Hello I have a 1983 12a BP with a Holley 600 double pumper, fuel pump, MSD ignition yadyadyad... I’m curious to know what the recommended jet sizes are for this type of set up. I’m also having an issue with the car where if I cruise for a while it will start to backfire and cut out which leads me to believe the the carb needs a clean and tune up. If anyone has any info or suggestions let me know thank you

 

so many things .. bad timing .. wrong size discharge nozzle.. wrong accelerator pump cam... wrong jets ... try 68 to 73 p .. and 70 to 75 s... don't like to guess like to kno get a wideband if you're serious .. anywhere from 13 to 13.5 wide open throttle is good.... a hav good luck with the pink cam screwed in the middle and orange cam in the first screw hole....get a holley tuning book .. search button is your friend ... good luck

 

for the primary, see what you have in the carb, and try the next leaner one, and see what it does, and then go richer and see what it does. ideally you'd start with the biggest jet you had and work your way leaner until it was happy. starting in the middle is hard because it acts the same if its rich or lean.

for the main jet, start rich and work your way leaner until it runs the best, and then go to the next richer size.

a wideband will speed things up, and obviously having the carb working properly is a must.