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My SU carbs suck

Subject: My SU carbs suck
From: "Jerry Causey" <>
Date: Sat, 30 Dec 1995 19:18:07 -0800
My dear spouse gave me a Gunson's Colortune for Christmas, which I 
put to immediate use on my '67 MGB. Part of my 12 step program to More 
Power (with the least cash outlay),  was to purchase an intake manifold 
from Seven Enterprises, and a pair of ex-Volvo SU HS-6 carburettors 
from a local (when I lived in Southern California) junk yard. I had 
them rebushed, fitted blue springs, and after a bit of trial and 
error, SY needles. I am using Moss genuine SU dashpot oil, and I also 
have a centrifugal-only distributor. With my new Colortune, I set the 
idle to just-barely-yellow on the #1 and #4 cylinders. Now my idle is 
fairly smooth (about 850 RPM), acceleration is just fine, and 
steady-state running is also just fine. However, when I drive to town at 
an almost legal 60mph, then back off the throttle to make the 90 
degree turn off the highway, strange things happen. First, when I blip the 
throttle as I downshift, doing all that fancy heel-toe stuff (I have a large 
size accelerator pedal from a later MGB), the engine kind of gags, then, 
after I make the turn, I continue on over-run in second gear about one block 
to the stop sign. If I just put in the clutch and shift into neutral 
at the stop sign, the engine dies. If I try to blip the throttle, it acts like 
normal carb with a bad accelerator pump. If I just floor the throttle and hold 
it, the engine comes back to life.

Questions:  The temperature is in the 40s F here during the day, high 
20s at night, is my dashpot oil too thick, holding the pistons up for too 
long? Would changing to that magic ATF stuff help? Should I try heavier 
springs, and if so, what color?

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