Modern Vespa

Hi good evening i am running out of ideas need help so i have a Vespa et4 125 on a 1999 year and this model ZAPM0400 and i am having problems starting first thing in the morning or if the bike has been standing for a few hour while at work during the day it takes ages it turns over fine and there is a strong spark and fuell getting to it things i have done

Replaced spark plug
replaced HT lead and Cap
checked Valve gap
replaced Carburetor (old one leaking all over the place) and adjusted mixture to about 2 turns open
replaced intake manifold
replaced auto choke
replaced auto fuel tap and pipe to carb

that is what i have replaced at this time it does not matter if you use electric start or kickstart it can take 5 to 8 minutes to start somthing a bit more i am so lost i do not know what to do this is my sons bike once started runs fine and then turn off and then starts fine please help thank you so much

That's not good enough to get the idle mixture correct. It's a good starting point though!

With the engine fully warmed up, adjust the idle mixture for maximum revs. Now decrease the idle revs to the slowest it'll run smoothly by adjusting the throttle endstop. Repeat to double check you have the best air-fuel mixture while keeping idle revs low and steady.

I recall someone here having a starting issue and it turned out to be the decompression system that's located in the valve system. I don't know the real name of this device nor could I find the thread to link it, but it controlled the compression at start-up and was malfunctioning.

thanks for replys the other thing i have notice is that when running the revs are going up and down not very much so not sure if that will add to the info i have given

thanks this could be a place to start but bit lost on where or how to sort