>I am converting my 1980 MGB from a single Z-S 175 to a pair of
>SU HS-4's. Timing spec on the car is 10 degrees btdc at 1500 rpm.
>Do I need a different setting with the dual carbs?
>Peter Schauss email: peter.schauss@cubic.com
MGB's seem to run best at low speed with the dynamic (idle, vacuum off)
timing at around 20 before. B(P)L, as did a lot of car companies in the 70's
set the timing artificially retarded for polution reasons. Alas, in your
particular case, you run into a problem. To cover for the lack of breathing
at high rpm, the late B's have copious amounts of centrifugal advance. With
the better breathing of the two carb manifold, it is too much advance to
be able to crank the low end up much, if any. Assuming the stock issue
distributor, I would start with 12-15 before @ 850, and hook the vacuum
advance directly to manifold vacuum, bypassing the "fourth gear" valve up
on the pedal box.
Then you *may* start bumping it up a few degrees at a time. However, at the
first sign of pinging, back it down 5 degrees or more. It takes serious
detination before you can *hear* the pinging.
Randy
randy@taylor.wyvern.com
Oh, just thought of one thing you may run into. Late B's, 77 onward (especially
77's) are known for having the outer ring of the harmonic balancer slipping
around the hub. This, of ourse, makes the timing marks read wrong. Thanks to
the constant drag of the belt, the rings always slip bakwards. So, if you keep
advancing the timing, and it just runs better and better, check the index of
the timing marks. I had one the other day that ran best with the static timing
around 35 degrees (off the scale). By finding true TDC with a srewdriver down
#1 plug hole, I found that the ring was off by 20 degrees.
I have never seen a late B harmonic balancer seperate fully, ala chevies, but
a slipped ring still bothers me. I always recommend replacing it.
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