Well, now that the TR6 is street-worthy, in that it passes the NH
state inspection, and runs pretty well, I'm getting a little more
picky about what is wrong with it...
The current problem is one that I hadn't noticed until doing highway
driving with the car to and from work. The problem never gets a
chance to exhibit itself on smaller roads.
What happens is that the TR6 will occasionally "miss" two or three
times at speed on the highway (around 2700-3000RPM in 4th). This
typically happens about 1 minute after running at speed, will happen
just a few times, and will then typically be gone for the rest of the
time on the highway. When I get on the highway, the engine is warmed
up (although probably not completely) as I've been driving about 7
miles in 10 minutes over small roads.
On a couple occasions, I have gotten occasional misses after the first
couple minutes on the highway, as well.
I've also been keeping track of my gas mileage -- it seems pretty
poor. I'm getting only about 17 mpg; I had been expecting over 20 for
a TR6. Then again, I can't be quite sure about this, since my
odometer doesn't work. (I'm guessing at the mileage between gas
changes, by adding up the miles of the trips I've driven in the car.)
So, you may ask, what have I done so far to find out what is wrong?
Last night, I took out the spark plugs. They are Champion RN9YC
plugs. My car is a '74, and I've seen conflicting information for the
correct plug type. The Bentley workshop manual indicates RN12YC for
'69-'72, and RN9YC for '73-'76. However, the TRF specs indicate the
reverse -- RN9YC for early cars, and RN12YC for later cars. The
Champion spec guide at the auto store agrees with TRF. I presume that
since the RN12YC is the hotter plug, that it would go in the lower
compression engine, thus the later car. Does this mean the Bentley
workshop manual is wrong? I am not sure that the engine is the
original one for the car. The commision number is CF27535, the engine
number is CF13XXX (I can't remember the whole thing.) I know that
numbers didn't usually match from the factory, but being off by 14K
seems a little excessive. In any case, the CF13XXX engine is still
from a '74, but who knows if it has been modified some time ages
ago... As another data point, I have been running 89 octane gas in
the car, with no indication of pinging, so I would doubt the engine
has been modified for high compression.
Since I figured it couldn't hurt to try, I swapped the old RN9YC plugs
for new RN12YC ones. As to the condition of the old plugs: they all
looked like they were in decent shape. However, the rear three plugs,
particularly #4 and #5, all had carbon buildup on them; the front ones
looked mostly as expected, but did have some carbon on the plug base.
Would this indicate that I'm simply running rich in the rear carb?
Could this be the cause of my highway misses?
The engine idles pretty smoothly, and runs well on country roads, it's
just missing after a minute or so at a steady high RPM in 4th. I've
tried running the car for a minute at 3000RPM in 3rd, but the problem
doesn't occur. Presumably, there isn't enough load on the engine at
3000RPM in third to cause it to miss? The only other time the engine
misses is when under load when the engine is cold -- There's a good
hill to climb just 200 yards from my house. If I don't let the car
warm up for 2 or 3 minutes before leaving the driveway, the engine
will miss a couple times climbing up the hill if I choose a gear which
will require over 2500RPM when climbing the hill. (If I ascend the
hill slowly in 3rd, at about 2000RPM, the engine runs smoothly.)
So, my question is, what to do now? I presume I need to lean the
mixture on the rear carb, but have never adjusted the carbs before,
and am a little concerned I may not help things much. Am I going to
need special tools to be able to tune the car any better than it
already is?
--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
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