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55 century carbissues


gmeyer316
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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

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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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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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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.

 

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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found a little vacuum leak where the line goes through the firewall. Idles good now in neutral, idles rough and slow in gear.

 

 

Ok, a vacuum leak can ruin a whole day.   Determine one more time there is no other vacuum leaks.  Additional air coming from anywhere other than the throat of the carb will make idle rough and lean running.   Once you are sure there is no other leaks adjust the fuel mixture screws again as well as the idle speed screw.

 

And to be sure, the carb has been off and all the screws keeping the entire carb together have been snugged up?    

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doesn't idle rough in gear it just dies, do I need to bend it back again like it was?

That would be my first move. Or just leave it straight, take the cover off and adjust the pump arm to compensate for the position change that occurred when you straightened it.

Edited by smspaul (see edit history)
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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

Did you do all of this?

Your rod was bent incorrectly. Why would you bend it back?

Edited by buick5563 (see edit history)
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Don't run away, dammit!!!

I have two more questions.

Where does that hose go from the left oil filler?

What is that Home Depot plumbing piece on the intake manifold vacuum port?

Neither are stock.

I wouldn't trust the "freshly rebuilt carb", while we're at it. The upper gasket looks to be enhanced with pookie (gasket maker) of some sort. That is some rigged BS if it was really used.

I AM NOT slamming the OP asking questions. I would just like to make sure the answers he is receiving are being tried.

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Good eye Mike and those may be pics of my engine you're referencing instead of the OP.  They were meant to show how the pump arm looked without a bend, the linkage, and the return spring attachment points.  The hose from the oil filler cap and the T off the intake manifold is where I plumbed in a PCV (selected to pull minimal vacuum) on the car because I didn't want to bust into the back of the valley pan where the road draft tube is.  This keeps the blowby oil film from getting all over a clean engine compartment when driving and works pretty good.  It comes off and the regular oil cap goes back on for shows and just disconnect the T.

 

Back to the post, I also think its best to keep the pump arm straight since the lever that the linkage attaches to is swaged onto the pump operating shaft, so if anything this resulting subassembly should be back in its proper position.  My expectation is this adjustment would only have an effect on acceleration and not idle.

 

The hex idle speed screw only going in a half turn before bottoming out doesn't sound right - seems my recollection is 1/4 turn is about 50 rpms but don't quote me on that.  There should be a few turns of adjustment left in it rather than half turn. Think mine is only 1 1/4 turns in from when it contacts the throttle lever.  Maybe when the cold engine is running on the fast idle cam there is enough throttle applied to keep running while stopped in drive.  At hot when it comes off the cold cam and drops against the low speed hex screw it might be too slow.  Slow enough that it can keep going in N but not with the load in D.  If the screw is really "in" that far and is properly mounted in relation to the throttle lever then the carb is likely running off the main circuit with the throttle plates cracked open enough that its bypassing the idle circuit. Or maybe the threads on the hex screw are compromised and need to be cleaned up.  This doesn't yet explain why it worked earlier then "started acting up".

 

One could also back out and remove both mixture screws (after counting how many turns in until they seat) and shoot some compressed air in the circuit at about 10 psi.  That has worked for me when some crud made its way past the glass bowl fiter and screen in the carb messing up my idle circuit.  Got lucky and avoided having to dig into the carb.

 

Numbers would really help narrow down the problem.  Hoping we'll see some warm idle speed, timing, vaccum and/or dwell measurements and how good the fuel and fuel filtering is.  Lots of experience available on the thread to solve this.

Edited by KAD36 (see edit history)
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Most "pookies" are not gasoline resistance, much less ethanol resistant.  Hence, it all needs to be cleaned up/out and removed soon.

 

Just soaking the carb and putting a fresh (new, not NOS) carb kit with a QUALITY (correct OEM thickness!!) base gasket only means you've got a "clean carb", but (as mentioned in my earlier post) will NOT address any hidden "deposits" which the carb cleaner will not dissolve or remove.  Whether it was a "Professional" that rebuilt it or anybody else.

 

NTX5467

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Ok. So we have not established anything yet. Let's assume for a minute that the carb is ok (after rebuilding it again without gasket maker and no gas seeping out of the carbs fuel inlet screen - both visible in post 10 ) and the timing is good.

Next thing to do is de-rig the intake manifold T. Even without seeing the rest of the engine, here is my guess. That plumbing pic (post 10 passenger side) is a vacuum hose going directly to the wiper instead of through the fuel pump. The wiper is probably leaking. There is a vacuum leak.

Yes?

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