gmeyer316

55 century carbissues

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55 century 322 newly rebuilt, carb rebuilt, runs great cant get it to idle. Is there not supposed to be a dashpot on carb with automatic tranny?

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Benefits of AACA Membership.

Check the ignition first:  dwell, timing, vacuum advance.  Tell us what carb you have.  I have dashpots on all of mine, but they are not functional.  How many miles on the rebuild?...a very tight engine will not idle well.

Willie

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Dashpot has nothing to do with idle but should be there. It prevents stalling if the throttle is snapped shut. I suggest a vacuum check..........Bob

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Check the ignition first:  dwell, timing, vacuum advance.  Tell us what carb you have.  I have dashpots on all of mine, but they are not functional.  How many miles on the rebuild?...a very tight engine will not idle well.

Willie

X2

 

New engine components need to get to know each other before they will co-habitate well ;)

 

Jon.

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the motor and carb each only have a hundred or so miles on them. runs great during warmup but  when warm just slows down and stops.

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Can you post a picture of the linkage at the carb?  Engine hot, but not running, and aircleaner off.  Both the drivers and passengers side.  It sounds like the engine idle speed screw is backed out too much.

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the only idle screw I can find isn't a screw, its about an inch long and its hexagon with a screw driver slot in one end, it only screw in about a half turn before bottoming and will no longer turn, doesn't seem to help. I will post some pics.

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Is the engine able to run/idle correctly using the mixture screws on the base of the carb? 

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not after its warm. I got the car about a month ago and it idled fine for a while but then started acting up

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Did you check the ignition? Here is a story of one that did not idle but ran well at high speeds:  http://forums.aaca.org/topic/210599-is-it-the-carburetor-this-time/?hl="is+it+the+carburetor+this+time"

The hex and slotted screw you referenced is the idle speed adjustment screw and if it moves the throttle shaft as you screw it in and out it is probably working ok.

After you check the ignition, the carb 'may' need a rebuild (the inside may be as crusty as the outside).

The throttle return spring is in the wrong place, but should work for now.

Check the ignition first:  dwell, timing, vacuum advance.

Willie

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Three things I notice.

That gas looks yellow.

The return spring is hooked up wrong.

The accelerator pump rod looks very bent.

I don't have a pic of those specifics. Maybe somebody else can help you out until I can take one.

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I see in the picture from the 55 buick shop manual that the acc pump rod is indeed definitely way bent, the pump lever is shown as level, mine is not.

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Three things I notice.

That gas looks yellow.

The return spring is hooked up wrong.

The accelerator pump rod looks very bent.

I don't have a pic of those specifics. Maybe somebody else can help you out until I can take one.

 

x3 above and check Willies post on the dwell.

 

Maybe these pics will help:

 

post-76420-0-01732600-1436572661_thumb.j

 

post-76420-0-18235600-1436572669_thumb.j

 

post-76420-0-34387800-1436573121_thumb.j

 

post-76420-0-33798400-1436573113_thumb.j

 

Why won't the idle screw turn?  Is it actually bottomed out (no threads left) or is it bottomed out against the throttle lever and then won't turn?  Should have more than a half turn left on it

Edited by KAD36 (see edit history)

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I don't have the Carter carb on my 56 so pardon my ignorance.  The Carter only has one idle mixture screw?  Does it have a separate Idle speed screw?  maybe behind that small spring down low on the main linkage?

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I don't have the Carter carb on my 56 so pardon my ignorance.  The Carter only has one idle mixture screw?  Does it have a separate Idle speed screw?  maybe behind that small spring down low on the main linkage?

2 mixture screws plus idle speed screw

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My observations . . . if it runs well on the main system, then there probably is NO real issue with base timing, dwell, or similar.  The fact I runs on the main system but NOT on the idle system would indicate THAT's where the issue is.  I chased a very similar problem on a Carter BBD 2bbl on a 1980 vintage vehicle I have. 

 

When I bought it, the seller knew of a carb problem, that it wouldn't idle.  I figured it was just an adjustment, so I was not really concerned about it.  What I did find was that it started fine, ran fine down the road, accelerated as expected, but as soon as the choke thermostat warmed up enough for the fast idle cam to deactivate and let the carb return to base idle, the engine died.  It always restarted, but when allowed to return to hot, base idle, the rpm dropped and the engine died unless I pumped the throttle to keep it running.

 

I went through the carb and found nothing evident that was wrong or out of whack.  I changed the spark control computer, for no change either.  It ran and drove as expected, but letting off of the throttle at 60mph on the freeway (for an off ramp), the car would die.  It would restart as it always did.

 

I pulled the venturi cluster out and used spray carb cleaner to check for restrictions, but had "flow" in all passages.  Still, "no hot, base idle" after the residual carb cleaner in the tubes was used up as the engine ran.  I checked ALL of my service manuals and found an interesting spec . . . "Low Speed Jet" and then finally found out where it was.  This orifice was located at the bottom of the idle feed tube (the small, brass tube extending out of the bottom of the venturi cluster, one for each throttle bore).

 

Recall that I noticed that I had "flow" from all passageways?  That was true, BUT not enough fuel flow when the engine was running!  I also noticed that the specs for this Low Speed Jet varied somewhat from application to application of the same carb series on similar engines.  I found a bent-wire spark plug gap gauge and probed the bottom of the idle tubes, starting with the smallest size.  As I started with the smallest size wire, I noticed a little resistance, which went away with a little effort.  Then the next size and so on.  I, again, flushed the tubes with spray carb cleaner and MORE flow was now there. 

 

Needing to get a firm size of the orifice, I went to a hobby shop and got "a selection" of twist drill bits.  I progressed from the smallest size until I "got brass", then did a little more twisting for a clean and round orifice, with a final flush in both directions.  I reinstalled the venturi cluster, the engine started on fast idle, it warmed up, the choke opened, the fast idle cam would come off, and the engine idled reliably.  I readjusted the idle mixture screws and all is still well, years later.

 

On the venturi cluster(s), there will be two brass tubes on the bottom side.  The small and solid tube is the idle tube.  The larger and "ventilated" tube is for the main system.  On the TOP of the venturi cluster, for each tube, there should be a small hole above each tube, which is the "air bleed" for that tube AND is a fuel system calibration point for each tube.  If those holes are closed off, it will cause that particular system (or side thereof) to go "full rich".  You can use a finger for this or something like a pencil eraser (on the end of a pencil, if possible) to close that hole with the engine running.  IF the speed goes up before it decreases into full rich mode, then the system is "lean".  IF the speed just drops, then the system is either "just right" or already on the rich side.  This can be something you have to play with and experience to really understand how it works.

 

In my case, I got some .020" wire, put a bend near one end, and inserted them in the main system air bleeds on my BBD 2bbl.  I could make the particular venturi have fuel dripping from the fuel exit with a tube in that side's main system air bleed.  Effectively, I was significantly decreasing the size of that calibration orifice, making the system "rich" on that throttle bore.

 

SO . . . I highly suspect you'll find an internal issue with clogged idle speed tubes, internally AND with deposits which carb cleaner will NOT remove, even "the soak kind".  This is why the mechanical method I detailed above is the only way to "get there".  Where I finally found an illustration with the "Low Speed Jet" was in a Carter AFB illustration in ONE year of Chrysler service manual I had, but other Carter carbs seem to have them too.

 

DO go ahead and verify the ignition issues and such, as they'll need to be in good shape and adjustment when the carb is fixed.

 

Keep us posted on your progress.

 

Take care,

NTX5467

Edited by NTX5467 (see edit history)

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Difficult to tell if there is a fuel filter in the glass filter bowl?  Maybe dumb question but from the camera angle it looks empty.  If all you have is that screen that screws into the top of the carb that would allow something to clog up.

Edited by KAD36 (see edit history)

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like I said the idlescrew is a hex shaped thing about an inch long and a quarter inch in dia, it appears to be threaded just on the end and a lot smaller where it threads through the throttle arm, than a quarter inch, does that make sense.

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Start off with the easy things before getting too deep or making too many adjustments.

 

Does it start right back up after stalling out when warm? If so, I think it may be a fuel delivery issue. Watch to see if you are getting bubbles in the sediment bowl when it is running. If not, it may be that fuel tank sediment has gotten into the carb. If you do see bubbles, if there is an in-line filter, that could be clogging up or the sock filter on the new fuel sending unit/pickup may be getting clogged up from old sediment while it is sucking the fuel from the tank. Start from the sediment bowl and work your way back.

 

The low idle adjust is reached from the front, underneath next to the throttle linkage. You have to pull the throttle all the way open to get a screwdriver angled to reach it. This, however shouldn't have changed though since you've had it unless other adjustments have been made.

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Straightened th acc pump rod and repositioned the throttle return spring. Runs better but still hard to keep running at a stop light. Here is a pic with the engine :).post-154034-0-89401300-1436661709_thumb.

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