On 27 Oct 1994, A. B. Bonds wrote:
> I an currently rebuilding the HIFs because I can't stand the sight of
> abused machinery. I am debating whether to try and re-install them.
> In your article you alluded to proper set-up. I was wondering if (a)
> you had any hints in this regard beyond the normal SU lore (I have
> set other types of SU's up many times), e.g., needle changes or
> whether solid or valved butterflies offer any advantage, and
> (b) if you have had any experience comparing well set up HIFs with the
> DGV.
The only thing I might add to the "normal SU lore" is to emphasize the
importance of needle change with exhaust back-pressure change. I found
it IMPOSSIBLE to get my HIF4s adjusted with the ABD needles installed...
I have a straight pipe to the muffler, no resonator. This adds a real
nice bit of power in the 2.5-4.5K region but robs a bit of bottom end.
In any case, the ABDs required that I run it so rich the sparkplugs were
pitch black and building a thick layer of crud... the idle mixture was OK
but it riched as you got to cruise.
I swapped in AAE needles, with the logic that my exhaust and intake, and
pollution control, and crankcase ventilation as well, were a lot closer
to a late 60's B than a '73 B. It now works really well (dark tan plugs,
lean misfire contained to very small regions of the operating envelope...
which I think can be fixed with a change in damping fluid).
I have enough trouble with trailing-throttle enrichment with the valved
butterflies... I can't imagine soldering them shut. The valves are there
for a reason, and if the springs are in decent shape shouldn't cause any
problems.
All the hot shoes around here have swapped out their SUs for Webers.
They change the jets when they get to the race, richening the mixture. I
find in my current setup I can get the same effect (which eliminates the
slight lean stumble on rapid throttle change, and provides generally more
power, at the expense of fuel economy and idle) by pulling the choke out
about an inch. This is NOT to say that my car runs as powerfully as
theirs (far from it!) but I'm in Stock and they're in Prepared class.
Damping fluid is important. In the Spitfire's HS2s I have been running
Marvel Mystery Oil with great success. In these HIF4s, I was trying the
same thing but couldn't eliminate throttle advancement leaning (it was
BAD). I switched to plain 20W50 Castrol and it works >much< better. I
haven't tried gear lube yet <g>.
>From what I have read, a properly setup Weber has a bit more low end and
a bit less high end than a properly set up SU system. The Weber is
easier once you get a set of jets for each operating mode ("cold street",
"warm street", "cold track", "warm track", where cold and warm refer to
the weather). SUs don't let you switch between known configurations as
easily.
I set my idle to 1000 RPM or so... I think I'll be able to notch it down
to 800 after the engine work this winter (valve guides, rings, de-coke
the head, timing chain and tensioner replacement).
Hope this helps (tm). I'm just learning as I go, myself.
John M. Trindle | jtrindle@tsquare.com | Tidewater Sports Car Club
'73 MGB E Stock | '69 Spitfire E Stock | '88 RX-7 C Stock
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