Peter---I believe the centrifugal advance should give 20 deg. of
advance, when 'all in'. (Approximately 3500 rpm) If you are seeing 20
deg. at 2500 with centrifugal only, you should get more advance with the
vacuum advance in operation, engine unloaded. That was the purpose of
these units, as you know. It woud be good to use a vacuum gauge on the
lines that you are using at both advance and retard pots. That would
take all of the guess work out of what the distributor is responding to.
There are tappings at the carb that only see vacuum with the throttle
plate shut (what you want for retard) and others have vacuum with the
throttle plate open (what you want for the advance) If the "machine
shop added a fitting" on the engine side of the carb flange, you will
have vacuum only when the throttle is closed. Again, check this with a
vacuum gauge, or a "Baggie", if you just need to know it's present.
The 4 deg. glitch every 3-4 seconds at the timing marker doesen't
correspond to any cycle of the engine that I can think of. Many of these
distributors have some jumping around, either from play in thedist.
shaft bushings of even a bent shaft up near the rotor.
To get you distributor body positioned to take away the poor tach drive
cable angle, this can be done easy enough. Jog the engine over to where
#1 piston is firing, for a reference point. Note where the rotor is.
Take out two bolts for the dist. pedestal, to expose the drive gear.
Lift it out, first noting the slot angle where the bottom of the dist.
engages. With a screwdriver, turn the oil pump slot counterclockwise
approx. 15deg. This is how much you will want to move the drive gear
when you drop it back into the pedestal. This about one tooth. Your
timing will not change, only the position of the dist. and of course the
tach drive.
The new cable position will almost go over the 'corner' of the fuel pump
lid.
Holler, if some of the above needs further 'splainin'.
Dick
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