A lot of people will disagree, but I have found the Weber “best lean idle” adjustment to be a crock of crap. There are too many variables involved from engine to engine. That being said if you don’t have an AFR gauge it is helpful to start tuning. In my experience the “best lean adjustment” gives a too lean AFR of around 13.5 on the 3 engines I’ve tuned. The sweet spot for idle is 12.5-13.0 on my engines.I'm back on this thread to ask a simple question. I did look for an answer but didn't see it.
First, I have a Weber 38/38 with electric choke and the choke opens properly. All tests were done with the engine warmed up.
When tuning idle, I know the adjustment screw can tell you if you need bigger or smaller idle jets.
I believe the starting point for tuning is around 2 full turns from seated.
My question is...
When tuning, if you have to go 3.5 turns to start to smooth, do you need a bigger or smaller idle jet?
On the opposite side, if you smooth out at 1 turn, do you need a bigger or smaller jet?
If I turn mine in beyond 2.5 turns, the engine really gets jumpy and wants to die. I can't seem to get a difference on adjustment past 3.5 turns but it seems to need more than 3.5 turns.
If you are not having any changes in engine speed at 3.5 turns you are already too rich approaching 11AFR.
If the engine is jumpy below 2.5 turns you are too lean (this starts at 13.2-13.5 AFR idle with a DGAS).
If you are below 1 turn out you need to go down on your idle jet
If you are above 3 turns (2 according to Weber, but I disagree) you need to go up on your idle jets.