Dear Tom
and Ray:
I am hoping
you can help with a problem I am
having with my wife's 1967 Camaro
Convertible. She drove it daily to
work until about a year ago, when
this problem developed. Four
different mechanics can't find the
problem. It burns up a set of spark
plugs in less than a week. All of
the burned plugs are black with soot
and they all look the same. The
motor, which was completely rebuilt
six years ago, is a 327 V-8. Two
different people have rebuilt the
carburetor, and then we bought two
different rebuilt carburetors. I
also had the valve seals changed,
even though the car doesn't use oil.
Two of the mechanics tried hotter
plugs. I had a new coil and
distributor put on. The compression
is good. Any advice or direction
would be greatly appreciated.
Richard
Tom:
I'll bet you want some advice or
direction, Richard. Especially now
that you've spend a thousand bucks
and 23 weekends trying to fix this
thing.
Ray:
I think you have an obscure problem
called "manifold burn through."
Tom:
I had that once after eating at my
mother's house. I was chewing
antacids for about a month after
that.
Ray:
In this particular engine, some of
the hot exhaust is sent through a
passage in the intake manifold. Why
do they send hot exhaust through the
manifold? Because it runs directly
underneath the carburetor, and heats
it up, which makes the car warm up
faster and run more efficiently.
Tom:
But when the engine gets old enough,
that hot exhaust can burn a hole
right through the manifold. All it
takes is a pin hole. And then that
hot exhaust gets sucked into the
carburetor where it contaminates the
fresh mixture.
Ray:
And if exhaust is getting sucked
into the carburetor instead of fresh
air, the engine will suffer from
oxygen starvation, and will behave
as if the mixture is way too rich
(too much gas, not enough air). And
what's the sign of a too-rich
mixture? Black spark plugs! So
remove the intake manifold and check
for a pin hole under the carburetor.
It think you'll find one.
Tom:
Brilliant! Brilliant, Raymond. What
a brilliant deduction!
Ray:
Well, it'll be brilliant if it's
right. If not, what's another eight
or ten weekends in the driveway,
right Richard?
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