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AFB accelerator pump not pumping with engine running...Argh!


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I copied this from over at V8buick.com to see if there are any AFB guys who can give me a hand here...I had this thing apart four times yesterday.

All right, this is getting dumb. Basically, when the engine's running, I have no pump shot. If I put it on the bench, it's fine. Here's what I've done...

1. Replaced the inlet check valve. It didn't seem to work well without it.

2. Raised the driver's side float about 1/32", even though it was at spec, just to make sure the well filled. It should fill through the check valve though.

3. I found a couple of float seats that had larger orifices in them, in case the car was dropping the float level too much running (grasping for straws here).

4. I adjusted the pump so it started down in the well as far as I could.

5. The fuel pump has 6-7 lbs. of pressure to the carb.

6. The gas is way down in the pump well. I checked the pump discharge needle and it seemed OK, but I'm wondering if it's maybe sucking air. EDIT: I replaced the needle and there's no change.

The pump just won't shoot with the engine running (or at least it's very weak and sporadic). I'm just about out of ideas here. Maybe the carb has some kind of internal vacuum leak where it's sucking air in the pump system...Any ideas?

OR...anybody have a good 3826S core they could sell me? This thing's never run quite right with the current carb. It came with an Edelbrock, but the switch pitch doesn't match up to that thing very well.

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Did you test to see the floats are not leaking in one or the other. Just a little can goof things up. Also, When you have it all bolted down on the manifold and the engine running spray small fast concentrated direct hit shots of starting fluid along the carb top gasket, the linkage areas, base of carb and see if the idle increases or become sporadic - If so, there are leaks. Also the accelerator plunger may not be true in the bore and when there is a bottom vacuum draw unlike on the bench this will alter the draw capabilities of the plunger. I use to like the leather ones best as the newer plastic skirted ones for use with the corn-ol tend to warp, gouge or leak on a unselected basis ... just some thoughts.

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Hey David,

The car's idling and running great, but there's no pump shot with it running. It does have a leather pump, and I've tried two of them. I tested the floats this past summer by holding them underwater when I went through the carb. I didn't notice the bog so much when it was warmer out, but now that it's chilly, it's quite evident.

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Aaron, this may be WAY off base here as I'm definitely no expert, but back when I cleaned my oiling system and put new lifters in I ended up with one dead lifter. I don't remember if it was on an exhaust or an intake valve but that one dead lifter was causing a serious vacuum problem inside my carburetor while the engine was running. My carb. was operating strangely and fuel was being pulled through places where it should not have been coming from. Once I replaced the dead lifter and all of my valves were operating correctly again, the problems with my carb. stopped. As I said, this may be way off but it might be something to check if all other options are exhausted. Reading some of the other posts above that mentioned vacuum problems inside the carb. made me think about this. Good luck buddy and keep us posted!

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"4. I adjusted the pump so it started down in the well as far as I could."......??? Seems you would want to do the opposite.

Since the well's not filling properly, adjusting it further down the bore gets the plunger closer to the fuel level.

Robert--She's pulling on all 8, and the vacuum is steady. Now my Mustang is currently running on about 5 and a half, but that's another story... :)

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Aaron, this may be WAY off base here as I'm definitely no expert, but back when I cleaned my oiling system and put new lifters in I ended up with one dead lifter. I don't remember if it was on an exhaust or an intake valve but that one dead lifter was causing a serious vacuum problem inside my carburetor while the engine was running. My carb. was operating strangely and fuel was being pulled through places where it should not have been coming from. Once I replaced the dead lifter and all of my valves were operating correctly again, the problems with my carb. stopped. As I said, this may be way off but it might be something to check if all other options are exhausted. Reading some of the other posts above that mentioned vacuum problems inside the carb. made me think about this. Good luck buddy and keep us posted!

You most likely cured the problem when you had to remove the intake manifold to do the lifter work and then had to use a new gasket on the intake manifold upon completion.

Edited by buick man (see edit history)
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