318 poly w/ carter AFB rough running especially idle and off-idle.

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Evanfrucht

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Hey my 318 poly is running rough especially idle and hesitant/rough when accelerating. It's not terrible but it just doesn't sound or feel right. I'm think the carb may need to rebuilt and already ordered a kit but I have a few questions.
BTW, as of yesterday it has all new spark plugs, wires, cap rotor, points, condenser, and the timing is set to at exactly 15 before TDC. The car has a mild cam (previous owners words) and a cast iron four barrel poly intake.

- I have a carter AFB 9636 which is the emmission control type. How do I make sure this is hooked up to work on my car best. There are 4 various rubber plugs on fittings and I'm not sure if they should be there or what?

-The accelerator pump seems to work when I push the throttle it squirt's gas. how likely is it that is not working well enough? I took the top of the carb off and the plunger seal is not damaged.

- the carburetor is missing it's fast idle rod, is this my problem or do I not need that neccesarily.

- the idle mixture screws seem to seat funny. One mixture screw feels normal: I screw it in by hand and I can clearly feel when it is lightly seated. But when screwing in the second mixture screw I feel slight resitance before it seats. Also when I take it out fully it to inspect almost seems like there is a spiral shaped seating mark. On the first screw the mark is normal. Is my mixture screw seat possibly damaged and how can that be fixed?
 
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The possibilities- bad vacuum advance, vacuum leak, carb, bad cylinder, previous work incorrect.
 
Murray said:
The possibilities- bad vacuum advance, vacuum leak, carb, bad cylinder, previous work incorrect.
Click to expand...
What is the easiest way to test the vacuum advance. I have a fuel pump/vacuum gauge tester and a snap on timing light.

Also I'm concerned about the mixture screw seating condition I described, is that no big deal?
 
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Slowly move the choke closed and see if it starts to clear up at some point. If it does, you've just diagnosed a vacuum leak. Then you simply need to find where it is.
 
Sounds like the idle mixture screw may have a bur on the threads somewhere. As long as the needle end is good, it should seat properly. Does the engine stumble when each screw is seated with it running?
 
RustyRatRod said:
Sounds like the idle mixture screw may have a bur on the threads somewhere. As long as the needle end is good, it should seat properly. Does the engine stumble when each screw is seated with it running?
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When I start to screw in the mixture screws the car begins to stumble and at a certain point the engine will die once they are turned past a certain point.
 
Evanfrucht said:
When I start to screw in the mixture screws the car begins to stumble and at a certain point the engine will die once they are turned past a certain point.
Click to expand...

Good, then forget what they look and feel like. They are working correctly. Do the choke test I described and report back.
 
Cool. Just remember to close it slowly enough as not to stall the engine. You're looking to see if closing it some will make it run smoother. If it does, there's a vacuum leak somewhere. You can zoom in on it with a spray bottle of water. A lot of people recommend carburetor cleaner sprayed around the carburetor base. I cannot, as I have seen a fire started that way. Water will show it up just as well and is perfectly safe. Good luck!
 
OK I will do both the choke and compression tests when I get home. For now here's some pictures I took, maybe someone can see if something looks wrong. There is some sediment in the float bowls. I had more picture with the carburetor top but my phone didn't save them for some reason, I can take more photos if neccesary.

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I did the choke test. Closing the choke fully will kill the engine. I closed it at least halfway and it did not make any noticiabale difference. More hesitation. The car still shakes at idle and the first 15% of acceleration is rough. Also i don't know if this is just how the car is supposed to sound but the exhaust seems to make a faint burping sound what seems like every 1 engine cycle. Im going to check compression now though I have a feeling it will be normal.
 
With a picture of the carb, I can see that you don't have the vacuum advance hooked up. This can cause a stumble on acceleration, but doesn't effect idle. Looking at the carb in the picture, the vacuum advance should be plugged into your plugged port to the left, just above the butterfly ( no vacuum at idle). A side note on your idle adjustment- do both idle screws behave the same? Screwing them in to the point where the engine stumbles- this is normal. Do they both do the same? Or does one side adjust different than the other?
 
My main problem is stumble, hesitation... you may have hit the nail on the head. I have a hose running from my distributor vaccum advance to a fitting just under the choke. Are you saying this is hooked into the wrong spot? I just bought the car recently so I have no idea what the PO might have done
 
You do have the vacuum advance hooked up, but to the wrong port. You have it attached to the choke port. It attaches to the small port on the passenger's side of the engine, in the front.
 
Bingo! I'll see how that works.
(And then what should I do with the choke port?)
And yes both mixture screws respond similarly and will kill the engine slowly when tightned down.
 
If there is vacuum there- plug that port. I don't think you are going to find vacuum there, it should go to a heat source.
 
This means that your vacuum advance has not been working. The vacuum advance is checked by putting vacuum to it and observing the point plate rotate and hearing the engine speed up as it advances the timing. Even better is a small hand-held vacuum pump that will do the same thing but for an extended time that will show up small leaks in the diaphragm. Good luck.
 
I "would" optimize the timing, first. It will probably take more initial timing than 15*. Just something to play around with. Also, you'll want to move the accelerator pump rod to the closest hole to the carburetor in the linkage arm. I see that it is in the hole farthest away from the carburetor. Doing this will increase the accelerator pump shot and richen the pump shot up some. That could also help with the stumble. Generally, tuning works best when you get the timing sorted first and them move on to the carburetor. I attached your last picture. Do you see the red arrow on the right hand side of the picture? Put the pump rod in that hole, instead of where it is.

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