In the 20 years of ownership w
In the 20 years of ownership with my 365BB, I've never been particularly pleased with two distinctive running characteristics of the car.
Specifically, driveability when cold...and,
Although I have many years of tuning experience with Webers and high-performance engines, I always accepted the "folklore" that that's just the way the early BBs run..and that the problem is typical with the Webers. I cannot discount, even for a brief moment, that the tuning phase related to the classic Weber transition can be a real bear to resolve...I had presumed, until very recently that Ferrari had made their best attempts to jet these cars properly.
However, after much re-reading of several old Weber technical manuals...and comparing their suggestions for tuning with what Ferrari specifies for the proper idle mixture setting, I came to the realization that the idle mixture/slow running jet is just too small.
Virtally all technical references specify that if the car is jetted properly, the slow running screw will be out from 1.5-3.0 turns maximum, presuming that there are no throttle shaft leaks. On my car, the best idle quality is achieved at 4 + turns out. With the mixture set that way, the car stinks at idle...and stumbles on part-throttle tip in. Looking carefully at the pitch on the idle speed screw and the depth of the "mixture hole" in the carb body, you're pretty much out of adjustment with the screw out at 4 turns.
So...I ordered a set of idle jets one size larger than stock (.50mm->.55mm). After installation, I re-adjusted the idle mixtures (now at 3+/- turns. The idle speed had jumped to 2200 RPM!
-Cold driveabilty dramatically improved
-Unburned HC smell virtually gone...
-Stumble....What stumble? 99% gone
-This is the best the car has EVER driven
-Almost docile, around town (really)
All said and done, the best $60 I ever spent on this car!