I have a 76 R90 motor that has new rod bearing and the small end bushings have been replaced and sized to the wrist pins. The motor has 40mm Bings with 170 main jets, 45 idle' 2.68 needle jets and I'm running W5DC plugs and the look perfect on a crank fire ignition with 26 degrease full advance. The noise sounds like it is coming from the center of the motor. The main bearings have about 30K or so. Oil pressure is between 30 and 80 pounds. The motor sat for 10 years. The noise happens at low to mid RPM under load only while lightly accelerating above 170 degrease.
Any ideas on what the noise might be?