Modern Vespa

First of all, let me say hi to everyone here. This forum has always helped me out so far to get things working when I couldn't figure it out on my own. You guys are awesome.
Now on to the problem. This is probably the last one, as everything else seems ok so far.

I've got a Vespa S50 small frame that I acquired recently from an owner that did not look after this beauty. After doing everything so far, which has mainly been cosmetic with some mechanical work, I get stuck at the starting part. I checked everything I could, and the problem is that it's not letting the fuel go from the tank to the carb. I've got a vacuum releasing the fuel normally, but it's not doing so. I've tried sucking trough the vacuum tube myself, and that releases the fuel. I tried doing this just before starting with the electric start, so it puts some fuel into the carb, and this starts the scooter right away. It only keeps going until the fuel in the carb runs out I'm guessing. After that it doesn't start until I do that again. I tried adjusting the screws on the carb but this doesn't seem to do anything. But to be honest, I'm not entirely sure I did that correct either, as I'm not 100% on what they do.

The air filter is not sealed around the carb. It's just put around it. Does this make a difference?

Thanks for reading this and any help would be seriously appreciated!

Most vacuum lines are mounted in the intake manifold which is between the carb and the cylinder head. If you are not getting vacuum, either the line is not good (small holes, cracks, etc), the port where the line is connected is clogged, or the intake manifold itself is not sealing properly - again, cracked, ripped, etc... You also have to have a good seal at the head and carb.. You may want to take the manifold off and give a good look over for problems. Usually if this is the problem, you have to flex the rubber a little to find the crack. The heat from the engine breaks down the elasticity of any of the rubber parts over time.Take your time and I will bet you find the source of the leak. Good luck.

There's usually more than one simple line connecting the manifold to the fuel tap (at least there is on the GT and GTS models). If there's a crack or a bad connection anywhere in these lines then you'll lose the vacuum. It's quite cheap (and relatively easy) to replace all the vacuum lines so I'd just do this. It might be worth seeing if you need replacement clips or T-connectors while you're doing this. If the bike is over 6 years old then I'd also replace the fuel line as well.

Hi mate,
If the scooter is a 2t then there is a manifold vacume take off, the vacume pipe that connects to the side of the carburettor is the 2t oil feed,
If everything is connected and there is no negative pressure you have an almighty air leak, DO NOT be tempted to fit a new non vacume petcock to get round the problem as without fixing the air leak i guarantee you WILL seize the engine.
If everything checks out and no vacume, you need to get the engine case pressure tested as the case seal maybe at fault.
Cheers Andy.
Ps the scooter will never run above 1/4 throttle if the airfilter pipe is not securly positioned on the carb bellmouth and airbox.

Thanks for the replies, everyone!

A little bit of a history:

the bike is a 2014 model. I've replaced both of the tubes from the fuel tank to the carb already. this isn't helping so far. I've secured them to the connection with cable ties, as that's what the vendor that actually sold it in the first instance, told me to do as it works just as well according to him.

I've taken the manifold off and checked it for any damage, but can't see anything wrong with it. there was a piece of metal in the filter after i take the manifold off, however. I've taken that out and still produces the same results.
As far as I can see there's no vacuum connectors on the manifold. there's 3 plastic tubes running to the carburetor. One very very thin one, and then the vacuum one and the fuel feed. all are connected properly as far as i know. I'm tempted to bring it into the shop to get it fixed, but won't know what the problem is myself

Left it overnight after cleaning out the jets one more time. Started it up this morning and it works!! It doesn't keep running in idle, but at least it's running now!

Thanks for the help!