[zeebo]

got a new snap on timing light and was giving my lemans a small tune up today--points, plugs..carb adjust..and i put the beam on the timing tab--i have 13 degrees initial, and with the dial back light, i have 19 degrees added when the vacuum advance is plugged back in...i think that that may be too much advance at idle? the motor is a stock 73 400 that is tired, but runs ok..just was asking for opinions on what i should do. thanks!

[54nomore]

I don't know the distributor specs for 1973, but somewhere around 20 degrees from the vacuum advance is pretty typical. If it were hooked to ported vacuum, the engine might not like having only the 13 degrees at idle.?
I think it's probably fine where it is on a low compression stocker.

Ron.

[ta man]

Sounds about right...try moving your initial advance up a few degrees..it should perk the old girl up.

[zeebo]

yeah, 54, when i unplug the vacuum advance and cap the line, it doesnt really run too good at 13btdc..plug it back in and it smooths right out..my idle in park is 850, and it drops to about 650 in drive. yeah shes a good running motor, but tired..hi po heads and cam in the years to come....carb is been redone by cliff and i have adjusted the idle mix screws to what i believe is pretty good idle speed and im pulling about 18" of vacuum with manifold vacuum to the advance.

[dmac]

Try using a ported source for vacuum. Set the timing to maybe 15*` and adjust carb to pull good vacuum and idle good(in gear if auto transmission). See how it runs at a steady cruise speed just rolling down the highway with vacuum on a ported source.
Then try it with the advance hooked up to manifold vacuum. again readjusting idle screws for best vacuum, take another steady cruise, and stick with whichever makes you happy.

[paul s.]

Zeebo, what that is telling you is you need more initial timing. It should run smoothly without the vacuum advance. Yes, adding manifold vacuum advance at idle will pick up the rpm even more, and allow less idle speed screw, ensuring you can run off the mixture needles as opposed to using the transfer slot, but you don't want to rely too heavily on it. If you have a Saturday where you feel like tinkering; up your timing a few degrees like was advised by ta man and see how she does. Depending on your total timing (initial + mechanical) you may not need to "mechanically" recurve the distributor. On a low compression engine, as much as 40 degrees is not out of the question. On a high compression engine (9.5+) with moderate cam timing, I like to start out at 32-34 to be safe and go from there.

As for the vacuum advance, I would limit it to about 10-12 degrees. On low compression engines, I like manifold vacuum. I am not familiar with oem vacuum canister part numbers, perhaps someone can chime in there if they know of one that gives the most advance at the lowest vacuum, but I like going with an aftermarket adjustable piece and set it up to initiate movement at the lowest vacuum, and then I limit the stroke of the rod. That has always worked well for me.

Should be a piece of cake for you. Good luck with your project!