prairiehotrodder wrote: ↑Tue Oct 17, 2017 4:39 pm
to start the tuning process on this set up i removed the rear jet extensions. Warmed up the motor and checked idle vacuum at about 6". I ordered a pair of 3.5 power valves. Stock is 6.5 on these carbs. Am i going in the right direction here? Idle AFR is about 13:1 on my gage right now. Shooting for 15 maybe? Then i'll play with main jets at the track from there on if it seems to be close at part throttle.
Brian
First: DO NOT SET the idle according to a AFR reading. Set the idle mix screws for best idle quality
once the car is WARMED UP ! Let it warm up.
Then set the idle mix screws. Carbed cars idle at a AFR that is richer than 14.7:1 EG : 12.5:1 or 13:1
This is Normal. Give it what it wants to idle the best.
Power valve: for the best idle quality without decay over time and to keep the plugs clean over time
use a power valve that is vacuum rated just lower than the vacuum at idle when idling in IN GEAR.
EG: if the manifold vacuum at idle IN GEAR is 6" use a 3.5" or a 4.5" rated power valve.
The AFR meter does not matter. What matteers is that the power valve is CLOSED at idle when idling in gear.
If consistant tune and plug life matters on this street driving car than this MATTERS.
Get it right.
A drag only car is not that critical but a street driven car that idles a lot MATTERS.
Check the vacuum idling IN GEAR. If it is 5" use a 3.5 or a 4.5 power valve.
Ignore this and expect shorter plug life and inconsistant car perf OVER TIME.
Let the car warm up and set the idle . Ignore the afr gauge at idle.
It wants what it wants. Idle quality will improve when you let it warm up.
With a tunnel ram that takes a little longer.
When the engine and manifold is cold keep the rpm up say 1500rpm to avoid fouling.
Let it WARM UP. then set the idle. it will idle all day at about 800-900rpm.
and near that in gear.
Now open the throttle to raise the rpm and WATCH the afr gauge. 1200 to 2000 rpm point>
" off idle transition" What does the AFR gauge say? You want it in the 14:1 zone at this rpm/throttle point
13's is good. The manifold must be warmed up. Warmer is better.
When you get it out and drive it you can check the PART THROTTLE cruise afr ( main jets) at 45+ road rpm.
14.5 ish+/- is good.
Anything below this road speed will be idle off idle transition until the point of primary main start up.
A Afr in the 14 range is good at this point. You can tweek the primary idle air bleeds to adjust this +/-.
If the power valve is OPEN at idle when idling in gear then eventually the tune quality will degrade
OVER TIME ( street driving time) requiring more frequent spark plug changing and fiddling with the carbs idle set up. What the afr gauge says is not relevant.
if you want it to stay clean and consistant get this right.
Let it warm up. During warm up keep the idle rpm UP.
My buddy with a tunnel ram uses a lil block of wood in the throttle linkage to raise the idle rpm during Cold warm up. (1500+rpm idle when cold)
WOT afr should be in the 12.5 to 13.4 is range at WOT.
Tune the WOT jetting for best track MPH not a preconcieved WOT AFR
But this is the range.
Again set the idle mix for best idle not AFR. Give it want it needs to idle best.
15:1 is way too lean at curb idle.