Modern Vespa

I would love to hear, from those mechanically in the know, an explanation of the following.

Recently my fuel pump gave out on my 250. A shop replaced it (price = ouch). In my first ride, the fuel gauge went down to 1/2 after only riding 25 miles! (I thought the gauge was off but that was not the case. I was getting piss poor mpg).

But at the next fillip, I got 38mpg. Still piss poor compared to my usual 59 average mpg. Then at the next fill up, mpg went up to about 45. At the most recent fill up, it's up to 55 mpg.

Just curious - can anyone tell me why it took few hundred miles of riding to get my mpg back to semi normal after a new fuel pump was installed.

they probably also reset the computer and the engine has to relearn the fuel injectors consumption again.

If this is real fuel consumption ( not just what the electronic gauges are telling you) then it is a serious concern. It is possible that dirt has got into the injector and preventing it from shutting cleanly and it is also possible that the fuel pump is wrong and delivering incorrect pressure. If the excess fuel is getting into your oil you will have even more problems. Check to see if the oil level has mysteriously risen and see if the oil smells like it has fuel in it.