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Autolite 4100 carburetor won't idle smooth and lost vacuum


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Hi guys. I have a 1965 thunderbird 390 restoring to original including replacing the 650 Holley with the original 4100 Autolite carb.  I rebuilt the 4100  100% using a kit, but it will not idle smoothly.  seems to run ok on the primary and secondary barrels, and the accelerator pump, secondary actuator, and choke are fine but it will not idle smoothly.  turning the idle mixture screws in and out all the way does nothing,  at idle fuel drips from the primary and secondary venturis onto the throttle plates making an unnatural spitting sound.  I know that's not right.   all I have read says that the idle circuit is not functioning,  I have cleaned out all the hidden passages and orfices in the idle circuits 3 times and can't get it to idle,  the vacuum is down to 19 inches,  should be 24 inches,  so I know there is a leak somewhere but CANNOT find it.  I sprayed WD40 around the base of the carb no leaks were found.  Any more ideas ?   I have tried all the usual tricks 3 times, still can't get it to idle. !!   thanks in advance for your wisdom. 

Edited by andy2175m4 (see edit history)
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Thats typically caused by the float not being clipped into place by that little wire gizmo, it clips around the float shaft and latches against the needle & seat.  Without it being clipped in place the entire float assembly rises up and fuel dribbles into the engine thru the booster.  When it clips in it is a very positive latch, probably hear it snap in place.

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I figured it out,  the primary throttle plates were installed backwards,  and not closing all the way,  and the main/secondary jets were swapped, so I fixed those two and now it runs like a champ,  and yes the float clips are important and they are working properly 

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5 hours ago, andy2175m4 said:

and the main/secondary jets were swapped

I used to pull that dirty trick with Carter AFB carburetors, most notably on a 1965 Chris Craft boat I restored which had a solid lifter 327 Chevy Chris Craft conversion engine in it.  It didn't want to take the throttle because I swapped the primary and secondary jets.  The secondary circuit was supposed to have large jets with stepped metering rods hanging in them.  Hanging those metering rods in the tiny primary jets caused the candles to go out because the metering rods totally closed off the jets and the fuel stopped flowing...

Edited by Str8-8-Dave (see edit history)
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