Modern Vespa

Howdy. Came back from a 2-week vacation to find, not a real puddle, but a flat, thin spread of fuel on the garage floor. I'd had some drips before that which seemed to be a function of fuel spitting forward into the air cleaner during operation, and I got the impression that this was not abnormal.

But this was a greater volume of fuel. I noticed that I had left the fuel lever in the "on" position, and remembered that that could also sometimes allow leakage. So I turned the lever to "off" and hoped that would solve it. By the end of the day, most of the fuel had evaporated, and I figured I was fine.

Next morning, there was fuel on the floor again. I had left the tank pretty full before vacation, but checked and noticed it was way down. Hmmm. Found out just how far down when I went on an errand and the bike died at the end of the block. The tank had drained exactly to the height of the "reserve" tube. Don't know if that was significant, but that's the case.

So here's where I'm at: I pulled the tank, and there's no evidence of a leak at the tap or either end of of the fuel line—everything is is bone dry, and the fuel line is new. There IS evidence of fuel in the air cleaner—I can see the liquid shine with a flashlight—and at the bottom of the well. And I can't find any sign that it dripped again last night, when the fuel was below the "reserve" tube.

Any thoughts about what's going on and how to fix? Carb float? Has anyone ever encountered a leak that only occurs if the fuel level is ABOVE the reserve line?

Thanks for any advice.

Could be a worn fuel tap lever gasket. The one inside the tap, not the one between tank / tap; and/or a worn float needle seat. A full tank can cause a gravity drain, from the weight of the fuel pushing down against the needle seat. If the tap gasket is worn out, fuel will slowly run down the fuel line; even in the off position.

Why not both?

You need to replace the float needle for sure. That's the fundamental failure. A properly seating/sealing float needle can be left with the fuel tap on indefinitely and it won't leak.

And since you're ordering parts, the fuel tap "four-hole" gasket is another two bucks, so you might as well splurge and order one of those while you're at it. The hardest part of replacing it is not stripping the fuel tap screws while you're trying to remove them.

Many thanks everyone. Big wet spot again this morning. About to go at it and see what's up. Merci.

This is the way.

So, I just opened everything up and stared a bit (please keep in mind I'm kinda new to Vespas. Played around a fair amount with Dual Webers, but never worked with one of these (shbc 19/19)).

Also, everything on here is new, as of four months ago. New carb, new tank, new tap, etc.

There was no evidence of any fuel leak near the tap. Totally dry on the outside. When I opened it up and looked at the four-hole dingy, everything looked perfect.

Took off the bowl and the float seemed fine. Didn't seem to be binding or stuck. I DID notice that the rubber-band-like 0-ring gasket that fits in a groove at the top of the bowl, and seals against the base of the carb, was out of its groove and pinched at one point. Occurred to me that, if the bowl was overfull, or even when fuel was just splashing around while riding, fuel could drip out of there.

Took off the float needle and it looked perfect. Like brand-new.

The thing that puzzled me is that the only place I see wetness near the carb is INSIDE the air filter. It's really wet in there, from the opening where it attaches through the filter and into the bottom of the air-filter case. Eventually it drips out of there into the well, and from there onto the floor.

So, somehow, fuel is going FROM the carb INTO the air filter. I've been told that a bit of that is normal, but I'm thinking that could only happen when the engine is running, and the few drops in there work their way out and drip on the floor overnight. What's happening now is different. I probably lost a half a liter onto my shed floor while the bike was just sitting and I was away for two weeks.

Maybe there's more than one thing going on here. Maybe the carb spits forward a bit when I ride, and I get a couple of drips from that. And maybe I had some sort of bigger leak when I was away. I haven't been able to identify it. Will order a re-build kit and see if that helps.

And I'll go test the tank off the bike with the fuel tap in, over a bucket, and see if there are any leaks overnight.

Any thoughts appreciated. Onward!

Some fuel spit back from the carb is normal while running, but something else is definitely going on. Testing the tank over a bucket is a good idea. The float bowl cover gasket being tweaked could be a contributor, but it still seems like alot of fuel being lost (while you were away).

Well, progress. Maybe.

The tank and tap, sitting over a piece of cardboard for two days, showed no signs of leaking. No marks on the cardboard.

But when I added the carb, there were a couple of drips overnight. Seemed to be coming from the banjo fitting (if that's what it's called? Where the fuel hose attaches?). No dampness where the hose itself connects. I'm thinking it's a leak around the edge of that fitting. Kinda makes sense because fuel is sitting behind it, yes?

I'm thinking I'll spread some light sealer on the outside edge of the fuel screen behind the fitting. Maybe it will seal better and stop the leak??

Occurs to me that this would explain why there's a leak even if the tap is closed. At that point there's still fuel in the line, and gravity is pulling it down.

Eh? Er? Or am I nuts? Tell me the truth. I can take it. I think.

Does it have the fiber washer that goes behind the bolt that holds the banjo fitting on?

Does it have the fiber washer that goes behind the banjo fitting to help seal it up?

I'd also recommend at least one of the wire hose clamps to put some pressure on the fuel line where it slides over the banjo fitting.

Okay. Mea culpa. After all this, it seems to just be my dumb error: All the black rubber hoses in my old VW have clamps, of course.

But when I got the translucent green vinyl hose for the Vespa, for some reason I assumed it was made to just slip on and hold tight without a clamp. It was a tight fit, the material is stretchy, and I worried that a hose clamp would cut into it. OOPS.

Clamped it and, uh, no leak for two days. Assuming it leaked even more when the tank was full and the fuel lever was open, that would account for the significant loss while I was on vacation. And why it leaked less when there was less fuel in the tank (less pressure in the hose).

Thanks everybody. I keep joking with my friends that my method of learning is to make every possible error, so that, eventually, the only option left is to do it right.

Won't be making this particular mistake again. Merci.

(Now to figure why there's a significant drop under the oil filter in my Ghia . . . )

You're gonna be right at home here, I think.

It's the only way to do things as far as I know…

You may want to check inside the fuel tap where the holes are located. I had a similar problem, but it was leaking through the venturi orifice and into the engine.