2001 Gas Gas TXT 280

[PatMc]

Evening all 

I’ve recently rebuilt the engine in the above mentioned bike and it starts and runs but there is a running issue. 
When it’s idling it seems to hold the revs just fine but if you give the throttle a blip at all, it seems to rev really aggressively and takes a few seconds to drop back to a normal tickover.

Also on initial start up if you use the choke fully open it seems to absolutely rev its knackers off .

I can tell it’s a fuelling/carb issue but unsure what to look for . 
 

Thanks in advance if any of you can help 

Kind regards 

Paddy