jets and spark plugs

[krowbar]

Checked spark plugs and looks lean. I'm thinking of jetting the carb up and don't know if I should do all 4 or just the primaries. This is my setup.... Holley 850. No choke.with 80 jets front and back. Recent rebuild on carb new pumps,new baseplate,new 6.5 power valves new primary float.new open air cleaner assembly(had dual snorkel) 1/2" phenolic spacer. Idle mix screws about 1 3/4 out. Timing about 20° initial. Fixed overheating issue with new stat and radiator. Runs about 190°. Idles good. Runs good,except for a little flat spot past idle. All this on my 440 w/727.

 

[Meep-Meep]

You can try to jet up a little bit from the factory setting, but if you have to go way out of range then you need a smaller carb. Too much carb can actually cause a lean condition.

 

[krowbar]

You can try to jet up a little bit from the factory setting, but if you have to go way out of range then you need a smaller carb. Too much carb can actually cause a lean condition.

when I got the car the plugs were black. Replaced with same heat #. I was thinking that since I changed the air cleaner to an open housing(base and lid with open element) that it might be sucking alot more air than before. That's why I was gonna try upping the jets. I just don't know which set to raise or raise both sets.

 

[67 coronet]

start with just the primarys(fronts).once you get the lower end dialed in you can address the secondaries.unless you romped all over this thing right after your swap the problem is in the primarys.i am sure it was due to improved air flow as you guessed.

 

[krowbar]

start with just the primarys(fronts).once you get the lower end dialed in you can address the secondaries.unless you romped all over this thing right after your swap the problem is in the primarys.i am sure it was due to improved air flow as you guessed.

I did a few burnouts, but more on the road driving and idling to check the temp readings and new digital tach.

 

[Meep-Meep]

when I got the car the plugs were black. Replaced with same heat #. I was thinking that since I changed the air cleaner to an open housing(base and lid with open element) that it might be sucking alot more air than before. That's why I was gonna try upping the jets. I just don't know which set to raise or raise both sets.

Not likely the air cleaner made that much difference unless you are going from a small soda straw snorkel. Point is you don't require all the CFM for most driving. But if there is any question about the air cleaner, put the old one back on and see if the plugs go dark again. I have learned to never say never and to back up theories with scientific data.

To sort out a 4 BBL you should start by checking your WOT vacuum reading. Hook up a gauge to the manifold port and see what it reads when you mash the pedal on the way to max RPM. Of course watch where you're going and don't crash! Probably want to have a helper report the readings. The WOT vacuum reading you want is 1.5 in hg. If you are at zero you have too much carb and the circuits won't work properly. You need velocity and the proper pressure differential for a carb to work as designed.