Modern Vespa

Please help me somebody... I am having problems with my scooter. Let me explain. 2 weeks ago I noticed that I was using a lot more fuel than normal... A trip to the mechanic revealed a tear in a yellow tube that he told me released gas on acceleration. He fixed it and off I went. The following day I started the bike fine, set off as normal, but about 500m from my house the engine gave up and died. I could start the bike but couldn't convince it to accelerate and any attempt to do so resulted in it cutting completely.
Another trip to the garage this time by pick up truck. A new battery and a cleaned carberator (?) and air filters as the mechanic said the engine was flooding. I left the garage, drove completely fine for a good half an hour before the problem started again. Not nearly as bad this time, but there is a definite loss of power and a reluctance to accelerate once the engine is warm and some time has passed.
What could be going on!? I've had the bike 6 years and never had this problem before.
Please help me!
It also feels a bit juddery at times too.

Valve adjustment, Vacuum leak, crap in the gas tank.

Thank you for the suggestions. Is there one culprit more likely than the other or am I better just to have the mechanic check all possibilities? I know absolutely nothing about mechanics so find myself at the mercy of whatever they tell me!
I'm quite nervous to drive it now since it gave up the ghost in a busy tunnel and I saw my life flash before my eyes so I'm praying that it can be fixed once and for all...

Sorry to hear about your bike issues! Welcome to this forum

I don't think your bike has valves, being a 2T two stroke.

Are you taking it to a Vespa dealer? It sounds odd that this isn't fixed after 2 visits.

Unfortunately, this one is probably difficult to diagnose by internet. As kz said, it can one of a few things. Just a few other ideas: dirty carb, a bad sparkplug or coil, a stuck float, low compression. I am sure it is solvable and probably simple, but you will need to investigate one thing at a time.

In a two-stroke engine the washing phase includes a perfect seal of the engine casings, this or one of the other explanations already given seems or may be the right ones; of course making remote diagnosis is complicated ...
Or also, try to change the spark plug cable, clean the tank by throwing away the gasoline and putting another clean one (there may be water in it), many things ... that's why the mechanic exists.
Welcome to MV from Latina, Italy.

I missed the 2T designation, sorry. Start with a new spark plug and clean gas.

Thanks for all the ideas everyone. I got the bike back today with some new cables and so far so good (I'm not sure exactly which cables though as I'm trying to do this in Spanish). Fingers crossed!!

agree on draining fuel tank and pulling fuel tap on bottom of tank, check for dirty filter screen, might change tap and fuel lines.

i suspect you might have a problem with your fuel tap...these are common failures on these bikes....you can tell if its broken by removing the fuel hose from the carb..if fuel flows out continuously without stopping, you need a new tap..

its probably just gushing into the carb and flooding everything....

if you take some pics that can help

So. I have had the bike back a few days now and it's running much better. However I am noticing that while it doesn't lose power and die completely like it was doing previously, it does have these little 'epsiodes' where the rev counter drops from 6000 to 5000 when Im riding it, but will then increase back to 6000 again. Is this normal? It seems to struggle at full acceleration and on the hill.