Dear Readers,
Help! I have been an owner of LBCs for many years and I
used to think that I knew how they work. The LBC in question
is a 78 B with a Weber DGV, Eurospec distributor, Ansa exhaust,
and no pollution controls (it was that way when I bought it).
For a few days I thought that I heard uneven firing on acceleration,
but it was a subtle sound difference. Then last night it happened.
On deceleration down a long hill 1 mile from home I heard uneven
running and the "brum-pop-brum" that you get from unignited gasses
in the exhaust manifold. On the back road to the house I got uneven
firing and the car didn't want to decelerate as usual with throttle
lift off.
In the driveway it was clear that only 2 cylinders were firing.
Lifting the plug wires confirmed that cylinders 3 and 4 were not
contributing their share. I had a 1500 RPM rough idle with all 4.
Only 800 RPM with either 1 or 2 disconnected and NO change with
3 or 4 disconnected or cross wired 3 to 4 or 4 to 3. OK you say,
you've got a blown head gasket web between 3 and 4. But, I get
145 to 150 psi on all four with all the plugs out except the
gauge. Blocked intake manifold? I pulled the Weber and can blow
from one end to the other. No sign of blockage can be seen or felt
in the intake manifold or cylinder 3-4 intake gallery in the head.
The valves go up and down. QED no broken cam. The timing is about
20 degreed btdc at 1500 RPM or so, the dwell is 56 degrees on my
dwell meter and the spark is off scale (at least 1 in. long)
on the plastic spark HV gauge thingy that I got for Christmas.
For the pure-of-heart among you, I shoved the Weber out of the
way and stuck the SUs back on, or at least most of the way on as it
was getting cold. That test was inconclusive, but it did run rough.
I couldn't do the plug test as I had to hold the SUs in place.
I did not check the intake manifold gasket, but it is one of the
metal-backed ones and I never had one fail. I'll check tonight.
It might be that because the "colortune" showed blue-lean mix on
#3. I didn't think to check #1 or 2.
Any thoughts?
Regards
George Dodson
More humble than yesterday
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