proform race carb / Idle trouble

-
Well I am back at it! I had it sorted out last year by putting smaller idle air bleeds in it. Then I went and put a slightly bigger cam in it and the problem is back. I will be putting a vacuum gauge on it this week to see if I need to change the PV. For the curious ones, I put a Comp cams version of the .509 lift (.543 with 1.6 rockers) 292 duration in it. She runs good at full throttle. She is just terribly lean while cruising (throttle about 1/8 down). I've got to bump the throttle to squirt more to richen it up while cruising.
 
i encountered this lean idle in the 1968 AVS carb on the 340s and 440s. it comes from the EPA emission stds. on the carter and edelbrock carbs are easy to fix. a set of drills #61 to #80 is what you need. i have taken the idle jets out of holleys but is NOT easy. but only take out .001" at a time.
 
larger number pv is needed. the cruise vacuum is keeping it closed to long. a pv closer to the cruise vacuum will open sooner when the signal starts to fall. let's say you have a 3.5 pv and you have 12 lbs off vacuum at cruise. when you crack the blades open the vacuum starts to fall off but because the pv is at 3.5 it take longer for vacuum to fall off to under the 3.5pv to open it up.
 
Does this carb set Idle with the secondary butterflies?
 
You must log in or register to reply here.
-

Back
Top