Carb help needed

Theres a lot more then just mixture screws for idle, I learned that yesterday when my carb was given a little help. Check the power valve(if equipped), could be blown, I dont know a whole lot but basic jetting, but mine would make you cry if you were next to it for a few seconds, now its almost perfect

The power valve is located about the throttle linkage mess on the drivers side of the carb. Turn it in all the way then back out about 2 turns( more or less if necessary). If not check to see if any throttle plates or anything are sticking. I have also heard that if the fuel pump pressure could be too high could make the carburetor run rich. Once done, spray your carb with some carb cleaner just incase.

wild70stang said:

The power valve is located about the throttle linkage mess on the drivers side of the carb. Turn it in all the way then back out about 2 turns( more or less if necessary).

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SHHHHHHHH, the power valve is in the metering block(s)

I set the mixture screws with a vacuum gage. Turn them in lightly to bottom, then back out 1 1/2 turns as a starting point. Then with the vac gage connectewd, turn each one, one at a time to get the highest vacuum reading. Go back and forth until you get the smoothest idle with the highest vacuum.

Rob

Mine was doing this and I found the floats way to high causing it to flood a bit. Acted just as yours is, ran good, bad milage, idled so-so.

Autolite carb correct?
Did those have a powervalve in the metering block like a Holley? I can't recall, too many carbs over the years.
It sounds to me like it's time for a full rebuild... or a minimum of a float level adjustment. I'd be willing to bet running that rich you either have a bad float that's sinking, or, your float level is too high making it run too rich. A good rebuild kit will have all the adjustments explained in a step by step manner.

iskwezm said:

SHHHHHHHH, the power valve is in the metering block(s)

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I forgot the name of the dam screw so sue me. There is a third screw that regulates total idle mixture that is located on the drivers side of the carb, which is what I was talking about originally. I know what I am talking about, just dont know the correct terms for each of the 5 million parts that make an engine work.

I'm assuming you're dealing with idle only, right? That is, it doesn't sound like you're opening the throttle blades at all during these tuning sessions. So yeah, the idle mixture screws are the starting point. I set them with a vacuum gauge, as one other poster mentioned.

But it sounds like idle mixture screw adjustment is not helping your problem. A rebuild I suppose is never a bad idea. It could be a blown power valve is causing your problem, and a rebuild will fix that.

But there is something else that might help, that I learned from the current Car Craft magazine in a story about tuning Holley Dominator carbs for the street. These carbs are known for a fat idle, and you have to lean it out for street use. The way they did it was two steps. First, they used a piece of wire to partially plug up the idle feed restrictor in the metering block. Second, they went up a few sizes on the idle air bleed. In other words, less fuel, more air.

I have no idea if a 4100 has these same features, but I'll bet it has similar circuits somewhere. So go to the Barnes & Noble or whatever and check out this CC story, p. 40 to be exact, and see if it's any help.

Final two cents: you should NOT drive this car much or at all until you fix this problem. An engine running so overrich that it sets off smoke alarms will quickly wash down the cylinder bores, the metal-to-metal contact between the rings and the bores will polish the bores smooth, and you'll have a nasty oil burner.

could be a blown power valve. it should be on the front metering block like a holley. or it could be that the accelerator pump is activating while at idle, possibly caused by the thottle blades being opened too far or the accel pump cam needs adjustment. other things it could be are: dirt or gummy gas varnish in the idle mixture screw. a stuck needle and seat. dirt in any of the internal passages, or a stuck float.

On my Edelbrock I had the same problem with turning the idle mixture screws in all the way and the car kept running. That basicall meant that the car was still getting fuel from somewhere. Checked metering rods first, butterflies, then tracked it down to a vacuum leak under the front of the carb that was allowing fuel to be pulled passed the idle curcuit and into the manifold.

The problem may not be the same as yours in the details, but it is basically the same in the sense that fuel is not following the proper paths through the carb meaning either a vacuum leak or a seal has given in somewhere.

wild70stang said:

I forgot the name of the dam screw so sue me. There is a third screw that regulates total idle mixture that is located on the drivers side of the carb, which is what I was talking about originally. I know what I am talking about, just dont know the correct terms for each of the 5 million parts that make an engine work.

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http://www.bob2000.com/carb.htm


You're welcome