My 1.5 inch SUs on my 51 MGTD MkII have just been professionally
rebuilt. Before rebuild, the SUs were so worn I could not tune them
properly so I have very little good experience in doing this correctly.
Just finished balancing and working on them. I even used a hand held
tach to SEE when the rpms changed in lieu of the judgmental test of
listening to the exhaust. The jet nuts ended up close to the TOP, and I
am not sure if this correct or proper.
So I ran another test and my SUs maybe be different than most. The "TD
Restoration Manual" says that you should turn the jet nut six flats down
and then proceed downward (toward richness) until you reach the maximum
rpms. But they say "in the rare case where initial setting (6 flats
down) is too rich already, you will hear the idling speed start to drop
off." This was my case. I ran the test and my max idle is when the nuts
are almost right at the top, close to the bottom of the housing. Can
this be? Why is mine different than the generic SUs where the nut is
usually around 10 flats down from the top for max idle? I don't
understand or am I doing something wrong.
I have just gone through the tedious procedure for setting the mixture
for the umpteen time, raising the piston 1/32nd of an inch at 900 rpms.
The speed will rise to about 1000 and then settle back down to 900. If I
raise the piston further, then the car tries to stall. With this set up,
the jet nuts are as follows:
rear SU = 2 flats down from the top
front SU = 3 flats turned down from the top.
Have you ever seen any 1.5 in SUs with the nuts so close to the top? Is
there any other checks I can do to verify that I have them now set
correctly? I guess I am still concerned about the nuts being so close to
the top, in what is usually considered the "lean zone".
Stu Keen
Venice, FL
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