Jeff Lo writes:
>>Well, yesterday I finally got the mixture adjusting tool for the
>>Z-S CD175's in the TR-6. I already had a Colortune and Unisyn, so
>>I thought I'd see about leaning out the mixture a bit (you could
>>often smell the gas in the exhaust). I hooked up the Colortune,
>>and as I expected the flame was very yellow at idle. Here's where
>>the fun begins. I start turning the mixture control to lean it out,
>>and I keep turning, and turning, and nothing happens. 20 turns or
>>so and nothing happens. 5 or 6 the other way and I'm back to the
>>stops at full rich. I guess I must have unscrewed the control all
>>the way. So, is the fact that the mixture control doesn't seem to
>>have any effect indicative of carbs that need to be rebuilt, or is
>>it something mode insidious than that and maybe I should try the
>>pair that are in the trunk from the parts car.
I just rebuilt the CDT150 on my '78 Midget and I can give you a brief
idea of how the mixture adjusting tool works. The carburetor has a
piston or slide with a needle that fits into a seat in the body of the
carb. The mixture is adjusted by moving the needle up and down in
relation to the piston. On a motorcycle this is accomplished by moving
a clip on the needle, but on the Z-S carb its more complicated. The
slide/needle looks something like this:
__________________
| |
| __ | <------ Slide
| | | |
| | | |
| | | <--------------- tube (can't remember
| | | | the name)
| | | |
| | | |
| |--| _|
Needle holder -------->|XX|======_| <------ Set screw
--------------------
||
||
||
|| <---- Needle
||
||
||
||
V
The special tool you have fits down in the tube into an allen wrench (1/8")
slot in the needle holder. This part is threaded and by screwing in and
out it moves the needle up and down (down=leaner, up = richer). The
"normal" setting results in the needle holder being flush with the bottom
of the slide. If you screw it too far down it will actually come out!
The set screw prevents the holder from turning (there is a grove in the
holder that the point of the set screw fits into). If the set screw is too
loose, too tight or the groove is not lined up, the needle may not actually
be moving up and down. Take your slide out of the car to do the initial
adjustments, this way you can see exactly what is happening. If you can
grab the needle and pull the needle slide out of the piston, you've gone
too far and the allen screw will need to be threaded bak into the needle
holder. (sorry for my use of non-technical terms, but I can't remember
the "official" names for these parts).
Things to look for:
1) Is the needle (or the seat) badly worn?
2) Is the allen screw screwed into the needle holder?
3) Is the needle holder flush with the bottom of the piston?
A common problem is that something breaks such that the needle
rises in the holder, causing a too rich mixture.
4) Is the choke being pulled off when the car warms up? This turned
out to be the problem on my MG. The heat mass in the water choke has
a spring on it that had streched, such that the choke was not pulling
off when the car warmed up, causing the very problem you describe.
I simply rotated the heat mass to "pre-load" the spring, adjusted the
carb back to normal and everything was fine! Take the heat mass out
(if you have a water choke) and operated the choke manually. With the
choke off, it should run OK.
Good luck!
___ __ __ __ __ Alan Dahl
/ / / / / /__/ /__/ /__/ / / North American MORPHO Systems
/ / / /__/ / \ / / / /__/ 1145 Broadway Plaza
Tacoma, WA. 98402, USA
PH: 1 (206) 593-8021
FAX: 1 (206) 591-8856 We shall not cease from exploration
...amc-gw!morpho!alan And the end of all our exploring
Will be to arrive where we started
Standard disclaimer applies... And know the place for the first time.
- T.S. Eliot
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