Dan and Listers,
I have fixed a few carbs in my time and I have a couple of thoughts in my
mind that may or may not help. If I read your email correctly you have two
complaints 1) Idling, 2) low performance off idle through low end.
1) If you are having trouble idling it sounds like it is the idle circuit
that is the problem. A couple of points you made also indicate that you
might have "adjusted" the secondary butterflies using the little flat set
screw. I am unfamiliar with the configuration of an original Holley carb ,
but most Holleys require a minor amount of clearance(mostly to avoid
interference of the butterflies with the throttle plate) but it should be
barely discernible. Assuming that you have adjusted this correctly the next
step is to determine if the power valve is correct. Do this by measuring the
vacuum signal of the engine at idle. If you have any sort of a mild cam it
is likely to rob vacuum at idle and will result in very low vacuum. Stock
Holley kits come with 6.5 powervalves and this is sufficient if your engine
is generating 7 inches of Vacuum or OVER like 10 - 15 inches. If the engine
has been modified or there is a serious vacuum leak (I assume you checked
that) the engine will not generate enough vacuum to close the power valve as
it requires at least 6.5 inches to close off the main fuel supply and run on
the idle circuit. The idle circuit is unaffected by jetting and should not
affect performance as off throttle performance is a different carb circuit.
If this is the case you must drop the power valve size (As recommended by
others on the list) to some value below your vacuum reading. I don't know
what displacement your engine is but the small 289 or 260 in. engines are
very sensitive to cam timing and its effect on vacuum. Your choices will be
5.5, 4.5, 3.5, 2.5 as it will depend on what your signal is. Choose the
power valve that is one reading below your vacuum signal as measured at the
vacuum port (located at the front of the throttle plate I think) Not the
distributor port as that will only have a signal off idle to control the
engine advance at idle that vacuum source will be 0 (zero). Once you are
sure you have the correct powervalve the begin tuning. It sounds as though
you were using the idle speed screw to try and bring up the idle rather than
the mixture screws. If you screw the mixture screws in all the way it should
stall the engine, if not you are idling on the main circuit. If you are
idling on the main it explains the idle problem and also probably leads to a
higher idle warm than when cold, if not then it may be another area but I
would need to know more about your car to offer suggestions.
2) Poor performance and hard starting. If you live at a higher altitude you
may need to jet down to smaller numerically valued jets to compensate for
thinner air density. While I don't know what the jet size currently is 66
and 68s are what I think would be reasonable in primary and secondaries
respectively depending on engine displacement. Timing is another area that
can really impact performance. I don't want to insult you but be sure that
the vacuum advance on the distributor goes to "ported" (Vacuum that is only
there off of idle and at idle registers zero) vacuum and that the advance
has not moved at all. The best performance will be seen with and initial
timing of 14-16 degrees with a total timing "all in" by 3000 rpm of around
36-38 degrees based on the Ford guys I have been quizzing lately.
kinda lengthy sorry about that,
Hope it helps!
Regards,
Tim Ronak
B382000680
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