Thanks to the list for all the suggestions. I was glad to get some fresh ideas.
It reminds me that I need to keep offering ideas to help others solve their TR
problems. No one yet has responded back to me that "boy that's a stupid idea"
even when it was. Someone, somewhere, might get some help from your idea or
experience, if not now then maybe later. I've searched my Triumph List archive
for ideas that I was glad to have available (such as: the brake booster can have
a vacuum leak internally so pull and plug the hose to see if it makes a
difference in vacuum).
I did get rid of the idle drop problem when the engine is simply idling, but I
didn't get rid of the idle drop problem when the engine is decelerating.
I did an extensive check for vacuum leaks. Replaced the diaphragms in my
by-pass valves because the flexible part that holds the brass valve was toast
and barely had any flex to it. Very brittle and one had a small hole in it. It
was good I replaced them even though it didn't solve the idle drop problem.
Note of caution: Don't use the "big" gasket that goes between the carb body and
the by-pass valve or you WILL end up with a humongous vacuum leak (don't ask).
You need the "small" gasket which didn't come with the little by-pass valve kit
that I got at the local LBC parts store. The small gasket does come in the
major rebuild kit however. I used my old small gasket and went back to the
local store and dug through their box of spare carb gaskets until I found the
right ones, which I'll have for later if needed.
I next replaced the float valves (needle valves). I put in Grose-Jet valves (I
love the way they use Jet as part of the name for a valve..."There's just not
enough confusion in rebuilding a carb so let's rename a few parts so no one can
speak the same lingo.") and this solved the surge of rich mixture that I was
getting that would drop the idle 100-200 RPM. After some tuning the idle sat at
a rock solid 860-890 RPM. The engine still had a sputter once in awhile and it
finally occurred to me that I should clean all the plugs, especially those (1-3)
that had been getting the rich mixture from the front carb. That stopped the
occasional sputter. Glory Be, I finally had an engine that ran steady without a
cough, sputter, or idle drop. I'd been grinding on this problem for so long I
stood there with that empty feeling you get when you've solved the problem and
but don't know what to do next because you weren't expecting it to really work,
since nothing else had. Didn't last long though....we are talking Triumphs...on
to that noisy tach cable.
The deceleration idle drop (150-200 RPM below normal idle) may be normal for the
engine as long the engine doesn't die. Without the rich mixture surge that I
was getting the deceleration idle drop doesn't seem as shaky and it bounces
right back to 860-890 RPMs. Do TRs have a deceleration idle drop as a normal
running condition? Anybody else's TR6 do this?
What I learned is idle drop (fluctuation) can be caused by 1) vacuum leaks,
and/or 2) by leaky float valves. I also learned that it doesn't do any good to
tweak and tune and replace parts if you don't clean the darn plugs before you
try your latest solution. Clean them, try your fix, if it doesn't work clean
them again and try your next fix, and so on. It also lets you "read" the plug's
color (you want light brown) after every fix, which I believe is a better
analysis tool than any expensive monitor they've developed yet.
Thanks again for all your help.
Bud 71TR6 CC57365
71TR6 CC65446
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