Is there a rule of thumb on difference between primary and secondary jets? The Holley on the car has 73 primaries and 80 secondaries. It's been running rich so I went down to 70 on the primary side and 76 on the secondary. The car has been down for awhile and I want to try to get it right before I fire it up.
There's not really a golden rule. If it was running rich I think dropping 3/4 jet sizes was probably a good step.
Speaking of Holley 4150's, It's usually about 10 sizes smaller on the secondary IF you are running a power valve.