube. If the tube was bent, tipped over it'd overflow when part full. (I assume that's how these things work).

Never thought too much about tank internals. Wonder if an endoscope would reveal anything awry inside?

Yep, could be a split filler-cap drain tube. They're internal to the tank and could be cheap hose material that's weakened and broken.

If Rockburner is right and the overflow pipe runs inside the tank then its very likely that ethanol has eaten it through. If that's the case it should be safe to plug it up as near to the tank as possible. The other possibility, if its not fuel injected, is that the pipe comes from the carburettor float bowl and the valve is not seating. I would expect some symptoms of flooding in that case.