Mike,
I'm sorry I'm late chiming in on this (still on summer digest mode) and I
don't know if you solved this yet but...
I really beat my head into the wall over this same problem when I rebuilt my
carbs last winter. I went bonkers checking for leaks...I tried REALLY strong
return springs and it didn't do any good.
As it turned out, the pressed steel arms on the throttle shaft, especially
the ones that connect to the return springs and the linkage, were a little
loose. These pressed steel arms have a semi-rectangular hole that engages
flats on the throttle shaft. This hole wears to an odd "bow-tie" shape over
time, and it only takes a teeny, tiny bit of play here to cause erratic
idle - erratic idle return.
The cure was to "stake" the holes arms with a punch. I placed the arm flat
on an anvil, and tapped with a punch around the semi rectangular hole. This
made the hole a little smaller for a much tighter fit on the throttle shaft.
It didn't absolutely and totally cure the problem, but it went from from
"totally unacceptable" to "I can live with that." It's actually gotten even
better over time.
I also couldn't overstress the need to have a smooth, well lubricated
linkage. Over-tightening the carbs with bind the throttle shafts, too...
I suppose new arms would be the cure for a really worn set. I like my low $$
approach too. This cure should apply to ANY Triumph with the pressed steel
arms. HS2's, HS4's, HS6's, and (I think) all Stromberg carbs....
Good Luck,
Chris Lillja
'66 TR4A
'74 Norton Commando 850
'71 Spit MKIV
http://members.aol.com/lilljaweb/index.html
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