Cap'n Bob and other listers following this thread,
My original point of technical disagreement on this thread was that there
were no check valve balls in the acc.pump circuit that I had found and this
is what I said
"The original point was about the pump jet circuit having a ball check
relief valve and the fact is it doesn't as far as I know and no-one has
demonstrated that it has"
This point arose from a question about how can the acc. pump jet act as a
high speed jet in that surely it couldn't and must have a check valve.
Well I now know different at least as far as the check valve goes! And I
have demonstrated to myself that it has, though Cap'n Bob deserves due credit
for persisting with me.
However, Cap'n Bob also said "unscrew the fittings on the top of the carb and
find out what's "inside"; don't lose the tiny "balls" and this is not
strictly accurate because the balls sit under a brass 'spacer rod' (looks a
lot like an SU float jet but round at both ends) and this rod in turn sits
under a brass capping screw. So, the balls aren't easily lost and this part
of the carb acc. pump jet circuit isn't calibrateable. Although Cap'n Bob
says "unscrew the fittings on the top of the carb and find out what's
"inside"; don't lose the tiny "balls" should lead to finding them I had to
do this twice because the brass rod conceals them.
One of the interesting things about the balls and brass rod is what happens
if they are missing or worn and I guess you get fuel siphoning out of the
float bowl all the time - not something that you would necessarily notice in
driving the car or even dyno tuning the engine because the other calibration
would be such it compensated for a constant stream of fuel from an unchecked
pump jet. However, with the engine switched off there might well be a steady
drip of fuel until the float bowl was empty - *** Frank, could this be the
answer to that problem you had a while back? ***.
Back to the original question: Doesn't the acc.pump jet have a check valve
that prevents fuel streaming from it at high rpm and acting as a high speed
jet? YES and NO. Yes it has a check valve but no it doesn't prevent it
acting as a high speed jet. Having found the balls (one each side) it is
hard to see how the acc.pump jet can stream fuel at high rpm but Weber (and
others) says it does and they designed and built the carb. Having pored over
the fuel galleries etc I can only guess that once the fuel downstream off the
acc.pump jet has streamed off at high rpm the vacuum in the jet itself and
the gallery (admittedly not a particularly long run) must be such that its
strength is greater (at high rpm don't ask me why not high manifold vacuum)
to lift the rod and ball sufficiently but not all the way off the seat to let
a small amount of fuel to continue to stream.
So, I admit I am half wrong :-( but it was interesting to find out why :-}
Daniel1312
In a message dated 10/08/01 14:27:57 Pacific Daylight Time,
Daniel1312@aol.com writes:
<< nothing drops out when
it is off whether the carb or the cover is shaken or not. There is a ball
bearing in the float needle valve but it can't and doesn't come out. In
fact
it doesn't come out AFAIK even when the float assembly is removed.
SO
No balls drop out and no balls in the acc pump jet circuit. >>
|