Hey guys:

I have encountered a strange situation. In the past few months I have overhauled one Holley 2280 and one Carter BBD. Neither would idle once off fast idle as adjusted "normally"... i.e. idle mixture 2-1/2 turns out and idle speed set to spec. The similarities are:

1. They are both spec'd for a 1978 318 V8...don't recall list number from the Holley but the BBD is an 8175S

2. They both have what I call brass idle feed restrictors in the baseplate, located in the passages on each side just above the idle mixture screws.

So, what is the story with those restrictors as I call them? I swapped baseplates on the 2280 with one that did not have those and it idled fine. I have another for the BBD that also lacks those things and I may try that as one last-ditch attempt before I abandon those model carbs forever. Those are not the carburetor a Rochester 2G is, that's for sure.

Nothing different stood out about the Holley, but the BBD has one of those "closed throttle switches" I guess it is called...the one with a metal stop with a wire connected that creates a ground signal for probably the Lean Burn.

I feel like I'm almost on top of this but some further insight about this beast would be great, thanks.

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1966 Chrysler 300 coupe
1968 Plymouth Valiant 100
1969 Dart Custom 273 V8

Watch training film http://imperialclub.org/Repair/Lit/Films/348/ They can be removed or enlarged for more idle flow.

Brass idle atomizer tube, called low speed jet in picture,sits in a low spot lower than main jet. Crude settles in this low spot. The tubes are long and get too close to crude. Vacuum from idle sucks up both fuel and some crude,eventually blocking low speed jet. Jet size is .0295 decimal 75 mm metric , that size drill bit or welders tip cleaners is only effective way too clean tube.

Tip cleaner sample http://www.weldingaccessoriesindia.com/ ... aners.html

Thanks, you guys are awesome. Don't know how they expected it to idle like that unless the Lean Burn advanced the timing way up at idle. I have another base that should work fine and I'll try that.

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1966 Chrysler 300 coupe
1968 Plymouth Valiant 100
1969 Dart Custom 273 V8

I run a 2280 from a 318 on the slant motor in the 83 D150, don't know if it has the restrictors that you mention, however

I have always adjusted the idle mixture screws for maximum manifold vacuum at idle.

as you adjust the idle screws you will need to adjust the idle speed to get the RPM's back to the target
and if you run vacuum advance, plug the hose to the carb while in the set up mode

IIRC my set up runs best at about 3 1/4 turns out. I have an wide band AF gauge and get low 14's at warm idle.

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

https://app.box.com/s/15dt5qav20ccxcnzp9e4 On page 7 Idle by-pass assist, see if your carb has this , some 318 carbs had this extra port. If open try blocking it.

red line is by-pass

8175 1978 federal emissions ,manual trans. Used venturi screw 101-639 same as used in 1978 slant six trucks for one year only .Most slants used 101-569, 318 used several different numbers. Inside that screw are two restrications , Just under screw driver slot is air bleed .059 number 53 drill. Just under cross over holes is economizer idle restrication also .059.Lost old notes but guess that 639 has bigger air bleed .063 and or different economizer -.063 or .055. or the same .059. The screws are stamped with the last 3 numbers,will need good mag glass.If you have extra screws, use the ones that work best.