I have received many responses regarding my TR6 which is missing
occasionally at speed on the highway. I figured I'd give the whole
list an update, including some information from Bob Lang that may be
of interest to others. I want also to thank all respondents, which
have included Colin Brace, Adrian Jeffries, John Lye, Doug Phillips,
Marcus Tooze, Randy Wilson, and David Yip. This response is pretty
long, but has a number of questions buried within. Any and all
comments and suggestions are welcome, as long as nobody suggests
using epoxy to repair my brake lines... :-)
Bob Lang writes:
> I noticed you specified that you are using RN12YC plugs. If you are using the
> green wires, this is wrong. The green wires are resistive. You do not need
> resistive plugs with resistive wires. I know, I have done this. You need
> non-resistor plugs or non-resstor wires. I had similar symptoms to what you
> describe.
> Hopefully, you haven't had to spend too much $$$ on this problem (yet.)
Hmm. The wires in the car are not the green ones. They are
black. I also have no idea whether or not they are resistive
wires. I'll look at the writing on them tonight, and try to
figure it out. I'll also look over the POs receipts and see if
he ordered them from Moss. (He may have picked them up at a
local auto parts store instead.)
I may have made some more progress on the missing at speed
problem. Unfortunately, I haven't driven the car under the same
circumstances as were showing the problem to see if it has been
fixed. (We have had about 4 consecutive days of on/off drizzle
keeping me from driving the TR6 to work, and a forecast for about 4
more such days... :-()
Despite last weeks rain, I was closely examining the workings of the
carbs and the throttle linkage to find out what parts are missing
from the spare set that I have. (The spare set came with the car;
I've been thinking of rebuilding the spare set over the winter, as
they're really grimy, and are missing some parts.) In examining the
ones on the car, I found that the throttle linkage doesn't seem to
work properly.
It turns out that the spindle coupling between the throttle shafts
of the carbs has play in one direction. What I mean is that if one
turns the throttle spindle for the rear carb manually, the throttle
spindle for the front carb moves too, with no play. However, if one
turns the throttle spindle for the front carb, the spindle coupling
in the middle slips for about 30 degrees, and then starts to turn
the rear carb throttle spindle. When moving the throttle linkage
from the gas pedal, I get the latter behavior (slippage). Of course
at idle when the throttle spindles are resting on the idle stop
screws, none of this matters; it only affects the mixture when the
throttle is depressed.
Because of this, when the throttle pedal is depressed, the front
carb's throttle plate is further open than the rear throttle plate.
I presume this may be causing a rich mixture in the rear carb at
speed (?) which could be responsible for my engine misses?? This is
speculation, and I haven't really figured out how the mixture is
controlled in enough detail to figure this all out for sure.
Last night, I replaced the spindle coupling with the one from the
spare set of carbs. This one has no play in it whatsoever. Not
only that, but the mechanism which allows a few degrees of travel
from the throttle control rod before the throttle shaft begins to
turn is rusted stuck. (TRF, Moss, and VB do not currently list this
item.) Does anybody know if using that one with no slack permitted
with respect to the throttle control rod will cause problems?
I also removed the spark plugs again, and found that the rear ones
had significant carbon build-up again, and that the front ones had
some carbon build-up, but not as bad as the rear ones. After
cleaning and replacing the plugs, I took the car for a quick drive,
and had no problems whatsoever with missing. Then again, I didn't
try the scenario that is (was?) causing the most misses. (which is
to take the TR6 onto the highway at 60mph on a 40F morning after
only 10 minutes of driving.)
While I had the plugs out, I finally performed a compression check.
I found a variation from 110psi to 128psi. The low ones were #1
(about 114 psi) and #4 (about 110 psi). #3 / #5 were the highest
at 128psi, and #2 / #6 were at about 120psi. I am presuming that
these figures are essentially close enough to indicate proper
compression. I also tested #4 wet (after about 2 squirts of motor
oil) and found 125 psi, so I may have some ring wear there (or, I
suppose I may have not had the compression tester screwed in tightly
the first time...)
--ken
Kenneth B. Streeter | ARPA: streeter@sanders.com
Lockheed Sanders | UUCP: ...!uunet!sanders.com!streeter
PTP2-A001 |
65 River Road | Voice: (603) 885-9604
Hudson, NH 03051 | Fax: (603) 885-0631
|