I will warn you now, this is pretty long-winded, but if you have a gas
tester or are thinking about buying one, you may want to take five
minutes and read it.
I got a Gunson's Gas Tester for Christmas and of course, had to go out
to the garage and use it as soon as possible.
I knew I was getting it so in preparation, I ordered a new needle (45H)
for my "excellent" Z/S carb. I had trouble passing emissions here in NJ
with the current needle that I suspected of too much wear.
I got the car to pass by taking the needle out and adding a ball bearing
on top of the needle to make it push out more.
This pushed the needle out so far that you could read "45H" when it was
in the damper piston!
After I reinstalled the needle and then the damper assembly, the car was
really lean so I followed the enrichening procedure to enrichen it as
much as possible, which got the car to idle enough to pass with flying
colors. The recommended CO% at idle is 5 1/2%, my reading for the test
was around 3-3 1/2%!
This is definitely not good to run the motor at that lean a setting, it
would backfire through the carb every time I goosed the accelerator, so
I pulled the ballbearing out when I got home and then leaned it as far
as it would go.
So back to my Gas tester, I left the original needle in the carb and ran
an initial test on that which without any adjustment gave me a reading
of 12.5%!!!!
so then I started adjusting the airbleed valves to get the CO down, and
it would only go as far as 10.5% at best.
There is no way of adjusting the needle to enrichen it without the ball
bearing inserted and that is sort of hokie and not in the original
design, hence a new needle.
So I put the new needle in and reset my air bleed valve at the middle of
its travel according to the manual, then I resume testing.
My initial reading with the new needle was between 8 1/2% - 9%!!
Then I began playing with the airbleed valve and could only get it to
between 7 1/2% - 8%.
When I leaned the needle with the shop tool (correct method - no ball
bearings) I could only get it down to 6 1/2% - 7%!
Prior to every time I would try to lean the needle more, I would return
the airbleed to the middle of its adjustment range so as to have a full
range of adjustment.
Consequently, I took a measurement with vernier calipers on the thickest
part of the old and new needles and found the old needle to be .001"
worn down.
In the end, I took a piece of copper wire and placed it on top of the
needle where the needle meets the retaining clip in the sleeve.
This did what the ball bearing essentially did, but to a lower degree.
When I reinstalled it this time, I got a CO reading of 2 1/2 - 3%!!
Way too lean!
So I enrichened it by 3/4 of a turn and brought the CO% back up to 5
1/2%.
I thought that that was great and that the car was now actually tuned,
nice idea, but it gets better.
Before you start testing, you have to get the tester to calibrate and
settle at a reading of 2.0% in ambient air. Then you perform your tests,
then you have to let the Gas tester reacclimate itself before turning it
off, so you have to let it stand in clean open air for 10-15 minutes so
it recalibrates and purges itself for next time.
But also from this purge period, you can learn if the tester was out of
calibrartion at all.
Well, if the tester registers lower after standing, you subtract that
underamount from the last reading ie; my last reading was 5 1/2%, but
the tester purged down to a calibration (post-test) of 1.2%.
The tester should be calibrated to 2.0% so I subtract the difference
(.8%) from the last reading and get a real reading of 4.7%.
That is still too lean and explains why the car is still backfiring
through the carb!!
If anyone else has one of these and has tips, I would love to hear from
you!
TIA,
Erik.
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