1975 Yamaha RD 350 unrestored

This is my 1975 Yamaha RD 350, running on 27.5 Pilot jet, 150 main jet, needle clip position 4(2nd from bottom), air screw 1 1/2 turns out and timing set at 2mm BTDC. The oil pump works fine but leaking so currently premixing Castrol Power RS TTS 2 stroke fully synthetic oil, seems good to me with less smoke. Does anyone hear any unusual engine noise? i feel there is a noise in piston? the bike usually starts first kick, should i turn the air screw to 1 3/4 turns out? the oil pump and its connections are still there, does it pump air as the oil tank is empty now? Can anyone give a rough idea how much it'll cost to restore(painting, including frame paint, and chroming) with no engine work? Thank You.