Ancient History

[RABBITT_Andrew at mv8.orbeng.com.au]

>> What I want to know, is what happens when you have radical
>> cam timing? This nice puddle of fuel on the inlet valve
>> gets blown back up the inlet duct when the valve opens?
>> Makes nice flames, if you don't run an air cleaner :-) 
>> But this surely can't make for repeatable fuel volume supplied
>> to the cylinder?
>
>As Ralph pointed out, the vacuum goes down at lower rpm due to valve 
>overlap. A vacuum responsive FI would make the mixture too rich for 
>the engine to run. I think carburators are more tolerant of this low 
>vacuum at low rpm because they are passive devices and because they 
>are less precise in fuel metering.

carbs don't use manifold vacuum to meter fuel.  All they use is the 
depression created by airflow through a metering venturi.