Datsun J18 motor problem

Friends of the forum, I'm writing to describe my problem. I have a Datsun J18 1800cc engine. The issue is that at idle, only two cylinders, numbers 3 and 4, are firing, but at higher speeds (when accelerated), all four cylinders are firing. I've checked the compression, and it's quite good at 160 psi. I've also checked the spark plug wires, points, condenser, spark plugs, and carburetor vacuum hoses; everything seems fine. I hope you can help me.
Sincerely, Darío Muñoz