The Murphy Builders Site

Merry Christmas everyone.

I have a couple of mysteries that I thought I'd plop on the list and see if
anyone has any ideas.

1. Mixture control: I have a mixture control plate that goes between the
metering plate and the float bowl on the primary side of a Holley 650 double
pumper. There is a shaft with two slots cut halfway through the shaft that
line up where the jets would be in the metering plate. Rotate the shaft and
more or less of the slot is exposed giving me mixture control. I tested
this setup on my 1968 Mustang. At 60 mph I slowly leaned the mixture and it
acted just like you would expect in an airplane. The rpm would rise and the
engine would smooth out until a certain point and then the engine would
start to run rough until I richened the mixture a bit. I figured I was
finding peak lean and then coming back to a bit rich of peak in this manner.
However, when I tried this on the Chevy on the SR the rpm would continuously
rise without any roughness right up until I hit idle cutoff. This was
starting at about 1700 rpm and ending at about 2100 rpm. I was able to find
a point where it seemed like the engine was the smoothest before reaching
idle cutoff but it was very subtle. The engine ran pretty good all the way
to idle cutoff.

2. I have oil leaks. I have Airflow Research heads and they have 8
headbolts each that are outside of the valve covers below the exhaust ports.
That seems to be the source of my oil leaks. It looks like oil is migrating
out around those bolts. There is no sign of coolant either outside of the
engine or in the engine oil. (I drained the oil after my first runs.) I
checked the headbolt torque and they were fine. Oil has continued to leak
since the last time I ran the engine on November 5th, even after I drained
the oil. I know a teaspoon of oil can look like a cup when it pools on the
ground but I can't believe that I have been cleaning up a pool of oil on top
of my radiator scoop regularly since the last engine run. The Airflow
Research head installation instructions only mention using a sealant on
bolts that enter into the block water jacketing. There are no bolts in the
water jacketing in my block. I did not use any sealant on my bolts. I did
use anti-seize as specified by the instructions. The engine was exposed to
overly high temps for a total of less than 10 minutes in separate short runs
before I figured out that the timing was too retarded. Perhaps I damaged
the head gaskets on both sides in such a way that only oil is getting past,
no coolant?

Any ideas would be greatly appreciated.

Mike




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Hi Mike

Gotta think about your mixture situation a bit as I think I've heard a
similar story before. Was the prop installed?

I don't know your engine but whenever I've seen a head bolt associated
oil leak it has indeed been out through the head gasket. Any chance the
gasket is not the right one or was not oriented correctly such that the
re-inforcing is not around the oil gallery? If the quantity is really
that much after shutdown though it sounds more like oil pooled under the
rocker cover is leaking out of the rocker cover?? When I get frustrated
by oil leaks that I can't pinpoint, I throw in some fluorescent dye and
get out the ultra violet light.

Ken

Mike Kimball wrote:

Merry Christmas everyone.

I have a couple of mysteries that I thought I'd plop on the list and see if
anyone has any ideas.

1. Mixture control: I have a mixture control plate that goes between the
metering plate and the float bowl on the primary side of a Holley 650 double
pumper. There is a shaft with two slots cut halfway through the shaft that
line up where the jets would be in the metering plate. Rotate the shaft and
more or less of the slot is exposed giving me mixture control. I tested
this setup on my 1968 Mustang. At 60 mph I slowly leaned the mixture and it
acted just like you would expect in an airplane. The rpm would rise and the
engine would smooth out until a certain point and then the engine would
start to run rough until I richened the mixture a bit. I figured I was
finding peak lean and then coming back to a bit rich of peak in this manner.
However, when I tried this on the Chevy on the SR the rpm would continuously
rise without any roughness right up until I hit idle cutoff. This was
starting at about 1700 rpm and ending at about 2100 rpm. I was able to find
a point where it seemed like the engine was the smoothest before reaching
idle cutoff but it was very subtle. The engine ran pretty good all the way
to idle cutoff.

2. I have oil leaks. I have Airflow Research heads and they have 8
headbolts each that are outside of the valve covers below the exhaust ports.
That seems to be the source of my oil leaks. It looks like oil is migrating
out around those bolts. There is no sign of coolant either outside of the
engine or in the engine oil. (I drained the oil after my first runs.) I
checked the headbolt torque and they were fine. Oil has continued to leak
since the last time I ran the engine on November 5th, even after I drained
the oil. I know a teaspoon of oil can look like a cup when it pools on the
ground but I can't believe that I have been cleaning up a pool of oil on top
of my radiator scoop regularly since the last engine run. The Airflow
Research head installation instructions only mention using a sealant on
bolts that enter into the block water jacketing. There are no bolts in the
water jacketing in my block. I did not use any sealant on my bolts. I did
use anti-seize as specified by the instructions. The engine was exposed to
overly high temps for a total of less than 10 minutes in separate short runs
before I figured out that the timing was too retarded. Perhaps I damaged
the head gaskets on both sides in such a way that only oil is getting past,
no coolant?

Any ideas would be greatly appreciated.

Mike

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