Hmmm, 1 turn out with idle screws seems lean, have you tryed with screws out about 1 3/4 turns and reset idle speed and timing and see if miss occurs. Although i see you have tried with another carb. I,m starting to run out of suggestions.:

  AussieBill            YYYY    Forever Y Block     YYYY

 Down Under, Australia

Pete, I know this has been asked (almost everything that would affect it, has been) but how are you sure the marks are correct? The comment about 20 degrees making it run better has me wondering. My own F code loves more initial advance, I have it set on 16 degrees but it would love more. Remember F codes are only around 8:1 though I can't see that making a lot of difference.

To me, it's beginning to sound as though the damper is wrong. The vacuum drop might be attributed to the vac advance retarding as the vacuum falls, which creates a further drop in revs, which creates lees vacuum etc, etc ad infinitum. I know that does not help with the vacuum disconnected, but it's the best I have right now.

Frank/Rebop

Bristol, In ( by Elkhart) 

Aussiebill, the factory data sheet calls for 1 turn initial setting and a final setting range of 1/5 to 1 1/2 turns. It's funny because the carb that was on the car when I bought it would not run in that range, requiring at least 2 turns to run at all, whereas the current carb slows down noticeably with anything more than .5 turns, as long as the main fuel circuit is not in play. I even tried swapping the primary booster assemblies from carb to carb to see if that was where the difference was, but it didn't really change anything.

Pegleg, to check the timing marks what I did was to remove spark plug #1 and stick a screwdriver in the hole with my fingers against the head holding the shaft of the screwdriver. I slowly turned the engine with a wrench and socket with my other hand and tried to get a feel for where the piston stopped moving upward and where it started to go back down again, knowing that TDC would be in between. It is not the most precise way in the world but when I would think to myself "this should be top" I would look at the pointer and it would be very close to the TDC mark, within a few degrees. I tried it a few times consecutively and the result was consistent.

I am very discouraged. There have been so many times that I thought "aha! A new angle that hasn't been considered yet. Surely this will reveal the problem!" only to end the day with the car unable to move under its own power yet again. I just don't understand how so many changes, adjustments, replacements, and experiments can fail to yield any conclusive sense of what is wrong. I have been thinking about it so long that I don't even know how to get a clean slate in my mind or a fresh perspective on how this problem could still exist. Those vacuum gauge videos are about the only thing I can think of that one of you might look at and be able to see something right away that I'm not recognizing.

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

Some times the best thing to do is step back for a while. The approach it as a new problem with a fresh mind. We can get so wrapped up in what we have done that we miss simple things.

I did a tune on on an Olds years ago. The regular points, plugs, condensor, cap and wires job. When I went to start it to set the dwell and timing the engine would not start. I went over everything I had touched probably 20 times each. Reset, re gapped, etc. etc.. After a couple of hours my buddy walked in and I told him the monster delima I was having. He took a quick look and said "did you check the coil"? Of course I hadn't, put a used coil on and started it right up. The symptoms were all there but I was so focused on what I had changed on the car I couldn't see it.

Anyway, thats my story for stepping back a bit. Hope this helps. Leave it for a while, come back fresh, and start the troubleshooting again. Good luck. Chuck

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

6.2v is fine, I was just curious as I also have a Mazda rx3 that has a rough idle & misfires from 6000 to 8000rpm. With its twin ignitions it does make diagnostics more difficult, but on testing the coils I found one of them was only at 4v on the points side, the spark plugs that are run by that coil kept fouling as well, although I haven't changed the coil yet to see if that fixes it or not I have also noticed when I turn my headlights on the idle drops about 100rpm & that's with the regulator set at 14v.

moz. geelong victoria australia.

graduate 1980, bus, truck, car, hot rod, boat, submarine, hovercraft, hydrafoil, firetruck, mobile home, jet, helicopter, cruise ship, motorcycle, bicycle, santa's sleigh, clock, alloy bullbar, alloy fuel tank, lens, dr who's tardis, matter - anti matter warp drive buffer & y-block lover

hey chuck I forgot to put the wire on the points on a customers car once when tunning it pulled my hair out for hours, I didn't notice it because it was sitting next to the points & not touching them, I only found it when I decided the points must be faulty & went to pull them out.

moz. geelong victoria australia.

graduate 1980, bus, truck, car, hot rod, boat, submarine, hovercraft, hydrafoil, firetruck, mobile home, jet, helicopter, cruise ship, motorcycle, bicycle, santa's sleigh, clock, alloy bullbar, alloy fuel tank, lens, dr who's tardis, matter - anti matter warp drive buffer & y-block lover

another thought I agree with bill I would have the mixture screws out a little further than one turn, I know the factory data sheet says that but they can be wrong most carbys like between 1.5 -2 turns out from seated, all carbys are different so I take no notice of the factory data as that is done by engineers in the factory & not under outside influences. the autolite on my 272 has a sweet spot at 2 turns out, in your case at the moment I would screw them in to seated then screw them out slowly until it sounds right & don't worry about the turns out for now. if they run better at 2 turns or even 2.5 then leave them at that for now, remember its only idle mixture, re adjust the idle speed & then that's 2 things to remove from the list.

moz. geelong victoria australia.

graduate 1980, bus, truck, car, hot rod, boat, submarine, hovercraft, hydrafoil, firetruck, mobile home, jet, helicopter, cruise ship, motorcycle, bicycle, santa's sleigh, clock, alloy bullbar, alloy fuel tank, lens, dr who's tardis, matter - anti matter warp drive buffer & y-block lover

Peeot,

From your vacuum gauge readings, it looks like you have a sticking valve in a valve guide. I would suggest you add a couple of ounces of MMO to your gas tank, this should help. As far as your carburetor adjustment, set the idle screws with the vacuum gauge also. Adjust to get the highest vacuum reading and smooth idle, disregard the amount of turns out on the screws as per the manual. The gas we get today is going to run different than the gas availible in 1957. Since your vacuum reading is 21" at idle, your engine should be real close to be in tune. I hope this helps.

JJ

All right guys, I believe I have finally seen what I needed to see to completely be on board with all of you who have pointed to a sticking valve.

I drove the car around and warmed it up and let it idle in neutral, then went out back with a clean paper towel and held it about an inch behind each pipe. Sure enough, right before each miss/spit, the paper towel would suck into the pipe. I wish I had thought to try that a long time ago, as it was very obvious.

Question now is, what do I do about it? I have just added some MMO to the gas and crankcase. If that gets me nowhere, I'm guessing nothing short of removing the heads and having them rebuilt will get me anywhere? Any suggestions?

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

Just thinking out loud - when I adjust the valves on the bird, I use a gloved finger on them one at a time to single out one on the verge of clicking or not. would that help isolate the culprit here?

 
 Steve Metzger       Tucson, Arizona