Quote from: Roland on April 16, 2014, 03:22:34 PM

PS: Chet, I did a complete restoration on the Engine, so it should be mechanically okay.

Roland,

Happy Easter to you also.  In your first post you said the engine misfires.  Based on you statement about the rebuild could you have a bad distributor coil ?  Is the misfire occasional or is it constant and power draining ?  How is the vacuum, is it reasonably steady ?  Does it misfire at idle ?  Bad wires or arcing in the distributor cap ? Why do you suspect carburation ? 

Just curious,

Chet...

Quote from: imoore on April 16, 2014, 05:06:00 AM
I have always been taught to disconnect the vacuum line when setting ignition timing with a vacuum advance.
As far as I'm aware vacuum  advance  system only take control of about 5deg of advance then the centrifugal advance takes over.

Not much help but its all i got at the moment.

Ian

Roland,

Ian makes a good point.  With the vacuum advance there is also a centrifugal timing advantage created by springs and weights.  This produces timing advance while the distributor is turning even at idle.   This combination of centrifugal advance along with the vacuum advance gives you the timing over a full range of engine rpm.  Here again I have not seen your distributor so this is all theory.

PS...   As mentioned in another post, these engines are old and there is a lot of slop in the mechanics.  The timing method will get you a running engine.  Tweaking the distributor in one direction or the other to smooth out the engine speed over your driving range would be something beneficial to try.

Good luck, Chet...


Chet...

Hi Roland,

I am not familiar with the vacuum advance on the 31 PA but in the full advance position the plugs should fire before TDC.  So in answer to your question I would say set the Ignition timing (0.046" before TDC) in the full advanced position.  The plugs should fire slightly after TDC (Fully retarded) in the crank position.  This should help eliminate kick back.

Logic would dictate that without vacuum the distributor should be in the full retarded position.  That is with the motor not running the distributor should be fully retarded.

Based on the statement you copied from the book:

The owner's manual (Page 42) is also contradictory on this point:
"Spark Advance (Automatic): For all road driving conditions the spark is automatically advanced by the engine speed. A mechanical-vacuum control retards the spark at low speeds when the throttle is closed and the engine is idling. When cranking the engine by hand, the spark is in its **full retarded position and advances the moment the engine starts to run under its own power."

My assumption is that any small amount of vacuum will advance the point plate to a run position.

I am sure someone more familiar with your distributor will chime in.

Chet...

racertb,

All you can do now is fix the things that you can see which are obviously a problem than go from there.  As soon as the points open the ckt should fire.  The point gap only needs to be open long enough to allow the coil to discharge fully and to ensure that the points stay closed long enough to recharge the coil.  The differences between .016 and .018 are functionally negligible.

Chet...

Racertb,

Ian & Old Man have given you some good advice.  Based on your statements in both emails here is my take.
Your statement "felt a slight loss of power then some misfiring and then a few loud bangs/backfire, but not from all from the exhaust."  Based on other statements this leads me to believe that your timing had changed dramatically and was shifting from before and after TDC.  Many things can cause these symptoms but the advice to check the distributor time gears seemed real good to me.

Your next statement "Tried to restart several times, finally started and ran for a few seconds then shut off again.  Some more backfire."  Backfiring through the exhaust is the plug firing with the exhaust valve open and likewise backfire through the carb is the plug firing with the intake valve open. 

When your engine is cranking and appears to slow instead of start you are firing the plug to much in advance of TDC.
In these combined instances I would suspect a catastrophic time issue which could be timing chain or distributor.  In the case of our old motors the distributor timing gears should be checked.  (As Old Man Mentioned)

The other issues with poor point timing or a shorted distributor coil may have been caused by the trouble shooting process.  Ian troubleshooting process is a good one to follow.

My 2 cents

Steve,

When working with these old cars and especially the old wiring there are two basic issues that you will run across.  First, poor and deteriorating insulation of your old wiring leading to short circuits.   Second, corrosion at switch and contact points leading to high resistance at these points which results in very dim or what appears to be nonworking lights or accessories.

If you are not familiar with DC circuits and wiring it might save you a great deal of time if you google "Understanding DC circuits".  Knowing the practical relationship between resistance, voltage, & current will save you hours of project time.

An example.

http://www.school-for-champions.com/science/dc_circuits.htm#.U0Z5rHJOXDc

I hope this helps,

PS... As previously mentioned, check the Tech Section for the switch wiring diagram.

Chet...

Steve,

You are missing something and this is keeping us from helping you and its keeping you from solving the problem.  Without seeing what you are missing we will never come up with a solution.  Please send a picture of the coil from both sides (front of the firewall & back of the firewall) and a picture of the distributor looking down on it with the distributor cap off.  This picture should also show how the capacitor is wired.  A manufactures name on the coil would also be helpful for research.   

The distributor should be providing an on/off function to the coil to allow it to charge then release charge when spark is needed to fire the plug.  We need to figure out how this is being accomplished than we can fix your problem. 

Have you seen this motor running before you took it apart ?

See picture below.

Hi Steve,

If you review the diagram that the Old Man provided it is not beyond the realm of possibility that power could be applied somehow or somewhere to the casing of the coil.  Clutching at straws here.., that is why a picture of what you have is so very important.   If you have trouble posting the picture email it.



Old Man, great diagram.

Chet...

I found this explanation of point dwell.  I thought you would find it interesting:

At ordinary engine operating speeds, the points open and close a couple of hundred times per second, the exact number depending on the number of cylinders and the engine RPM. The points need to be closed for an appreciable time in order to build up the maximum magnetic flux in the ignition coil core.

The period of points closure is specified by the ignition system designer and is typically expressed as degrees of distributor rotation. In a four cylinder engine, the angle between each ignition cam lobe is 90° and the period of points closure or "DWELL" is usually a bit over 45° of distributor rotation. In a six cylinder engine, the lobes are 60° apart and the dwell time is 30° to 35°.

The dwell is adjusted by setting the points gap to a specified distance at maximum opening. A narrower gap gives more dwell and a wider gap gives less. Taking it to extremes, excessive dwell means that the points close too soon after opening, cutting off the magnetic field collapse before it delivers all its energy. Too little dwell gives the magnetic flux insufficient time to build up to the maximum.

Both conditions give a weak spark which gets even weaker as the engine RPM rises and produces misfiring at normal operating speeds. The dwell, as well as spark plug gap, do have an effect on ignition timing. The later the points open, the later the spark comes and retards the timing. The earlier the points open the sooner the spark comes and advances the timing. That is why timing is the last thing to be set in a tune-up.

Steve,

Your coil has to have another connection point somewhere probably from the key switch assembly if they are one and the same.  A picture of the coil assy. would help.

OLDMAN  FYI

It is true that technology assists invention.  The spark coil goes back to experiments by Tesla in the 1800's.  The spark at the plug point is created by the collapsing field when the coil is opened.  Voltage is defined as = Change in Magnetic flux / Change in time.  Voltage in the collapsing field = Delta fe/t  when the switch is opened voltage is driven to infinity because you are dividing by  t = zero.   This gives you the momentary spike near 10,000 volts with minimum current that you see at the plug.  I can go on for hours about radio.  BTW... the coil actually has two windings which aids the step-up of the output voltage spike.  I think this is what Kettering added or used to perfection.

It is sometimes referred to as a Tesla Coil

Update before rebuttal:

I guess to be really accurate you need to go back to the early 1830's and Michael Faraday and Joseph Henry.  Both are attributed with the laws of induction.  I personally always equated the distributor coil to Tesla but Tesla's device maintained the transient in resonance.  Just goes to show that things build on other discoveries.  Without these guys Marconi would be making pizza.   Sorry for the regression, I landed my first job as a field engineer explaining induction about 40+ years ago to a hiring panel.  Just had to chime in.

Chet...

Do you have a separate ignition switch and coil.  On the 29 they are a one in the same unit.  I would assume the 28 is similar but I have not seen a 28 ignition setup.

For the 1929 Plymouth, One side comes from your Amp meter and the other to the distributor.  see diagram.



Consider the points a switch that turns the coil on/off.  This on/off action creates the spike that fires the spark plugs.

Chet...

Is the Fedco Serial Number Code readable from the dash emblem.  From this we can estimate the month & year of manufacture.

Could it be a Standard Coup rather than a Roadster ?  Do you plan to do anything with it.  It looks like it has been stripped for parts.

I think the Mile-O-Meter was designed to help the driver improve his driving skills to increase the drivers miles per/gal.  I don't know when this was out as a product but I would guess late 50's early 60's.  Of course it is a very good vacuum meter and has a large scale to detect leaky valves and other vacuum related issues.   I will have to pay more attention to vacuum readings next time I tune my old engines.  All that has been discussed makes good sense to me.

Thanks,  Chet...

I picked up this "Mile-O-Meter" a while back.  Based on this discussion I will have to put it to the test. 

Now I need to figure out what I did with it    Using it to tune the carb mixture sounds good to me.



Every day is a learning experience.   Tks Chet...