Optimal rpm -CIS vs EFI

[Phil Payne]

> I agree with Huw, though I am "mister EFI" myself, I respect what CIS is
able
> to accomplish completely mechanically, it is very brilliant.  I beleive
> reliability is a strong point of CIS, of all the fuel system related
problems
> I have come across on CIS cars, it has never been the fuel dist. itself,

I've seen quite a few metering head problems.  The device's main weakness is
the upper O-ring - when worn it produces unpredictable fuel flow at large
plunger depressions - the symptom is recognised by driving at a steady speed
on the flat and making a series of accelerator depressions.  If the car's
reaction is significantly different on several occasions, this O-ring is a
likely culprit.

The lower O-ring often leaks on older heads, but this is very rarely enough
to be a problem.  I've only seen one case of a car that lost residual
pressure through the metering head.

In the above discussion, I don't regard the system pressure regulator in the
side of the older style metering heads to be part of the device,  That thing
DOES cause problems on a fairly regular basis - and I suspect the culprit is
usually dirt.  Audi's "Kit of parts for metering head" is relatively cheap,
so if I go in there on a cleaning mission I usually fit a new spring,
O-rings and shims out of the kit.