Tony Gordon was thinking out loud about a PI conversion and mentioned
that a pre-pump should fix the problem of an un-baffled fuel tank.
This is not the case. The baffles in the tank prevent the fuel
flowing away from the outlet, keeping a constant fuel supply available
for the pump. In a carby car, this is overcome by the fuel bowls -
they maintain enough fuel until fuel, once again, flows from the tank
outlet. With the high pressure pumps, both Lucas and Bosch, you need
constant fuel flow or you won't go! Even worse, if you suck air into
the system, you're going to have to bleed it (main cause of problems
with the PI system). I converted my '71 ex US carby car to PI and
tried to do it without a baffled tank - it doesn't work! A cheaper
and easier way to fix this problem is to fit a 'surge' tank of about a
litre capacity, in the spare wheel area of the boot (opposite the
filter is where I mounted mine). Run the tank outlet into the surge
tank then from the surge tank to the main pump (you can run it through
the filter on either side). My pre-pump is mounted before the surge
tank which also runs a return line to the top of the fuel tank. I've
crimped this line slightly so that I have positive pressure throughout
the system (about 1-2 lbs). This way GUARANTEES positive fuel flow at
all times to the main pump.
When you're looking at making your throttle linkages, may I suggest
that you look at running them from ABOVE the throttle bodies so that
they PUSH the butterflies down. The standard system runs below and
pulls on the butterflies. This, in itself is not a problem, but if
you intend to fit extractors, then you do limit the space available.
If you've got the chance, run them above and you don't ever have to
worry about space to fit those big bore outlet pipes! (ask me why I
know this.)
All the best in your quest - it will prove very rewarding - nothing
better than 6500 rpm and still going - can't do that with carbys!
John Mc
'71 TR6 PI
'76 Dolomite 1850
"Fast is First"
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