Bud:
This is a follow up to non-altitude comments you made regarding carbs.
In my continuing carb adventure as soon as I felt I had my problems solved
by adjusting the mixture, I too encountered very high idle speeds. When
cruising at 2000 RPM, if I got off the gas and pushed the clutch in the car
stayed at 2000 RPM. It was like something was stuck open. So far I have
done the following to my car:
Rebuild by mechanic changing needles (B1AF), diaphragms, etc.
Turned the idle trim screw all the way in.
Attempted to use colortune - can't get a blue flame.
Adjusted mixture to the point of getting very close to passing the
lift the air valve test
New plugs, rotor, and cap
ATF in the dashpots
Checked the vacuum by pulling hose off distributor and plugging -
RPM went to about 1300
At this point, my carbs are adjusted to about 1 to 1/2 a turn from
full rich
I am continually swapping one problem for another. I either get a rough
engine pulling away from a start, or rough running between 1500 and 2500
RPM, or fairly good running but a 2000 RPM idle. My problems seem to come
up an hour or so into a drive once things have really warmed up under the
hood. I have done nothing with the temperature compensator to this point.
Any advice.
-----Original Message-----
From: Bud_Rolofson@nps.gov [mailto:Bud_Rolofson@nps.gov]
Sent: Wednesday, August 11, 1999 5:32 PM
To: triumphs@autox.team.net
Subject: Altitude and Carbs
In my attempts to retune the 6 since I returned home I discovered that I had
a
vacuum leak on my front carb where the vacuum line connects for the vacuum
retard. The plug failed so I think THAT was the cause of my
increased(1800-2000 RPM) idle speed problem, which began my road to ruin.
Since
I didn't catch on that I had a vacuum leak I proceeded to "fix" the wrong
thing
creating another problem. If idle speed is off you of course back off the
idle
speed screws, right? Wrong, all that does is make the butterflies stick
since
it's the idle speed screw that keeps them from closing too tightly in the
mixing
chamber. So now I'd detuned it to the point where I HADN'T solved the fast
idle
and HAD created another problem (sticking butterfly).
I'm beginning to think the ZS carbs ARE marvelous in how forgiving they are
to
people like me that just can't keep their mitts off them, since I royally
messed
them up and still made it 4500+ miles. I'm now a believer in the idea that
the
constant depression principle compensates for the change in the air density
no
matter what altitude you're at. I think that if your fuel/air mixture is
correct at lower altitudes then it will still be correct at higher altitudes
and
vice versa. I think Jim Altman's experience is a good example of this as I
believe he recently installed the B2Y (which is richer than a B1AF) needle
in
his 69 TR6 because it was previously running way too lean with the standard
B1AF. Now if HE didn't have a problem with a properly tuned RICH needle
than
maybe nobody else will have a problem with a properly tuned standard needle.
However, like every other internal combustion engine you're going to lose
some
power at higher altitudes simply because you're not getting as much air AND
gas
to combust.
Leaner needles at higher altitudes ARE recommended by none other than the
guys
at Apple Hydraulics but I believe that is in order to retain the range of
adjustment, not to CHANGE the fuel/air mixture (but I could be wrong about
this
too). The standard needle is a B1AF which is what I use in my carbs. The
next
leaner (larger by 0.010) is a B1G needle and even leaner a B1CQ needle.
When I
replaced the jets a few months back I set them at a leaner depth (higher in
the
carb body..as recommended by Apple) which is the counterpart to running a
leaner
needle since the opening on the jet is higher up the needle on the fatter
part
of the needle. The jet opening is also higher above the level of fuel in
the
float chamber so it takes a little more air to pull the fuel up and into the
mixing chamber which also makes it a little leaner.
So my bottom line is the problem I encountered on the way to VTR with high
idle
speed was not fuel/air related and if I'd discovered the vacuum leak I might
have avoided doing something stupid (OK so that's debatable) like messing
with
the timing and carbs and I would have avoided starting this thread. My
biggest
mistake was having a preconceived idea that I was going to have to adjust
for
altitude (see I knew I should have started this thread 6 months ago), now
I'm
convinced that was wrong.
I'm not just saying this so I get off the hook with Fred Thomas and Dave
Massey
either. Not that I thought for a second I could come up with a "turn per
thousand feet" solution for every TR coming to Breckenridge in 2001. Hell,
it
took me thousands of miles to figure out (with the help of many fellow
listers)
my own problem (or at least one of them). Now I know better.
Bud
71TR6 CC57365
71TR6 CC65446
66TR4A CTC57806
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