Sanya SR125 carb problems...

Advice happily received! I am currently helping a friend who is getting into biking on a budget! He has been offered a Sanya SR125 for £200. Its been stood up for 4 years (its only 5 years old!!!!) and has only done 1800 miles. It was a non runner but we agreed with the owner a £50 deposit to allow us to take it away and see if we could get it to run. So after a few hours of playing it starts, runs, all key electrics work (starter motor and indicators need investigating) but after giving the carb a really good clean (including all jets out) and new fuel, it is still bogging down when rolling on from idle to 1/2 revs quickly. A gradual increase allows it to rev cleanly and at all points on the rev range it runs really nice. Interestingly if the choke is in 1/2 open it will rev through OK. The key points to note are as follows:
Changing the mixture screw position does not really alter the problem
Above 1/2 revs the bike will pick up on a rapid throttle open clean, the problem is only from idle to 1/2
The carb - this is where it gets interesting! The slow idle jet in the float bowl and the air screw are off set by about 7 mm although in the main throttle body their are two air holes, one directly above the jet and one above the mixture screw. If you put a piece of fine wire up through the jet housing it appears to hit a "step" and if you hold it to the light you can not see anything BUT of you blow a high pressure air line thought it BOTH holes in the main carb body exert air 9and I also filled it with duck oil as a tracer and this came out of both holes)

My immediate impression is that the hole above the jet is still blocked due to the presence of no light and a piece of fine wire not passing through

Would appreciate other peoples thoughts ?

Carb is marked as a Dekni Pz26 YB40NE18

Rob