Datsun J18 motor problem

Friends of the forum step to describe my problem. I have a Datsun J18 1800cc engine, what happens is that minimal (idle) run only two cylinders No. 3 and 4, and on top that is to say accelerated the four cylinders work .. I have reviewed the compression and it is quite good 160 psi, I also reviewed spark plug wires, platinum, condenser spark plugs of the carburetor emptiness hoses. I hope you can help me ..
Atte.Darío Muñoz