Hi Gang,
My dad used to tell me that a car needs three things
to run; compression, spark and combustible mixture.
While he was correct, his solution was static. That is,
there was no TIME element in the solution. Let's look
at a way to address this problem.
Compression:
Verify that you have good compression on all cylinders.
If you do a compression check wet AND dry you will
get a feel for the physical condition of the engine. Plus,
you will get a test for silly things. I mean, I have seen
engines assembled WITHOUT including the pushrods!
Oversights DO happen. If you did a COMPLETE
rebuild, verify that the cam is timed correctly and that
the valve movement is correct and properly timed.
Spark:
Verify that the entire circuit is good by manually
turning the distributor to open and close the points.
You should get a hot spark. If not, dig deeper
into the ignition. I have seen condensors bad straight
from the box. I have also seen ignitions rebuilt where
the condencer was forgotton! Similarily, I have seen
ignitions rebuilt where the rotor was forgotten. Great
spark at the coil but NOTHING at the plugs.
If you DO get a hot spark, look into spark timing.
Is the spark happening at the right time? It's easy to
get the spark to fire at the correct time with respect to
TDC. Unfortunately, it is also easy to get the spark
to fire near TDC but 180 degrees wrong -- at the
end of the exhaust stroke.
Are the spark plugs new and/or gapped correctly?
This is an area where physics is at mixed purposes.
You need a larger gap to make a spark hot enough to
heat the mixture and ignite it but you also need a gap
small enough to allow the mixture to ionize. Typically
those values range from 0.040" down to 0.024" or so.
Verify the point gap or better yet, measure the dwell.
You can do this on the stater motor without the engine
running.
Fuel:
Verify that the fuel pump is filling the carburator bowl.
Most carbs expect 3 psi or so. It is a common error
to substitute a new fuel pump from a FI design. The
pressures are WAY too high and will overpower the
float valve and flood the carb bowl. It doesn't sound
like this is your problem but DO verify that you are
putting the right amount of fuel at the right pressure
at the carb. Also, make sure that it IS fuel that is
being delivered. It is not uncommon to get water
into the tank during a long restoration, if the car sat
outside the shop.
If you are using constant depression carbs (like SU
or Stromberg), the fuel-air mixture is set by lifting
a tapered needle out of a fixed diameter jet. As more
air is requested, more fuel is metered. This is hard to
measure so the small blast of starting fluid is the best
approach. If you have to do this more than one or
two times, add a few drops of oil through the spark
plug holes before trying again. That simple act will
provide ring lubrication for subsequent tests.
I guess the thrust of this note is test-test-test. Any
other approach is based upon assumption and luck.
Best regards,
Rick
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