Ferrari 412 Idle Adjustment (CO and Air Bypass Screw)

I'd start with something like 1/2 turn open on the air bypasses (and some throttle plate open) just to get it running. Once it does run (and can warm idle), you would fully close the air bypasses and set the warm idle speed to something like 700 RPM using only the throttle plates (and have equal vacuums) and then open the air bypasses to get the higher warm idle speed (and still have equal vacuums) -- but why aren't you targeting the 1000 RPM warm idle specification?

The mixture screws are super-sensitive -- even 1/32 turn is a lot. At the final adjustment, it's a challenge to actually move it without moving it too much.

 

What Steve said plus set mixture at every step of setting idle speed. At very low air flow small changes in RPM will change mixture quite a bit. And to expand on Steves remark of mixture sensitivity it really requires an exhaust analyzer to adjust. It is just hopeless to try and do it by ear.

 

Not sure if 412 is any different than the 400i FI system. For 400i, the air bypass screw is a last resort and in most cases both should be fully closed. Bypass is only if one bank will not balance with the other using the throttle plates and then only one should be slightly open.
You need some kind of manometer to balance the two banks and a gas meter for CO. Dwyer makes some reasonably priced DP gauges; I made a water manometer and it is WAY to sensitive!. I have a Gas-O-Meter for CO. I just did a search and there seems to be a larger selection now for CO meters for car testing.

 

Your understanding of bypass screw adjustment is in direct conflict with instructions directly from Ferrari applicable to 512BBi, 400i and 412. And in fact every CIS injected Ferrari. The air bypass should be used for providing 25-30% of the idle air.
A simple vacuum gauge connected via a Y in a vacuum line attached to both intake manifolds. Pinch each line and adjust balance. Continue pinching and adjusting until vacuum gauge does not change when either line is closed off. When done throttle should be able to be rapidly opened a long way and snapped closed with no dip below idle. .

 

The warm idle speed should drop some, but it should keep running. How many turns does it presently take to close them (anything over ~1 turn is too much and shows that the throttle plates should be opened more at idle).

Those are really "tight"(lean) emission specs. If you don't have cats, you can run much richer. Even if you do have cats something like 1.0% CO (upstream of the cats) wouldn't be a disaster.

 

Big difference. I was taught by Ferrari. They changed the procedure to something that actually worked and improved driveability.

 

I use the only book I have. It works for me. Thanks 360.
Ken

 

They ran them very lean to pass various emission standards which even then existed in some countries outside USA. We were told unofficially to ignore them and run 1.5%.

That even applied to US TR's. The biggest difference to those was cold starts and running before O2's came on line. At 7/10s they were just miserable but with the aid of air injection to clean up the cold HC it got them into the US.

 

That's reasonable. You don't want the throttle plates hitting/binding on their bores at idle. Even if you set these a little much too open, you'll just adjust them down (and they need to be open enough to eventually get it to warm idle to make the final adjustment).

Can sympathize that it's difficult to know when something in the F documentation is "God's law" and when it's something that was just an initial best guess by them (or Bosch). The 400i and Mondial8 were the first F models with K-Jet, and the Mondial8/QV WSM has the same instruction to fully close the air bypass screw (but you can tell that they just copied what was in the 400i WSM as they wrongly including that note about "balancing" while the Mondial8 only has one plenum -- and, as a side note, all of the CIS information in the F documentation was obviously written by Bosch as the English grammar and noun choices are so much better ). The later F model documentation covering K-Jet and KE-Jet, and the aftermarket Bosch CIS books (e.g., Probst, Watson), all indicate that this set-up evolved (as Brian indicated), and they all have this scheme of most of the idle air going thru the throttle plates, but a small portion going thru the air bypass. When that 400i WSM was written, they thought that having the air bypass fully closed was the best way, and there's certainly no harm in doing it that way. This isn't some irreversible choice like picking a paint color for the coachwork. If you do it the 400i WSM way, and it works well for you = great. You always have the option of doing it via the later method if necessary/desired.