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Unread 04-20-2013, 02:09 PM   #31
86cj74.2L
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If you take the metal cover in front of carb off you will see the two plastic arms. One is for the accelerator pump and one is for the needle assembly.

Needles are in the middle.

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Unread 04-20-2013, 02:29 PM   #32
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Does anyone have pictures? Any instructions of the proper technique for setting these? I've searched for accelerator pump and haven't seen a good description of what that does.
Thanks again everyone.
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Unread 04-20-2013, 03:39 PM   #33
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Quote:
Originally Posted by 4Hamsters
Does anyone have pictures? Any instructions of the proper technique for setting these? I've searched for accelerator pump and haven't seen a good description of what that does.
Thanks again everyone.
Look for manuals. There is a Carter manual and the factory service manual has it too.

Both are linked for downloads in here somewhere.
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Unread 04-20-2013, 05:25 PM   #34
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WARNING: I know very little about the technology of carburetors but I think they're extremely interesting and clever, so, I'm trying to learn. For those who are experts, please correct the following, if you can stomach reading through my likely misunderstandings!

Is this what we're talking about? (Image Below) The main jet has a (two?) long vertical needle(s) that extend down into the different circuits controlling air/fuel flow available for idle and low speed circuits? (0 to 3/4 throttle)

main-jet-adjustment.jpg

If that is true, having these adjustment screws too far out (turned CW too far, LH threaded) would allow too much air into the mixture, proportionally leaning air/fuel during both, idle and 1/4 to 3/4 throttle. Meaning,
  1. I would have to set my idle screws extra turns out (toward a rich condition) to make up for the lack of fuel from the main jets. But, since at idle, there exists this separate system (idle screws) and bountiful vacuum, a rich enough condition can be created to sustain a smooth idle. If you can recall, my current O2 sensor reading at warm idle is in excess of 0.9V.
  2. I would not, however, have a system outside the main jets to compensate during the low speed circuit operation (light to moderate throttle). This would leave me to a lean condition during most of the engine's operation, explaining why the O2 sensor has indicated such horribly low readings during cruising and light acceleration.
  3. The high speed circuit (which I haven't looked closely at, yet) remains independent enough to supply ample fuel during WOT operation. Hence, my readings of about 0.75-0.85V when fully opening the throttle.
How does all this sound? Am I or ?
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Unread 04-20-2013, 06:49 PM   #35
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You do not have that setup. All of your adjustments limit fuel flow.

Your carter is a solid fuel design. Look at the top of the needle assembly. You will see a Allen screw. Turning that moves your needles up and down in the main jet. The higher the needle is at any given time compared to where it was will add more fuel. Those needles track the butterflies. Raise the needle untill you see .45 at 55mph and then slow down and check the readings at 25 and 35 and 45 too.

Try making your idle .85

what is your idle rpm?
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Unread 04-20-2013, 06:59 PM   #36
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Those needles control the fuel metering while their inside the main jets.

The idle screws only effect idle. They are basically turned off at lower vacuum levels. (Because of the air bleeds that determine at what vacuum level the different circuits are effective)

The needle position inside the main jets (limiting fuel flow) and the air flowing by the throttle plates determine your air fuel ratio.

But mind you the O2 sensor is only reading the gasses coming out the exhaust. If a cylinder is not firing properly it will show up as a lean twitch. Also the reversion will draw fresh air into the exhaust showing a leaner condition than what it actually is.
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Unread 04-27-2013, 08:01 PM   #37
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Eugene,
Do you remember back when you were adjusting your main jet needle assembly what the magnitude of the adjustment was? Like on the order of several turns of the Allen screw or like an 1/8 or 1/4 turn?
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Unread 04-27-2013, 09:38 PM   #38
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Quote:
Originally Posted by 4Hamsters
Eugene,
Do you remember back when you were adjusting your main jet needle assembly what the magnitude of the adjustment was? Like on the order of several turns of the Allen screw or like an 1/8 or 1/4 turn?
Small amounts. Like 1/4 turn then test.

It's easy to take the Allen wrench to adjust the needles and a small screwdriver to remove the access plate and make a adjustment, and see how it Changed the O2 reading. Then find a place to stop and try again.

Lifting the needles is richer. Dropping is leaner.
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Unread 04-28-2013, 03:55 AM   #39
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You don't remember which way lifted the needles, CW or CCW, do you? I've see some texts for carter BBDs that say the Allen screw is LH threaded.
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Unread 04-28-2013, 12:13 PM   #40
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Counter clockwise is lean and clockwise is rich
image-3969295329.jpg  
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Unread 05-03-2013, 06:24 PM   #41
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Well I tried adjusting the needle assembly today. Since I was so lean at cruise, ~0.01V, I decided to make a large first adjustment. I turned the allen screw 1/2 turn CW, to enrich the mixture. When I took it for a test, at about 45 mpg and 1/3ish throttle, the reading wasn't much better, maybe 0.04V.

How much adjustment should I expect from this screw? (I don't want to back it all the way out, being LH threaded.)

At any rate, I was convinced I needed to retrace my vacuum setup and really open my ears. At idle, I noticed a hissy but couldn't pin point it. I used the brake cleaner and sprayed in all the spots again but no stumble whatsoever.

So I was frustrated and decided to try and simulate capping off vacuum lines by squeezing them closed with my fingers. When I got to the vent from the evap canister, the idle quieted and the meter jumped from 0.95 to 1.05V. Also, I could start to hear the PCV start to jump around. I knew I'd found something, so I verified with Dale's webpage, adventures under the hood, and confirmed that the canister has a bad diaphragm under the cap.

This explains why I couldn't find it with the brake cleaner, and why my idle screws are backed so far out, most likely masking the leak. (Sorry Eugene, I know you pointed this out on page 1 or 2! )

Anyway, does anyone have a part number for this canister for autozone/advanced/oreilly's/napa?

(Eugene, I'll cap this vent to the carb off and retest the needle assembly position.)
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