Jerry and all,
If your distributor has the smog advance (original equipment on '68 thru
'70 and stamped 17.5 on the plate under the breaker plate), you should
replace it with a non smog (stamped 7.5). In the mean time, with a 17.5
you should set the idle timing at 0 degrees TDC. If you have the 7.5,
set the timing at 16 degrees BTDC (20 for Solex). If you need to know
how to determine which you have, read below. I have a bag full of 7.5
plates if you want one (N/C), along with instructions on how to install
it with non-smog springs.
You can determine whether your distributor is smog or non-smog curved by
one of 2 ways described below. The smog is a 17.5, which produces 35
degrees of advance, which is bad. The non-smog is 7.5, which produces
15 degrees of advance, which is what you want.
1. Use a timing light and see how much the timing advances as you
increase the engine
speed from idle (700 - 800 rpm) up to 4000 rpm. The span between the 5
timing marks
on the pulley represents 20 degrees, from one end of the marks to the
other end. So each
small mark represents 5 degrees. You will use this span as a reference
to judge how much
your timing advances as you increase the engine speed from idle to 4000
rpm. If it is
smog curved, you will see 35 degrees of advance (and the timing is
supposed to be set at
0 TDC at idle). If it is non-smog curved, you will see only 15 degrees
of advance from
idle to 4000 rpm (the idle timing should be set at about 16 degrees
BTDC). So if the
timing is set correctly, with either advance curve you will see the
timing light flash beyond
the last timing mark at 4000 rpm, assuming the advance mechanism is
working properly.
OR
2. You can look at the distributor cam. This requires removing the
distributor cap and the 2 screws on the outside that hold the vacuum
controller to the distributor housing. Pull out the vacuum controller
(this may require that you gently pry the lever up and off the pin on
the breaker plate). Remove the 2 screws holding the breaker plate to
the distributor housing (the same 2 screws that hold the 2 clips for the
cap on some distributors). Remove the breaker plate. There is no need
to remove the points; the timing and points gap won't be disturbed this
way. Deep inside you'll see a plate on the bottom of the rotor shaft.
If you can read the number 7.5, it is a non-smog advance curve (good).
If it is 17.5, it is smog (bad). If you can't read the # because of
grease or whatever, the 7.5 plate has radial slots, while the 17.5 has
diagonal slots. Clean it up and lube it while you have it exposed.
I've seen lots of stuck mechanisms and loose/broken springs. Make sure
it moves freely (except for spring tension) and snaps back to the point
where the pegs on the weights retract completely to the inside end of
the slots on the cam.
Gary Boone
'70 2000
http://www.wycroc.org/
http://www.picturetrail.com/gallery/view?p=999&gid=271132&uid=146317
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