<VV> Re: carb needles and pumps

[GYoungwolf@aol.com]

Some secondary carbs use accelerator pump cups. The easy way to tell is to 
check for a pump discharge hole -- secondaries only have one (unlike the two on 
the primaries). If there is a hole, there will also be a passage between the 
accelerator pump well and the discharge needle hole and you can use a cup. No 
hole means no passage, and thus you should not use a cup as it can force fuel 
out around the bowl gasket. I think that only a few very late 140 engines came 
with secondary carbs without squirters. I find only about 1 in 20 cores 
without them. (If you have some, they can be converted with a little drilling.) 
Secondaries do not have an enrichment needle (although I often find some in cores 
as some had the holes partially drilled for whatever cost cutting reason...and 
some rebuilders were not all that careful.....). FWIW, I also find some 
A.I.R. carbs with operational enrichment circuits. The accelerator pumps (with or 
without cups) are required in all carbs as they are an integral part of the 
carb operating action. The pump discharge needles are simply seals until they are 
forced up by fuel pumped by the accelerator pumps. The enrichment needles are 
operated via a pressure differential at around 50-60 mph under load or at 
wide open throttle. (If you want to get fancy, you can change when they operate 
by changing the weight of the needles). They open another jet (.033-.044") from 
the bowl to the venturi well. GM had a scheme to balance the size of these 
jets to the engine, transmission, main jet, and idle emulsion tube sizes, but 
most carbs have been bastardized over the years (and are the bane of a good 
rebuilder trying to match them up again :-).
The Carbmeister
Should the secondary carbs, on a late '65, have the power enrichment needle?
If so, where are they located?  In all the  breakdown diagrams, they appear
to be in the inner accelerator pump return spring.  There's nothing in mine
except the spring.

Should secondaries have the cups removed from the accelerator pump as stated
in Clark's?  How would it pump then?

What makes the pump discharge needle work, when all it is, is a piece of
brass with a point, sitting in a hole?