@Dimi, welcome here in this hive.
As Iahawk already said, it's sometimes nasty to get an old carb operational again.
Swapping jets is pretty easy, IF they are the same thread as the jet-stock. Has to be checked before.
There are not so many different thread sizes in this range of carbs, either 4 or 5 mm thread. Except pilot screw, its 6x0.75mm fine thread.
For carb testing, air intake hose off from carb.
Pls give us some pics of your new carb to see what we can do about.
Your "new" carb has how many small inlet pipes?
Pls see pic, is this exactely the carb you have?
-should be a 26mm CVK carb for 150ccm
-red arrow indicates fuel IN line, all other tubes there need not to be alterated
- the lowest, coming from bowl is the drain tube
---two others, shorter, support your idle and vacuum system
-you need a vacuum line between your fuel pump and your "intake " between carb and cyl head
This service set you show there is for a completely different kind of carb, a PWK-type, will not fit on any modern KYMCO.
Maybe this helps you to ....
https://www.kymcoforum.com/index.php?topic=31762.0