This weekend, I offered to help a friend (Pete) tune the carbs on
his 74 TR6. It's not in great shape but it's sound: he uses it
as his daily driver. It has dual Z-S 175's with manual choke.
Not long ago, he complained about the car running rough. I
suggested he take the tops off the carbs and check the
diaphragms. He informed me both were torn and the car ran
"massively" better after he replaced them. (He left everything
else on the carbs alone.)
This weekend I suggested tuning the carbs so his 6 would run even
better. I brought my "S353" mixture adjustment tool, Colortune,
and an airflow meter and figured we ought to be able to get
things all synchronized and tuned up in no time (I've never had
trouble getting my 75 TR7 tuned up and it has roughly the same
carb setup). Well, it wasn't that easy.
Here's the problem:
(1) We could NOT get the airflow balanced at idle. The carbs
WERE pretty closely balanced at about 1600 RPM. However, at idle
the front carb always flowed about twice the air the rear did.
By tweaking the idle stop screw on the rear carb quite a bit, we
could get the two airflows close, but then the idle speed was
about 1800 RPM too. Not right. (Yes, we were clear of the fast
idle cams and the chokes were fully home).
(2) I thought perhaps the mixtures might not be matched.
However, both carbs showed the same mixture (color) on Colortune:
a nice blue tinged with only a bit of yellow.
(3) I double checked the diaphragms. They were both installed
correctly.
Any suggestions? Here's some questions I had last night:
(1) Perhaps one of the deceleration valves was floating off
seat?
(2) Perhaps one of the carbs has an air leak? Could that affect
the idle flow rates? How do you find such a leak?
(3) Maybe the throttle plate on the front carb has worn so that
it "leaks" more air through than the rear at idle?
I'd welcome any suggestions. You can write to me personally at
the address below, or, if you think it networthy, post it.
Many thanks!
Pete and
jim
jatc@emx.utexas.edu
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