Gilera runner sp 07 engine swap

Basically i have a gilera runner 07 with a 50cc 2 stroke engine in but unfortunately the bike runs but does not ride as there's something wrong with the engine, i was wondering if i was to buy a used piaggio engine e.g fly liberty etc on its own without the loom would i be able to re use the loom already in the bike for the new engine?
Also if i can re use the loom will the new engine need to be 2 stroke?

If i cant use the loom is there anywhere i can buy one?

 

You don't change engines just because it's not running right, you sort out the running.
Only time you condemn an engine is when it's completely shagged or stupidly expensive to repair.
Take it to a proper bike mechanic, not one of your mates who thinks he knows because he read it on the internet.
Apart from that, tell us what's going on with it and we'll try and help you along the road to a decent scooter experience.

 

Ive taken it to an actual mechanic and they cant find the problem how can you assume i just took it to a friend and left it at that.
The actual bike mechanic cant find the problem unfortunately as the engine they said the engine looks fine. The bike runs great when on the stand* but as soon as the rear wheel touches the ground the bike does not want to move even with half or full throttle the bike bogs out and shuts off.

 

We get a lot of people with similar problems, if you had elaborated your question to include all the information, we can answer better.
Is it carb or injection?
How long have you had the bike and has it been like this all along?
What work has been done already?
More detail helps loads.