It is time to evaluate and possibly rebuild the distributor.  It is possible that the 18 degrees you observe is not initial but it is much more believable.  You've identified a problem.  Fix it and see if your initial advance becomes more realistic and mileage increases.



Lawrenceville, GA

Checked firing order, distributor positioning, and TDC marks (again) and everything was as it should be.  I think I may have at least a partial explanation though.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Pete, I agree that something is wrong with the picture.  I'm hoping with the help of this forum I'll be able to find out what that is.I'll double check my firing order first thing tomorrow.  I know for certain that all cylinders are over 150psi compression so that's not the problem.  The camshaft will be harder to check.  I do know that my vacuum gauge always reads very smooth and steady and that engine power and responsiveness are good.  I didn't observe any red flags when I had the cam out but I didn't measure every lobe either.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

peeeot

I agree with Charlie that an engine with normal compression ( 120 psi or higher ) will be almost impossible to start with 25 degrees BTDC. It will kick back cold and not turn over with the starter when hot. Either your firing order of the sparkplug wires is off one plug or your camshaft is flat or the overlap ( intake valve open while the exhaust valve is open ) is excessive.

Something is wrong with this picture.  Pete

Charlie, that 25 degree initial is with the vacuum advance disconnected.  I assure you that the timing marks are accurate.  I have used different timing lights as well so it isn't instrument error either. 

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Initial timing has nothing to do with the internal advance mechanism (I'm assuming that is the timing plate) and you can set it to whatever you want so long as the engine starts and runs properly.  25 degrees is not very realistic, but it is possible.  My thought is that it's not actually 25 degrees and something else is going on to make it appear so.  Maybe that is with the vacuum advance connected?



Lawrenceville, GA

Peeeot , How can you be setting it with a 25 initial? With anything other than a modified timing plate set with 12 degrees in it, it would have be detonating badly, moreso if in by 2500! ?  DO you have a good 10 or 20 X magnifying glass with a light to check you plugs for detonation? Im not really sure of your fuel over there but I just checked my settings the other day, because we where discussing this. I have  [with a modified timing plate]  13 degrees initial , total timing at 38 degrees [that surprised me ; o P ] all in by 2750 rpm and with vacuum 50 degrees total. Pertronix ignitor 3 and matching coil, Car runs on the rich side, has a PCV, motor would be worn..
 When on the freeway I had to stick my foot into it [not to the floor] and I heard a little detonation with that, maybe there's a  mechanical / vacuum crossover?  Some plugs did have one or two dots , nothing major I might knock 1 degree off and see how that goes.
Vacuum is around 19- 20 out of gear idle, in 16-17,  general cruising around 18  knock 2 off that for higher freeway speeds. 

those figures you quoting are standing still with no load on it , Im sure it would change with driving. 



"Came too close to dying to stop living now!"

I understand a bit better now why the prevailing wisdom calls for 36-38* mechanical advance in by 2500 + 6-8* vacuum advance.  I used my vacuum gauge and timing light and tachometer and mapped the maximum vacuum in increments from idle up to 2500 RPM, and at what advance range that maximum was attained.  From 1500 RPM up, the engine was happiest (about 23"Hg) right around 45*.  Anywhere from 40-50* seemed about the same as far as vacuum, engine speed, and smoothness but I thought it sorta peaked in the middle of that range.  Below 1500, it wanted 35-40* as low as 900 rpm.  

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Ted, I'm not using a dial-back light.  I measured the scale on the damper and marked out an extended scale up to 50 degrees.  As for total timing, the most I specifically observed was 35 degrees mechanical.  That was with 9 initial.  I don't know the rpm I saw that at because the tach I was using to map advance points maxed out at 2000 rpm.  Once both springs came into play around 1200 rpm the advance rate was very flat, so I expect there was more advance left in the distributor, but how much exactly I don't know as I didn't want to overrev the engine.  In taking the initial up to 25, that would bring my total advance to 51.  It is an original distributor, not the service-replacement later style with the triangular shaft.  I seem to recall reading something about these dists. having a pretty high limit as far as advance range.  Poor quality fuel is a possibility.  All the pumps in central NC "may contain up to 10% ethanol."  I prefer to use Shell or Exxon though I will fill up with others if convenience dictates.
Roger, no offense taken, sometimes with things like this it's hard to be satisfied unless one runs the tests oneself.  Especially when the results are wonky.  I think that rather than sending the unit off to be calibrated on a machine, I'm just going to calibrate it on the vehicle.  Apparently my engine has "special needs," doubt I could anticipate them well enough to get the curve right without road testing.Talkwrench, it's a 1957 Carter AFB with vacuum secondaries.  Correct model number for 1957 312 Fairlane.  I even verified all the jets and rods and such with a '57 Carter data sheet.  Car should weigh about 3500 lbs according to specs I've found.  Nothing too extreme. 

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Did I miss what sort of carby you had?  I don't think you have anything going on abnormal.. But you have a 57 , auto, its a big car, how much does one of those weight?



"Came too close to dying to stop living now!"