I looked at the air horn on the carb and found this number; 1850-6.
I looked up the carb on the Holley website and below is a list of specs for the carb
I ordered a set of jets and an accelerator pump nozzle a few days ago and today it arrived. I ordered the parts based on notes I had made about the carb. Well I had several different notes on the carb and ordered parts based on the earlier notes.
I removed the accelerator pump nozzle and found that the size is 25 = 0.025".
The pump nozzle I ordered is 0.033". That is a significant change. So I need to order several sizes. I will order these two sizes, 0.028" and 0.031", and see how the engine runs and if that takes care of the off idle stumble.
Also I in the same purchase order above, I ordered a pair of 66 jets. Turns out that 66 jets are installed. So I will be ordering a pair of 64 jets and 68 jets.
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Carb Specs
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Primary Jets
Stock = 66
Installed = 66
Secondary Metering Plate
Stock = 39 PLATE*
Installed = 39 PLATE*
Pump Discharge Nozzle
Stock = 0.031
Installed = .025
Power Valve
Stock = 65
Installed = 65
Secondary Diaghram Spring
Stock = plain
Installed = plain
