64 Dart 273 Engine Vacuum

Having said all that I thought of something else. Before I would go to all that trouble, I gotta tell you this:
1) if you have a PCV valve, make sure it is working correctly.
2) if you have power brakes, clamp the line shut. If the idle-speed changes and stays changed, that booster is sucking air and needs to be replaced.
3) if you have a 4bbl, make sure the secondaries are closing up tight but not sticking.
4) Your 273 can be adjusted to idle at pretty much any idle-timing from TDC to 20/25/possibly even up to 30 degrees advance. The only thing that happens at idle, is that the idle-speed increases. Conversely, the more timing you take away, the slower it will idle. Knowing this, you can do some diagnostics.
Here goes;
Starting with BOTH the gastank, as well as the floatbowl(s), full of fuel, start her up and immediately, without regard to the actual timing numbers, just rotate the distributor until the rpm reaches a peak, then back it up just a few degrees. Then wait.
If the engine runs beyond the now expected 20 seconds, then we are on to something!
Put post #29 on the back-burner for a bit.
But if it stalls again, then back to post #29.
Assuming it runs ;
Let the engine fast idle until she warms up.
Now;
the fuel in the bowl needs to be in a liquid state and at the proper level.
If it is not, then the fuel drawn up out of the idle wells will not support proper combustion and the engine will labor, or even stall.
So now, after the engine has warmed up, reset the mixture screws to 2.5/3.0 turns from lightly seated, then grab the D again and retard the spark timing until the idlespeed seems normal. REMOVE the vacuum advance line at the D and plug the line. If the idlespeed changed, and it slowed down AND the engine is running rough;
First shut the engine off, and prove your timing index is correct, using a piston stop, on EITHER #1 or #6 cylinder. If it is not correct, and it is not out by exactly 90 degrees, then the outer ring has slipped and the balancer is junk. But if it is out by 90 degrees, then one of two things is at play; 1) either you were not using #1 or #6 cylinder as your reference OR, the balancer is not matched to the cover.... in which case you will have to make a new index.
After you know for a fact that the index is telling correctly where TDC # is; start her up and check the timing. Back up the D until the index is telling you that the Timing is in the window of TDC>5* advance. Now readjust the idle-speed to 500/550 (in P/N with a stock cam).
If the engine is still running and still rough. Shut it off. Now grab your airhose and blow out all the airbleeds without over-pressuring the float bowl and collapsing the floats. Be gentle. Next, remove the mixture screws, and blow those circuits out too. While the screws are out, make sure the needles are not bent or broken, then reinstall them to 2.5/3.0 turns from lightly seated as before.
Now start her up again. If still rough, first prove that the airbleeds are clear, by sticking your finger over them to plug them, one atta time. If the engine idle gets rougher and she wants to stall, then that proves they are... or were working before you plugged them, and that is good news.
So then, now it's time for a valve adjustment and a compression test.
But if now, a big difference is noted, adjust the idle-speed back to 500/550, with the speed screw.
Next, go find that vacuum advance hose and reinstall it. If the idle speed increases, then it is on the wrong carb port; find the sparkport, and connect to it.
Finally, fiddle with the mixture screws looking for "best idle".
Here is where it gets tricky. If the engine like more than 3 turns, then it is not getting enough fuel from the transfers. Simply increase the speed screw setting, just a tad atta time, and if the idle rpm gets too high, slow it down by retarding the idle-timing. Continue until the mixture screws like to be in the 2.5>3.0 window.
But if the engine likes to be in the 2.0 or less range then it is getting too much fuel from the transfers, Simply close the speed screw a little. If the idle rpm gets to be too slow, just advance the idle timing. Continue until the mixture screws like to be in the window of 2.5 to 3.0.
Once you get to this point, she should be idling pretty nicely.

From here, you HAVE to check the power timing, to be sure it is in the window that your fuel can support without detonation. This is usually up to 36* with best pump fuel. Adjust downwards to ELIMINATE detonation.
Once that is done, you the tuner, have to marry the Power-Timing to the Idle-timing, then adjust the rate of advance to whatever your particular engine likes.
Until that is done, make sure you keep her out of detonation, cause that can get expensive in a hurry.

Notice I did not specify any Idle-timing number.
This is because Your Idle-mixture screw fuel delivery, has to be synchronized to the transfer slot fuel , before any idle-timing fussing can be done. After those two are synced up, you should not fuss any more with those screws. If you think you need more idle timing, have at it, but leave those screws synced up. The truth is, that your engine will respond very well to more and more idle-timing, but the Idle-speed rises in direct proportion, so eventually it will be so high, that it really clangs the trans when shifting from N/P to in gear. There is no need for that.
Your engine does NOT care a whit about timing from idle to stall speed. At the Stall is the First time it cares. If you give it too much, it will detonate and simultaneously lose power. If she is short, she will not make optimum power. But she is on the way to about 3500 where the Power-Timing must be optimized. So your window of best performance in First gear is from Stall to 3500. Once you get into Second, having Run First to say 5000, the Rs will fall to 59% with a 904, so to 2950, so that is another point of concern. At WOT now, the Power-Timing has to drop below the Detonation point. Lets say that she detonates at 30*@2950rpm, but not at 28*; so that sets your Power-timing to 28* at 2950 rpm.
So now you are left with Stall to 2950. Again, you gotta stay out of detonation. Say the stall is 2000 rpm, and say she detonates at 24* but not at 22 degrees. Somehow, you have to connect all the dots, which are, say:
36* at 3500, and
28* at 2950, and
22* at 2000, and whatever at idle
All numbers are estimated.
The rates of advance are:
28 to 36 from 2950 to 3600 =8* over 650 rpm, and
22 to 28 from 2000 to 2950 =6* over 950rpm, and
say 5* at 550rpm to 22* at 2000 = 17* over 1450rpm
So then, your Distributor has to be reprogrammed to provide these numbers. Unfortunately, the D can only provide two curves at most, so one of the above has to be reconsidered and the only one, in this particular case, that can be fiddled with is the idle timing to 2950.
The usual thing is to combine the bottom two into one; which is then from
5* to 28* from 550 to 2950=23* over 2400rpm
But, the D cannot easily be made to begin advancing much lower than say 900rpm. So then, the numbers are from 5* to 28* over 900 to 2950, say 2000 rpm.
And that rate is expressed as 23* per 2000 =1.15 degrees per 100 rpm .
The second step is 8* over 650 rpm so, 1.23* per 100 rpm. These two rates are so close that the engine would run fine on just one curve. That would then be from 5* to 36* over 900rpm to 3500, which is then 31*/2600rpm =1.19* per 100rpm.
so back-calculating ;
Idle will be 5*
2000 will be 18*
2950 will be 29**, and
3500 is 36*
That's pretty close to what we needed, namely 22/28/36, and it should work. But as you can see, she is a bit short at stall.
Lets say you really wanted that 22* at stall, with a single rate of advance.
Ok then from 2000 to 3600 is 1600rpm and we want an increase of from; 36 less 22=14*. The rate thus is .875* per 100.
Now we just have to figure out how to get to 22* at 2000 with a constant rate of .875 beginning at 900. That would then take 22 less 9.6*=12.4 * of idle timing. That again leaves just 2950.
Ok from 2000 to 2950 is 950 rpm and the rate is .875* per 100 so 8.3 and add the 22*@ 2000=30.3.... again into detonation....... so the numbers are; 12.3/22/30.3/36
So what do you do?
Let's make the Idle-timing 10*, and the new numbers are
10/19.7/28/33.7.. and yur good to go right? not so fast, yur down 2.3 degrees at 3600, and all your power from there to 5000 is gonna be down.
How much?
IDK but I'll guess 10 hp.
Do you care?
Well unless you are running hiway gears, you will hardly feel 10 hp in First gear. But say you have 3.23s and 24.5" tires. Your stock 273 will power-peak around 4500 and in Second gear at WOT will be around 65mph@ 9% convertor slip, so you know, yeah your ET would see it but will your butt? doubtful.
and if that is what it takes to stay out of detonation, then sometimes you gotta make an executive decision. Yur gonna lose power somewhere with a single rate of advance, the question is where will it be least noticeable?
Now
Please recall; I am in no way implying that this is your car. I picked the numbers out of a hat and just went where it lead me, so that you can see and learn a little bit about timing. This theoretical engine will NEVER be fully satisfied with a single rate of advance. Can it be optimized with a step-rate? I think so but I gotta go, lol.