<VV> Re: LM carbs

[Tony Underwood]

At 06:47 hours 05/02/2006, Rad Davis wrote:
>I've been through this exact scenario with my van.  It took me a 
>year or so to figure out why the off-idle behavior of the engine was 
>weak and unpredictable.
>
>It turned out that I had a '65 carb on one side, and a '66-67 
>non-smog carb on the other.  This oddball has the lump where the 
>idle bleed screw would be installed, but the hole is undrilled in 
>the casting.  The idle transition circuits are different between 
>these.  The newer model transition circuit cuts out sooner.  I 
>suspect that it goes with a venturi cluster with a smaller bypass 
>orifice to move the cut-in point of the main system down in the 
>operating range of the engine.
>
>The van ran OK with this arrangement, but it was difficult to 
>feather the clutch in for soft starts with a step function in power 
>output off idle.
>
>As for smog carbs running leaner, there's an idle air bleed 
>adjustment on all true smog carbs.  you can adjust them to be as 
>lean or rich before main jet cut-in as you like.  From the factory, 
>theyr'e adjusted to run lean because that was what CARB and EPA 
>wanted.  It is useful to remember that the brass screw inside the 
>air horn is an air bleed, not a fuel adjustment, so out is a leaner mixture.



My issues with the late-late carbs is that oft times that air bleed 
screw has been untouched for too long and it's stuck tight, strip 
metal off the slot trying to turn it.   I have several of these carbs 
that I parted out, VAB screw stuck solid and immovable.   A couple 
others that were stuck, but also in better shape otherwise, got 
"fixed" by just dobbing the JB Weld over the slot vents in the air 
bleed, plugged, forgot about it and all was well.   Idle mixture then 
adjusted like any other carb, seemed to run better.   I was happy.

If the screw still moves, then you can work with it...  around here 
it seems that half of them simply won't move anymore.    They got 
plugged.   ;)


tony..