[AMC-List] Re; AMC Spirit questions - TOM

["John Elle" <johnelle@xxxxxxxxx>]

From: Tom Jennings <tomj@xxxxxxx>
SNIP
On Fri, 20 Oct 2006, John Elle wrote:
. I prefer a Carter AVS or AFB my self
*      between 350 and 400 cfm
*       
John, all your comments are good. I have a question on yr carb
ideas above.
 
What Carter AFx carb is 350 - 400 cfm?
SNIP
 
Tom, 
Keeping in mind that carburetors are not getting any newer a lot of
carburetor selections are getting older and harder to find but if you
want to use one bad enough they are still out there. My disdain for
Holley's is high enough 
(SNIP 
The Holley 390 (but Holleys seem to need constant fiddling for reliable
treet use not their intended use)
 SNIP
 that I absolutely refuse to use one and will go through multiple
hurtles to find the Carter that I want and get it adjusted correctly.
'Cause I know it will work right almost for ever with out any further
futzing with it. 
 
SNIP
There doesn't seem to be many "performance" carbs (I use that
word loosely) in the under-500cfm range. The Holley 390
But the smallest AFB I know of is 500cfm, and the AVS, isn't
that old, unavailable, and 600cfm-ish?
SNIP
 
The Carter 9000 series performance carburetors available some where
around the middle 70's and into the 80's were configured so that the
part number  corresponded to the flow rating of the carburetor. I used a
9425 on a modified 225 slant 6 with excellent results and drove it for
far more years than I like to remember but it was dead reliable and
quick and would get 20 mpg+ at steady freeway speeds. This pulling a
Belvedere 2 drht. Data I have show  a 9400 and four versions of a 9500
were manufactured.  Finding one might take a bit but for me worth the
effort. The AFB uses a counterweighted air valve just above the
secondary throttle plates that will not open unless the demand for
additional air flow is generated by the engine. Un like a Holley that
will just open and bog the engine down. Thus if an engine (such as a
smallish 6 or V8 uses one, until it is wound up to the point where it
needs the additional air flow the secondary remains blocked and will be
allowed to open gradually. The AVS used a spring loaded secondary much
in the same way but were mostly manufactured for specific engines and
were rather small. They quite possibly would be found on small Chrysler
V8's for the most part but may be found on some dual quad applications. 
 
SNIP
) and the Webers are about it;
SNIP
 
I never messed with a Weber, so I can not comment on it. 
SNIP
 the BBDs are fine too except for the limited adjustability.
SNIP
 
Actually I find just the opposite to be true. There is a fair amount of
interchangeability with the metering rods with the AFB if I remember
correctly. But for the most part the adjustability is used to get them
to operate correctly in the first place and then forget about them. 
 
PS: Here's a small chart of rpm vs. engine CFM for 258 ci,
assuming 80% VE (I hope it's better than that!):
 
The infamous Smokey advocated treating an engine like an air pump, thus
at 100% it would be 
RPM    CFM           CFM
1000    60               75
1500    90
2000    119           149 
2500    149      <---
3000    179            224
3500    209
4000    239             299 
4500    269
5000    299      <---373  
5500    328
6000    358             447
 
So a 9400 would fit in there nicely but a 9500 would work and with the
secondary air valve compensating for it a Carter would be quite
versatile 'specially if you are running a little cam. My choice for cam
is a Horse Power Cam though and a wee bit of rpm dialed in. Not
something sometimes referred to as an  RV Cam.  
SNIP
The two arrows are of course likely cruise RPM and max RPM
(stock small AMC, 70's). 2500 is perfect for the little YF,
which is sucked dry at speed
SNIP
Which is why these things fall flat on their face over 3 grand stock,
they are grossly under carbureted and under cammed.  
 
SNIP
 Dual YFs would be nice! :-)
SNIP
 
They sure would, if you could find a manifold for them, multiple carbs
are great oooo aaahhh factor too!
 
Now as to new, Edelbrock seems to be the only source for what used to be
Carter carburetors 
http://www.edelbrock.com/automotive/index.html
Edelbrock Performer Series Carbs
500 cfm Carburetors
500 cfm, square-flange, electric choke ....#1403* 
500 cfm, square-flange, manual choke ....#1404*
Also Rochester and maybe more and I have not checked to see what they
have in strip kit equivalents but as I have a small selection of tuning
parts for Carter Carburetors  I have not needed to buy anything in a
while. But then again, this still would be my choice for Carbureting an
AMC I6 engine or V8. 
I am not sure if they have anything smaller available but as far as I am
concerned I would install an Edelbrock 500 cfm performer new over any
kind of a Holley 390 anything on a small engine. 
 
As you know, my last I-6 was a fuel injected retrofit which although I
finally got running the way I expected it to run I feel was a very poor
bang for my buck when it was all said and done. Except for one thing. It
had a smog legal paper trail which was in part why I went this route. 
 
The single biggest disappointment was the MMAP sensor was defective and
it never showed up in the diagnostics, the next biggest was the lack of
adjustability (it needs more timing advance and you can not get it) and
one of the last disappointments a blatant misrepresentation of the
benefits in overall performance improvements. 
 
A continuing nagging problem is a poor location for fuel pick up in side
the gasoline tank which has cost me about 5 fuel pumps over the years. 
 
Anyway, hope this answers some of your questions in a fair manner. 
Later. 
John. 
 
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