PK50 Carb issue

Need some pointers. Pulling my hair out trying to get the engine running properly. Just rebuilt new seals and gaskets plus piston and the engine will not idle correctly. Replaced the carb with a new one and resealed the inlet pipe etc and cannot see any reason for the inlet system drawing air but the engine demonstrate all the signs of an air leak. The engine races on its own for a around 30 seconds at a time unprompted cannot get the idle to settle and have to constantly blip the throttle the mixture screw seems to make little to no difference how the engine runs. On rare occasions it will idle correctly but blip the throttle and the engine races again. The choke seems to act as a throttle and I can rev up the engine using the choke, is that normal, when the engine race it does nit seem to be running lean rather the opposite.

Run out of things to try any suggestions from any one 

Seems that you could have problems with the fuel supply...

Check fuel hose...wrong position or too long fuel hose can catch an air bubble.

Also check, if tank cover venting works well (try running engine without cover). So also check if there is no extra fuel filter somewhere in the hose. If yes, remove it.

Everything which stuffs the fuel supply can posssibly cause such problems.

Remember: when your engine is running, and you close the fuel supply, before dying,  the engine revs up for some seconds.

Got the picture?