Timing Light vs Vacuum Gauge ???

[Reg Evans]

How do you guys recommend setting the timing on your old flatties...and why. Timing light or vacuum gauge ?

I haven't done a tuneup on my 35 Dodge for several years and decided to try out my vacuum gauge yesterday. At idle after a good warm up the engine was producing a steady 15" on the gauge. After loosening the dist. and rotating it back and forth I found the sweet spot which was producing a steady 19" on the gauge. I haven't had time to road test it yet or even put a timing light on it to see what I have done but I advanced it a surprising amount to get to the 19".

[oldmopar]

I usually adjust the vacuum by the carb screws once I set the idle and the timing with a light when installing or adjusting points but have seen marking about adjust timing on the gauge so they must be related I guess once the timing is correct the spark improves and produces a better vac reading.

I would be interested what the dwell reading is and what the timing light shows with your method.

[Plymouthy Adams]

like oldmopar, the vacuum guage will allow you to adjust the carb to optimum performance and used with a tach will get the idle speed on the money for checking the timing with a light..reading the guage will also indciate if you are far off on timing to begin with so to roughly set the timing while balancing the mixture and setting idle speed..

[Reg Evans]

Oldmopar & Tim,

I checked the timing after setting the dizzy to get the most vacuum ( 19" ) from the wiper port. Not the carb port.

The timing light is now firing at 10 BTDC and the dwell is at 60 degrees and now it runs better than ever. Wassup with this ?

[oldmopar]

Have you road tested the car ?

[Reg Evans]

Yes, up hill and down hill. No pinging and no real change in power.

[greg g]

Reg you are kinda doing what obd II does with modern cars, adjusting for crap fuel.

The stuff we have today is controled to have a slow flame front and a controled longer expansion of gasses to encourage everything to burn before it gets sneezed out. Think Whooomph and a long shove, rather than Bang and a sharp push. Your advance anticipates the squeeze, and lights the mix when it still being squeezed so the biggest part of the shove comes at or close to TDC.

Also remember that the ethanol cocktail were are being forced to consume has fewer BTU's and runs a bit cooler and increases octane levels so it's a bit more ping resistant the good olde gasoline.

I checked mine the other day with the timing light and I am sitting on 6 BTDC. But last time I messed with it we were still getting gas with out ethanol. Now most stations are posting 10% so I bet I could crank in as much as you are running with out to much excitment.

Edited July 10, 2009 by greg g

[oldmopar]

That is interesting maybe we work too hard at getting these cars running.

[grey beard]

Like a lot of other fellows on this forum, I always leaned toward the idea of power timing - or advancing the timing a ways ahead of top dead center beyond the factory specified initial timing. Having said that, I have found that when you run the additional advance, you will soon be able to see some interesting differences between various tanks of fuel - pick up a lousy one and she'll ping and rattle on a pullm especially at higher speeds. Now, if I had just been satisfied with the factory specs, she'd slog along and not care one whit what was put in the tank - within reason, that is.

Our initial timing specs are around zero degrees advance, or pure TDC - top dead center. Then centrifugal advance adds 20 degrees additional timing that peaks around 2000 rpm, if everything is working properly. On top of that, vacuum advance will add another 18 degrees advance or so, around the same speed, so that when the engine is up around 2500 rpm, there should be a total of around 40 degrees, plus or minus one or two for good behavior.

If you power time initial timing to ten degrees, you will wind up with around 50 degrees total advance. Now stick a lousy tank of fuel in there, and she'll let you know on a hard pull, up around the top end of our highway speed. Might be too much of a good thing . . . . . .

The real trick would be to buy a degree timing light that has a digital readout, so you could set initial timing, then run it up to 2000 rpm and check total centrifugal advance, then hook up the vacuum advance line and see exactly how much total advance you are carrying around with you. I'll bet a whole lot of our cars would fail one or more of these interesting tests, if we could all check them for ourselves.

I even used a protractor and marked off fifty degrees advance on my crank pulley, so I can see with my light just what is working and what's not. Kind of fun to see how much two or three different distributors can varry, in thie timing advance department.

Now if we just had a chassis dyno to tie 'em down on and read real-world back wheel horsepower, wouldn't THAT be fun?

[TodFitch]

...snip... The real trick would be to buy a degree timing light that has a digital readout, so you could set initial timing, then run it up to 2000 rpm and check total centrifugal advance, then hook up the vacuum advance line and see exactly how much total advance you are carrying around with you. ...snip...

Back in 1981 when I got my 1982 Plymouth TC3 Turismo I picked up a timing light from Sears that has an delay adjustment knob on the back. As I recall I needed it to properly time that car. Car is long since gone but I have used it to check the centrifugal advance on my 1933 (no vacuum advance on that car). I just assumed that was what everyone was doing.

For you P15 the manual calls for 16 to 20 degrees of mechanical advance at 2,050 RPM. And it calls for 15 to 19 degrees of vacuum advance at 16 in. of vacuum. If you have a tach/dwell meter and a hand vacuum pump with a gauge you can set up the test conditions. Then with the timing light you can line up the strobe so the marker on the pulley is at TDC and read off the advance.

If you guys aren't doing it that way, how are you doing it? Preferably with readily available (i.e. cheap) tools.

[rolliejoe]

Back when I ran a 340 in a Dart I would set total advance to 38 degrees with the vacuum advance unhooked, was unhooked even necessary? Isn't vacuum

advance more for off idle/ light loads? What's the relationship between vacuum and mechanical advance? Sorry if I'm steering this thing off topic.

[Don Coatney]

What's the relationship between vacuum and mechanical advance? Sorry if I'm steering this thing off topic.

Read this recent thread on the truck side.

http://www430.pair.com/p15d24/mopar_forum/showthread.php?t=16387

[moose]

I've been thinking about it after reading these and a couple other threads in the past few months, and I'm not sure how my motor manages to start and drive everytime I want it to...

It's probably best to keep it in the dark about a few things:

I am for sure not going to tell it that it shouldn't run strong since the vacuum advance is plumbed into the main manifold tube not one of the carbs.

I won't tell it that it doesn't have manifold heat either(it may refuse to run those three days of the year when it needs it!)

Or that it shouldn't go over 60 on the highway because it doesn't have OD.

I won't tell it that the stock points ignition in there should be replaced with an HEI. Or that the dual point Mallory I ran for a couple of years shouldn't have worked because it didn't have vacuum advance!

I won't even bring up the idea that it should be hard to start with a 6volt on cold New England winter mornings.

Probably won't let it know that I should be using a carb synchronizer, timing light, dwell meter, vacuum guage,

and a bunch of other tools that I don't have:(

To get to the main topic of this thread, vacuum advance (as I understand, and have been told for years) is only there to help make smoother the idle/ better low power operation, and for better economy. One of my favorite instructors back in college(Mr. Kam!) used to say that the engineering god gives with one had and takes away with the other. More power, less economy. Better handling, less comfort. With a distributor set up with no vacuum advance(like the Mallory) that runs totally on mechanical advance, if you adjust the timing to the fastest idle/best vacuum, it will ping under load, and it probably won't start again because it will be too far advanced. You get good idling and you lose higher rpm performance. I used to be in the aviation industry and aviation piston engines don't have any ignition advance, mechanical or vacuum. Statically timed to something like 23 degrees BTDC. Long ago for aircraft they chose to have the reliability rather than the limited extra performance over a very small RPM range.

I guess what I'm trying to say is these cars are easy and fun to work on and most of the time require limited tools, some sweat and hard work, and can be tuned by ear. The best thing is pulling up to a traffic light, or at a cruise, or something and someone says "Wow, you keep that thing going huh?" Just feels good.

[Plymouthy Adams]

I have found that for the most part folks don't like mixing engineering facts posted in technical manuals over back yard antics..

[matthewshook]

Is there any harm in using a 12V timing light on our 6v systems?  My father thought there might be, and I just don't know.  I can't seem to find a 6V timing light anywhere, so I'm starting to think that no, there is no difference, but I want some other opinions first.  Dad seems to think that hooking it up to the 6v battery might cause an overload in the gun. It's a craftsman, but I've been known to break thier tools from time to time.

[Plymouthy Adams]

usually the zenon bulb will not flash bright enough if it flashes at all on 6 volt...you can use the 12 volt timing light with an auxillary car battery as the power source..the timing trigger is inductive....

[Jerry Roberts]

The only problem is that the light might be too dim . Thats it . 

[Dodgeb4ya]

I think 12 volt lights double the readings!

[Plymouthy Adams]

HOW....it is an inductive signal...have used mine many times..there is noting to read...only a trigger for the flash...(timing light issue comment in case this infringes on other parts of this thread)

Edited June 22, 2013 by Plymouthy Adams

[Niel Hoback]

  I use a Craftsman 12 volt light on mine and it works very well.

[Merle Coggins]

Yup, 12v timing light will work just fine, as long as you connect it to a 12v battery. I have made up an extension cord for mine that I can plug into my 6-12 volt convertor that I use for my radio. That way I don't have to dig out my 12v booster pack when I tune up the truck.