> I could see that happening if a worn needle or seat created a lean running
> condition, but it seams odd that a worn needle or seat would cause a broken
> valve or overheating condition, since wearing of the parts would only cause
> the car to run richer -??
As Dave said, when improperly centered the needles wear only at the base ...
other times the taper increases the clearance and so they don't rub. (If they
are far enough off-center to rub above idle, the engine generally runs so bad
due to sticking that the problem gets solved shortly.) So, the wear causes the
idle to be very rich. (I've seen this problem so bad that the adjustment nuts
didn't have enough range to lean the idle out !). Since the mixture setting
affects the entire range, setting the correct mixture at idle with a worn needle
will cause the mixture to be lean at larger openings.
> a worn seat would run rich over the entire RPM
Keep in mind this is not a "seat" but a jet with a calibrated hole that is
"plugged up" by the needle. At idle the opening (gap between jet & needle) is
very small. For example, the first station on a SM needle is .0990" in a .100"
hole (the jet), so the opening is only .0005" (yes, that's half a thousandth) on
each side. Clearly any wear has much more of an effect on mixture at these
small openings than it does at larger ones.
> I could see poor running, bad mileage, or carbon buildup, but not engine
> damage
The engine was running extremely lean at cruise, and overheated incessantly in
warm weather. I believe the EGT was way too high, and eroded an exhaust valve
stem until it was weak enough to break. Could well have been poor quality
valves or something, but erosion was clearly present.
Randall
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