vacuum advance/ Timing

[Arthur1947]

According to past threads proper timing should be set with the vacuum advance disconnected right? I also read that setting the timing a couple degrees BTDC is the way to go. I have two Carter bb's if that makes a difference. I drove my car around the block a couple of times and noticed a hesitation, mainly between 2nd and 3rd. The idle speed sounds and feels dead-on. My Father pointed out that it might be the vacuum advance. I've already set the acc pump and that helped the stumble. I'm trying to work out the kinks so any suggestions would be appreciated.

Best.

ARTHUR

[Tom Skinner]

Dear Arthur1947,

Remember to stick a Golf Tee in the Vacumm Tube after disconecting it

then set the timing. Just diconnecting it won't do it. It must be stopped off.

Once your satisfied with the timing, hook it back up and then use a Vacumm gauge to set your Carburator Mixture Screw to the highest reading in inches.

Tom

[central52]

I didn't know that about disconnecting vacuum advance when setting the timing. Is that for a static timing, or with a timing light?

I static tuned my 47 Plymouth with it connected, and it runs fine. So, next time I do it, should I disconnect the vacuum advance? I'm confused, the service manual I have doesn't mention that procedure. Ed P.

[Don Coatney]

I personally adjust my timing with the vacuum line connected to the vacuum advance unit on the distributor. Be it right or wrong it works for me. Here is some information on the vacuum advance unit and general tune up tests. Also a good graphic explination on the difference of hot and cold spark plugs.

[greg g]

Uhhh static timing is just that static, as in no movement. The term refers to the procedure of setting a base line timing with the engine off, so the vacuum line and the presence or absence of vacuum is a moot point.

Ported vacuum from the carb at idle should be negligible, as ported timing from the carb is the opposite of manifold vacuum.

Some sources advise to advance timing a few degrees over factory specs as today's fuel has a different flame front speed than older formulations. So lighting it off a bit earlier makes up for the difference. I road timed mine to assure no spark knock under load. With the light it is at about 4 BTDC.

Some say that having two carbs reduces the ported vacuum by half, meaning vacuum advance is also halved, which also argues for a bit of initial advance above what the factory used. Also higher compression from milling heads or using aluminum heads will also call for a bit more of initial advance.

[Tom Skinner]

Dear Arthur1947,

Static Time:

Motor Off/Not Running: Ditributor Cap and Rotor Removed.

With the piston of the No.#1 Cylinder on TDC (Top Dead Center)

timing marks aligned the Points should just be opening. Loosen the Dist. Clamp

and turn housing Clockwise until Points are closed. Turn on the Ignition Switch. Hold the High Tension wire that comes out of the center of the Cap

1/4" away from a good ground. Turn the Dist. housing CounterClockwise until a Spark jumps the Gap from the High Tension Wire to Ground. At this Point The Points are just Opening. Tighten the Dist Clamp = Static Time.

Dynamic Time is Running the Engine and using a Timing Light as I described above. Once you set your timing use your Timing Light to observe if the Timing Mark advances while increasing RPM's Throttle to about 750 RPM's

If it does not you probably have Dist Advance issues, if it Advances say 5-10 Degrees then you are probably fine.

Tom

[Tom Skinner]

Dear Arthur1947,

I would like to Credit that information to "Automotive Trouble Shooting"

"For WW2 Wheeled Vehicles" Volume #1 by Robert Notman, Page #33.

I would Also Like to Credit the Dynamic Timing Description I gave you to

Poplar Mechanics Magazine May 1976 Issue Page #175.

I do it this way and it works DEAD ON. Another Service Reference Book

Prepared by Chrysler Crporation "Tech Says" Volumn #1 No.#1 Sept. 1947

describes it exactly as I have to you, using a home made Vacumm Stopper

to check for Vacumm Advance, See Imperial Web Page Tech Booklets about Distributor Advance Mechanisms. Good Luck!

Tom

[Arthur1947]

Dear Arthur1947,

I would like to Credit that information to "Automotive Trouble Shooting"

"For WW2 Wheeled Vehicles" Volume #1 by Robert Notman, Page #33.

I would Also Like to Credit the Dynamic Timing Description I gave you to

Poplar Mechanics Magazine May 1976 Issue Page #175.

I do it this way and it works DEAD ON. Another Service Reference Book

Prepared by Chrysler Crporation "Tech Says" Volumn #1 No.#1 Sept. 1947

describes it exactly as I have to you, using a home made Vacumm Stopper

to check for Vacumm Advance, See Imperial Web Page Tech Booklets about Distributor Advance Mechanisms. Good Luck!

Tom

Tom,

Thank you. I'll give it a shot.

Best.

ARTHUR

[steveplym]

Static Ignition Timing

The classic Catch-22. Your trying to get your flathead started. The engine is not running so you can't check the timing with a timing light. However you suspect the reason the engine won’t start is because the timing is set incorrectly. The solution is easy, static time the ignition.

You need a cheap neon indicator, the kind you use to check your household wall outlet. First turn the engine over by hand until the timing marks line up at top dead center (TDC). Pull the distributor cap and verify the rotor is pointing at the cylinder #1 plug tower on the distributor cap. Usually the rotor is pointing around 7:00 o’clock. If not, it means cylinder #6 is in firing position and you need to turn the engine one full revolution. One way to be sure of the firing position is to pull the front valve cover off and watch the lifters. If cylinder #1 is TDC, both valves will be closed. As you continue to turn the engine manually, the exhaust valve will open. Once TDC is set, pull the plug wire off plug #1 and hook up one lead of the neon tester to the plug connector. Connect the other neon lead to a solid ground, such as the coil bracket. I use short jumper wires with alligator clips to secure the connections.

Reinstall the distributor cap, and loosen the locking bolt on the distributor so it will rotate. Turn on the ignition. Rotate the distributor fully clockwise until you hit the stop. Then slow turn counter-clockwise until you see the neon tester flash. When the light flashes you are set for TDC. Tighten the distributor locking bolt. The advantage of starting with static timing is neither the vacuum or centrifugal advances are in use. By the way, this procedure is similar to one discussed in the Plymouth Service Manual in the Ignition System section. The service manual setup uses the ignition point circuit instead of the plug wires and a six volt bulb is used instead of a neon test light.

I used this method of timing found in the tech tips on the homepage. I used a timing light to check it after I static timed it and it was right at TDC. Car runs really well and usually the hesitation I get in the car is that I don't let it warm up enough before I run it. After it runs a few miles it smooths out just fine.

[grey beard]

I'd like to take Don Coatney's advice one step farther. On my own 1948 engine - running at warm idle - it makes no difference to engine rpm to have the vacuum advance line attached or removed - plugged or unplugged. As was pointed out earlier in this thread, the vacuum source is above the throttle plate and is negligable - not enough to make any difference at all.

Having said this, many engine manuals DO instruct you to disconnect this line before setting intital timing because some engines use manifold vacuum, which IS present at idle, and would make a differeence if left connected. The example that comes to mind is small block Chebbie V-8 engines. But never fear, you can keep this line connected to set initial timing on our flatties, and no harm will ever be caused by this practice.