I don't want Todd losing sleep and I definitely don't want him slowing down!
Background and observations.
I'm surprised to learn that there is a past history of burned #3 pistons.
Candidate causes.
I agree that the only two are lean condition or too much spark advance. Todd
asked some specific questions;
-Victor did you find anything that might have caused this?-
No
-Spark advance (smog or re-curved dizzy)?-
Recurved. Now here may be the culprit. I don't own a Dial-back timing light.
Without this device, there is no real way of setting for total advance. I
use the method of detonation point. I have always maintained that a properly
timed engine WILL detonate when bogged down. I reset my timing last month
after much experimentation after the timing chain job. I advance it to the
point where it detonates then retard only to the point where it will only
detonate under unusual load, like climbing a hill in fifth at 15,000 rpm.
Trying to accelerate in the wrong gear, in the wrong rpm range. It would
detonate if I botched up the clutch of a stop as well. But 52,000 rpm in
fifth gear @ 110 mph should not fall into this unusual load category. Or
maybe it does. At that speed you are fighting against the wind. I didn't
hear it ping, but at that speed, road noise wins out over most everything.
-Front vs. rear carb mixture (are both screws set about the same)?-
Yes. And I'm a believer in a rich mixture for SU's. My plugs are sooty,
hell, everything is nice and black. But I remember The O2 sensor work done
by Chris Erickson in 96 and, more recently, Keith Williams. Many findings
are that you can be rich at idle but far leaner at high pull, due to
needle/nozzle variations. Phil Erickson just brought up that variations in
dashpot spring rates may influence mixture rates at high pull. I've never
done a hot plug check. Without a O2 (snake oil?) meter, The hot check is the
only way to check mixture at rpm/throttle points.
-Did you notice any intake manifold or carb nuts looser than others? Is the
manifold flat?-
No vacuum leaks are allowed to exist on my car!
-Were all spark plugs tight (may be hard to determine since number 3
probably had aluminum sprayed on the threads)?-
Plugs were tight.
-Any other thoughts?-
Like Todd, I want to know we will learn from this. I don't want anyone to
melt a piston and I want to speed again!
Victor
70 SRL 31113136
Los Angeles
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