Hello Listers, Dick, Michael,
Last week I posted a question about my carb tuning, here's an update for
those that are interested.
My car, a '74 TR6 with a '73 head has a kent TH5 cam, 9.5 compression and
all emission equipment removed. I was experiencing some misfiring when
accelerating from idle, especially with a hot engine, in the 1000 - 3000 rpm
band.
After carb tuning I was led to believe that there may be some ingnition
problem causing the misses. So I rechecked the electrical components
(swapped the bobine) and replaced the usual tune up parts. Result is that I
still have the same problem and have ruled out an electrical failure. This
at least is in line with the fact that the car runs good both at idle and
above 3000 rpm.
Although I believed the carbs to be tuned fairly well there are two issues:
I had a 'APK' last week, this is the Dutch annual tech and smog test and I
had to set the carbs lean at idle in order to pass the test (but I passed!).
This made the engine run erratic, but learned me that the setting of the
carbs is pretty rich at idle. The plugs however look the right kind of
brown. I set the carbs back to the setting before 'APK' because that makes
the car run better.
Thinking that the misses can be caused by a lean mixture under acceleration
and with in mind that the hotter the car, the more misses I get, I decided
to put a heavier oil in the dampers. The damper oil gets hot in the end,
causing the piston to lift faster. I changed to 20/50 engine oil, I used
10/30 before that. This made the car's behaviour better but still giving
misses after a longer drive. Before changing the oil I tried a choke test
Dick Taylor suggested, pulling the choke a little under acceleration to
richen the mixture but that does nothing. This BTW may be caused by choke
valves full of goo. I did not take them off yet (hey, the car starts easy
enough!) but will do so anyway.
I am back at the carbs as beiing the problem to solve. I have a rebuild
planned for next winter but want to be driving the next months. Also a
reputable carb rebuilder in our country one time suggested that with my
engine mod's I don't need the (locally) popular change to SU carbs to free
all available horses but could do with other needles in the ZS's. He
suggested B1AW needles. I have not been able to get in touch with this
person but I think this is the path I will explore next.
Anyone out there that has experience with other than standard (B1AF) needles
in ZS carbs?
Regards,
Marc
'74 TR6, The Netherlands
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