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Getting the right springs for the V8 carburettors
and throttle cable
Richard Withington sought help on the V8BB with a carburettor
problem. Bob Owen responds. (Jun 11)
Richard Withington
sought help saying I have looked through the workshop notes
but so far failed to find anything which would give me guidance
on the throttle return springs on the carburettors of the MGBGTV8.
The throttles are failing to return to the slow running speed
and I think there are two springs missing, which I have ordered
from SC Parts (1980 in their catalogue) but I am not sure quite
how they fit. My V8 is a Factory MGBGTV8 with rubber bumpers
and I understand the return spring arrangement is different
to the chrome bumper cars.
Bob Owen responded with a photo of the carburettor set
up on his 1974 chrome bumper V8 showing three return springs,
a torque spring on each carburettor throttle spindle and a coil
spring on the cable itself.
Richard Withington clarified his V8 has the three springs
as indicated in the photo alongside saying "but the throttles
do not return to the slow running position which has made me
question whether something is missing. I can manually press
the spindles back with light finger pressure which just makes
me think extra spring pressure would solve the problem".
Bob Owen noted the throttle spindles should turn freely.
The flexi-coupling between the two carburettors should allow
some misalignment without any resulting binding. The torque
springs on each carburettor should return the spindle sharply
to the stop if you rotate it. The throttle spring in effect
returns just the throttle cable - I assume you've checked the
cable for smoothness and that the accelerator pedal pivots freely
in its mounting.
Jim Gibson, with a rubber bumper V8, said there is no
difference, so far as I can see or find in the manual, between
CB and RB. I can't think of any reason that there would be.
If you try to pull on the coupling between the carburettors
(or on the throttle control cable near the carburettors) you
should certainly feel the resistance of the throttle return
springs even without the cable return spring. Looking at my
V8 the spring has 11 full turns and about 1/8 turn, from the
long leg that goes towards the rear and under the screw head,
to the shorter leg that hooks around the "anchor".
Maybe yours has been replaced without being wound up enough?
I suspect one turn difference will give enough torque change
from 'not enough' to 'plenty'.
Incidentally,
the parts catalogue (the real one, part number AKM0039 ) lists
different parts numbers for those springs for each carburettor
-for the LH |
carburettor
is AUD4272 and for the RH is AUD4273. The springs must be different
because they are mirror images of each other. Item 10 in the
SC catalogue no 5468 appears to be the correct throttle cable
return spring - BL part number BHH1781 (which isn't actually
listed in the BL parts catalogue but the B&G catalogue has
that number). Only one is needed.
Richard Withington replied that after some deliberation,
not to mention skinned knuckles, the conclusion after looking
at Bob's photograph, it seemed that the throttle cable return
spring on his car was a weaker version. At some time, someone
had fitted a much inferior spring which, over time had lost
much resistance and although it appeared to pull the cable back
it was failing to pull the spindles fully. I counted the turns
on the torque springs, and these seem to be fine. Anyway as
always it seems obvious after the event - the solution was quite
simple.
See
MGB & V8 Parts Catalogue AKM0039 page 108 D61-63, V8 Workshop
Manual Supplement AKD8468 page 19.15.02 and SU leaflet AKD7521
(copy available on the V8 website).
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