AFB / AVS tuning tips

[Chryco Psycho]

These are very simple carbs to work on but actual tuning is made difficult by the lack of tuning parts available for them.  The Edelbrock carbs are very similar & use the same parts for tuning though

Step1 - Check the float level , this requires removal of the top of the carb , once removed invert the top & use a drill bit to check the distance between the top of the float at the end away from the pivot & the body with the gasket in place , Most AFB & AVS Carbs use a 7/32 float setting, the 383 avs seem to use 5/16 instead , with the EDDYS there should be a spec in the manual with the carb  , this should be checked even with new carbs as they can bend during shipping , bend the tab that touches the bottom of needle to adjust the settings. While you have the top off also set the float drop , this is the measurement from the top of the float to the body when the top is the right way up , there is a tab behind the needle that can be bent to adjust the drop , the spec for drop is 1/2".I have raised the float 1/16 or so when there is a bog as it will pull fuel in the airstream faster

Step 2 - reassemble the carb get the engine running & warm , make sure the dist vacuum hose is connected to the port 1/3of the way up the carb on the right side of the front of the carb ,adjust the mixture screws & get the car running as good as possible now take a manifold vacuum reading,  at idle , in gear if it is an automatic tranny, [you can remove the cap above the metering rod & watch to see if the rod stays in the down position at idle ] there is a spring under the metering rod which will need to be changed if the rods do not stay down at idle , springs are available in 3,4,5,7or8" increments & you need to uise a spring at least 1" below the vacuum reading you get.

Step 3 - adjust the jetting, take the car for a drive at a steady cruise & reasonable speed 30 mph + for 5-10 miles & using a new spark plug check the color you want tan -orange color  if it is Chocolate or darker you want to down jet,  if it is light orange to white you need to upjet . This not as easy as it seems , you need to remove the top of the carb & change both the jets & metering rods to move one step at a time , you will need the chart & the tuning kit part#1480  [Hopefully someone can scan the chart for us , hint hint] I have commonly found the Eddy carbs to run lean even with the biggest available jets installed , you may need to drill them with # bits to get enough flow I have also modified & made metering rods to try to get both steps correct [up position & down position]

Step 4 - Floor the car a dead stop up to the speed limit shut off & check the plug color again if it is darker or lighter adjust the rear jets the same way as the front jets

Step 5 - adjust the accelerater pump arm , by adjusting the rod away from the body you decrease the amount of fuel delivered , you want as little fuel delivered as possible  without creating a bog. if it bogs immediatley move closer to the body again, there are only 2 holes or sometimes 3 depending on the model of carb you have so you cannot adjust it much.
If it bogs 1/2 a second after the throttle is floored you will need a larger squirter which can be a problem I have not been able to get new ones of different sizes  but you can drill them with # drills & if you go too big you will need to solder the tube & redrill. You wil have to remove the top of the carb to get at the squirter

Step 6 - for maximum performance you need to adjust the rear air door ,on the AVS this is easy , you can undo the outer lock screw & adjust the center screw 1/4 turn a at a time counterclockwise until you can feel the secondaries bog as the air door opens  then tighten the screw 1/4 turns until no bog can be felt. With the AFB this is much more difficult, you need to remove the top of the carb again & remove the rear boosters & remove the air door , at the bottom of the weights you need to drill 2 holes [1 each side] & try the carb out if no bog is felt you can make a second hole 1 side at a time , or enlarge the first hole now you can either play chicken & say to yourself , it is better I quit or keep going until a bog is felt , at which point you either need to weld a hole back in or tap the hole & put a screw in to add weight again , my experience is that you can drill 2 3/16" holes in virtually any application & not bog after that it will depend how much converter & gear etc you have as to how much more can safely be removed     

[kawahonda]

The squirters are available and work for the AVS, just need to grind off the rear mounting hole of them since the Carter AVS doesn't use this hole for mounting. This may be better than drilling out the original.

https://www.edelbrock.com/accelerator-pump-nozzle-kit-includes-024-033-043-nozzles-and-gaskets-1475.html

[Chryco Psycho]

good call