Hey! All you combustion chemistry wizards!

I've been gradually twisting the K-jet "CO adjustment" screw counter-clockwise to lean out the engine and test the effects on performance, economy and am now wondering about detonation. I read that it might not have audible symptoms. The timing is set back to about stock 12 BTDC opening to 22-24 on advance.

What is a certain indicator that mix is too lean? I've seen references to aircraft engines where they lean out the engine until just one (the weakest) cylinder misfires, and then back off slightly.

I have not heard pinging at all at this timing setting, at any mix setting. I notice the idle to get a little skip in it as I lean it down, but I hear no pinging under WOT acceleration. I don't really care about acceleration performance; seems my commute is usually in the company of semis in traffic, who mosey away from lights. I want best fuel economy and long engine life.

I've noticed a slight decrease in accceleration performance at the last 45 (1/8th turn) degree twist, and the idle got a little skip in it, but it is still far smoother than the previously overrich setting. Am I doing mechanical damage?

The temp stays constant, although it did move to the bottom of the "N" when I initially leaned it out, and it creeped just a little in hot stalled traffic.

I have read about the difference between pre-ignition and detonation, but still don't know how to determine if it's detonating.

Does anyone have exhaust gas analysis or anything to indicate best mix for these engines? Did Volvo do it by balancing the feel, sound, smell, economy, longevity?





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'74 145e T-5 'Orange Alert'