[DML] mixture issue
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[DML] mixture issue

Well, today I decided to tackle what I "sensed" was a rich mixture, based on a bit too much 
black smoke coming out the exhaust. The PO said that he had adjusted the mixture using 
an air fuel ratio meter, and that the car seemed to run best when set at an AFR of 12.5 at 
idle. Does anyone have a feel for that value for our engines?

Well, I used the dwell meter method to measure the duty cycle, and it was way off - at 
about a 10 on 8 cyl setting with not much fluctuation. So, I leaned it out by turning the 
mixture screw CCW, and I had to turn it easily 1/4 th of a turn to get it where I thought it 
should be. So, now after full warmup (fans come on and then fans go off), I get a dwell 
that fluctuates from 28-38 (8 cyl setting) and 38-48 on 6 cyl setting. I runs a bit better 
than before, no pinging, and I can feel the WOT enrichment that I could not feel before. 
Also, a white piece of paper held to the tailpipe for 1 minute at idle shows not a speck of 
black. Have not tried to start it cold, though.

So, I feel that it is now set correctly. I would like to know 1) if anyone has any thoughts on 
the AFR for our cars and 2) is the 6 cyl or 8 cyl reading correct? An old Santos file I found 
said to use the 4 cyl setting. That would put my car, based on the 8 cyl setting, at a duty 
cycle that would be way too high (multiply 8 cyl setting by 2), and indicate that it is way 
too lean. In another note from Dave, he said just aim for a 10 degree fluctuation. But I 
would think the absolute value is also important.

Steve Liggett

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