Timing and vacuum

[Thunderduckie]

Timing has been set with a NuRex timing wrench (not sure if I trust it yet), points are gaped at .025 and the cap is gaped to .020. Motor is currently running between 190 and 200 even while driving. We put a vacuum gauge on the truck today and only made 16 pounds with the spark advance all the way up. When we pulled the spark advance all the way down we made 19 pounds. Everything I have read says that 16 pounds of vacuum indicates that the timing is to far advanced and this will cause an overheat.
Just so everyone knows, I have use the method posted on YouTube by Jack Baum to time our cars because it always works VERY well. But, Dad saw this wrench and he SWEARS its so much more accurate.
I cannot find anything concrete online to tell me what kind of vacuum a Model A should make so I was hoping that you guys could point me in the right direction. Also, are these wrenches really that great or am I just to set in my ways of the old school mechanic (lol.....I'm 39)

One more thing I was wondering about. Dad said that he read that the spark advance is supposed to be about 3/4 down for daily driving but I thought that it was supposed to be about 1/4 down until you pulled a hill and then advanced it as needed. Can someone please tell me which is correct?

Thanks in advance for any help guys. Attached are a few pictures of our cars. Both have been completely restored by us. Dad and I have been bitten really hard by the "A Bug" as we call it and we want to make sure that we don't mistakenly destroy a part of history.

[Thunderduckie]

I should clarify..... By saying spark advance all the way up or down I mean the position of the lever, not the advance itself.

[Greg Jones]

Your point gap is a little wide-range should be 0.018 to 0.022. A wider gap will advance your timing. Your rotor to cap gap should be a minimum of 0.025 and some go wider. Do a search on timing posts on the Model A forum posted by Purdy Swoft and Tom Wesenberg. Pay close attention to what they say about taking backlash into account.

As to vacuum I have never used a vacuum gage on a Model A so am of no help there. Regarding the spark advance lever: if you have a stock 4.22:1 Model A head, then advance to about 3/4 or slightly more for highway speeds. Higher compression heads require less advance. My 5.5 Snyder head on one engine I can advance to roughly "2/3" while my 6.0 Snyder on a different engine runs best at highway speeds (55 mph) just slightly under 1/2 advance. YMMV as they say......

[Bob C]

Here is a link to the Owners Manual, see page 10 for spark control.
http://www.motormayhem.net/wp-upload...ion-Manual.pdf

Bob

[Greg Jones]

Timing a Model A is really simple. 1) set point gap properly 0.018 to 0.022", I shoot for mid-point 0.020." 2) find top dead center using the locating pin in the front timing cover. Ask if you don't know how to do this. 3)Adjust rotor so that the trailing edge is aligned with trailing edge of #1 contact in distributor cap AGAINST THE BACKLASH. This means if you have slop in your distributor shaft, turn it counter clockwise and make the adjustment. When you let go of the rotor it may spring a little counterclockwise. Don't make the adjustment in the counterclockwise position, turn it clockwise to align it. Clear as mud?

Geez, I am starting to sound like Purdy and Tom Wesenberg! But that's OK, I could do far worse. (Hopefully I said everything correctly-it is late and I am tired.) There are of course more "precise" methods of timing but ever since I followed Purdy and Tom's advice, my Model A runs 160-180 degrees and with more pep than I ever believed capable. 55 mph is really no sweat now-I don't go faster because I need new tires!

[Tom Wesenberg]

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My engine is stock and I start the engine with the spark lever full up. As soon as the engine starts I pull the lever half way down. While driving and stopped at red lights I leave the lever at 3/4 of the way down. For climbing hills I will retard the timing some. Full down is 40* advance, and that's more than you need and may hurt the engine.

If you have a higher compression head, you need less advance.

[Mitch//pa]

the wrench gets you very close but not exact... usually i am a degree off using it..
yes the car will run good that way but i like to be spot on..
i only use my vacuum gauge for checking mechanical fuel pressue on later cars. never for diagnostics of engine related drivability..

[Kevin in NJ]

You can time the engine using vacuum.

Just look it up on google.

Here is one example: Vacuum timing

[Jacksonlll]

Your timing is either correct or it isn't. Simply put the engine at TDC and with the key on, the spark lever full up, and a test light connected to ground and the passenger side of the coil, (the light should be off), pull the spark lever down two clicks. If the light turns on, then your timing is right on. If not, adjust it. A retarded spark will make you run hot.

[marc hildebrant]

I would strongly suggest that you time the car the way that Ford used in the service/car manuals.

The best method is the one found at http://abarnyard.com/workshop/workshop.shtml

run by Marco T., a member of the forum.

Marc

[barkleydave]

Thanks for posting the manual. New to the A. Was told to run with spark full advance. I think my engine runs a little warmer than others. It is tight from new rings,pistons, babbit. It is hilly in KY so is it better to have it retarded going up these long uphill grades?


I am not able to run with GAV 1/4 open seems too lean. It likes 1/2-3/4 much better. If I open the carb needle valve adjustment 1/2 will that change my GAV setting and put it near specs?

Thanks

[Mike V. Florida]

Since the use of a vacuum meter was mentioned I though this may be a good place for this;

[Old182]

FWIW: I run a vacuum gauge in my coupe and at idle it reads about 15"Hg with the spark fully retarded and about 17"Hg lever down (it dithers a bit). There are a few hills around here that my car doesn't like and it tends to barf coolant out the radiator cap near the top of one of them at full throttle and makes a mess. With the vacuum gauge, I can run slightly less than full throttle (about 2"Hg) and keep the coolant where it's supposed to be. Keep in mind that just because your gas pedal is not touching the floor doesn't mean you're not at full throttle - but the vacuum gauge tells you where the throttle is. Also, if you know your vacuum and you have some idea of the barometer, you can easily calculate manifold pressure, an indication of how hard you're running your engine. Barometer + the vacuum reading = manifold pressure, e.g. 30.0 Baro + -10.0 Vac = 20.0 MP. With all due respect to the folks on this forum who are much smarter than I, I was taught in 1960 to start the engine with the lever up and pull it down when the engine fired and this engine has been run that way ever since with no problems. Model As are very robust and forgiving machines. But I do run the lever up a little at high vacuum readings (low loads) and slow speeds. I like having vacuum data while driving but I don't know why anyone would time a Model A engine any other way than Henry's and I couldn't tune an engine with a vacuum gauge if my life depended on it.

[Thunderduckie]

Thanks so much for all the helpful information guys. I'll make adjustments this weekend and report back with my progress.

[Bob Bidonde]

Timing the ignition by vacuum is an indirect technique because there are other variables that impact manifold vacuum. Do it the Ford way and then tweak the ignition timing to find the sweet spot for your particular engine. Generally, more spark advance is practical with modern gasoline.

[40 Deluxe]

The best way to time an engine with a vacuum gauge is to place the gauge on the ground directly behind the right front tire, start the engine, engage reverse and back the car up about six inches. Shift into first gear and drive forward about six inches. Repeat until vacuum gauge is completely flat. Proceed to set the timing per factory method.
There are too many variables in play to accurately set timing by vacuum: Worn intake valve guides, worn rings, slop in carburetor throttle shaft, idle speed, compression ratio, non-stock or reground cam, worn cam, worn timing gears, your altitude and atmospheric conditions, and maybe more.
All you're doing is setting base timing anyway, just like in a later model car. Whereas a later model has centrifugal advance and vacuum advance (now computerized), you have the advance lever! Once you move that lever, you are no longer at base timing, so all that fiddling with a vacuum gauge just went out the window! In a way, your 'A' has computer controlled timing! (It's that gray computer between your ears.)