Hi Randall
I can assure you that there is no correlation between rpm and fuel flow,
there is a fixed end and a moving end to the fuel shuttle, the only control
for the moving end is by vacuum, more vacuum less fuel flow controlled by a
roller on a tapered wedge. The main thing is that with those six rather
large butterflies in the throttle bodies, you only have to touch the
throttle to see the vacuum vanish, even when driving there is little vacuum
unless on over run! I guess this may be how they made sure there was enough
fuel at higher rpm! Also please bear in mind that the
TR5 and Early TR6 (150) only makes 9.0" max except over run when it is 17"
TR6 (late) only makes 10.5" max except over run when it is 20"
2.5PI Saloon only makes 12" max except over run when it is 24"
Figures taken from the Lucas Calibration charts. I believe carb motors make
significantly more vacuum under normal driving conditions than this?
On the Saloon there is a vacuum reservoir for the brakes due to inconsistent
vacuum production so that you can stop the thing!
Graham.
----- Original Message -----
From: "Randall Young"
Subject: RE: PI
> Graham, I'm almost certain that the fuel flow remains relatively constant
> *per firing* as determined by the displacement of the metering pump.
> Otherwise, there would be a huge variation in mixture (from too rich to
run
> to too lean to run) from, for example, 2000 rpm & 10" vacuum to 4000 rpm &
> 10" vacuum. Since there would be roughly a two-fold difference in air
flow
> between those two conditions, there *has* to be a corresponding difference
> in fuel flow or the engine will not run.
>
> Randall
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