Paul Wrote->>
So, my questions are-
1.) How does one diagnose a burnt exhaust valve without taking the head off.
This guys mechanic didn't, so I wondering if this is the source of the
problem.
>>>> Knock the center out of an old sparkplug, and braze/solder/epoxy a
barbed hose fitting into the body of the plug. Set the engine so the
offending Cylinder is in 'fire' @ TDC, put it in 4th and lock the E. brake
real well. (Chock the wheels A/R) install the "air plug" in the offending
chamber, and put about 30-50 psi into the chamber. ( you do have a portable
airtank or compressor??) The car may try to lurch, sometimes you'll have
to reset the cyl position...careful, here.. Run back to the exhaust pipe
outlet and listen for the presence/absence of any hissing. ( Get your ear
in real close ) If you hear nothing, try the carb intake, as an intake valve
will hiss back through the carbs... Be careful with this whole procedure,
i.e.. keep your fingers away from the fan blades, etc. As long as the cyl
is at TDC, there is little if any tendency to turn the engine. once it gets
a little way into the stroke, things will try to turn over forwards or
backwards...
2.) Having no experience with the Weber carbs, could this be the source of
the trouble? Any of you guys running these carbs have problems with the
Weber downdraft setup? Do they tend to backfire out the exhaust or through
the carb?
>>>> Webers, in general will bark a bit thru the carbs on warmup, but
should settle down when operating temp is reached. If you are seeing
exhaust backfiring, on trailing throttle, this is sometimes a sign that the
jets which control the mixture strength during the transition between the
mainjet operation and the idle jets is a bit too rich. I would strongly
suggest getting a copy of John Passini's Weber books ( 1 theory/1
operation). These carbs do take a bit of fiddlin for setup, but run really
sweet when correctly set up.
3.) Could the electronic ignition be the source? How would a sticky or non
functioning vacuum advance impact this type of ignition?
>>>>>> Get out the timing light, and check the advance with and without
the vac advance hooked up. One thing for sure: All engine systems should
be in excellent shape before trying to tune a Weber setup.. Don't even
bother looking at them until you fix the valve problem, have even
compression, no vac. leaks, and a healthy ignition system.
Good Luck
Bob Westerdale
59 3A TS36967E
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