Had my bike die on me one day, long story short I’ve done a complete top and bottom end rebuild after encountering many problems with it

now I’ve tried to start it and it won’t run, the bowl(carby) fills with fuel but nothing gets past that point, my spark plug remains dry but as I spray some ‘start ya bastard’ through the air intake it wants to start and will for a second or 2 then it dies.
Before booking it in to a mechanic I want to ask if anyone has experience with a problem like this? Or if anyone has suggestions. TIA.