> > Unless a HIF is quite a bit different than the earlier models,
> the piston
> > gets it's vacuum signal directly from the venturi, which should
> be quite a
> > bit more than the vacuum between the piston and the throttle plate.
>
> I thought that that vacuum, was what sucked the fuel up, but that the
> backwards facing ports in the bottom of the piston were past the
> bridge and in the area between the bridge (venturi) and the throttle
> plate.
Could be, on a HIF. On H and HS models the ports are in the bottom of the
piston, and overlap the trailing edge of the bridge, which I believe means
they still see at least partially the venturi-amplified vacuum signal. I
could be wrong ...
> > Have you tried heavier oil in the dashpot ? That's it's
> function, to richen
> > the mixture when you open the throttle suddenly.
>
> It slows down the piston movement and I'm running 85/140 in the
> dashpot. I've got some stuff that is heavier, but then the piston
> drops very slowly too.
There should be a one-way valve in the plunger, that allows the piston to
fall quicker than it rises. But if you're going heavier than 140, it
probably does fall pretty slow. Is that a bad thing ? Seems like all it
would do is cause the mixture to go lean when you close the throttle, which
might not be all bad.
> A heavier spring (as I understand it) increases
> the velocity of the air through the venturi, increasing the vacuum to
> the jet and also "stretches out" the profile of the needle so that at
> the same airflow, you are "lower" or thicker on the needle.
Sounds good to me. Also limits flow to some extent, by raising the pressure
drop across the venturi.
> I'd like it to move easily at low loads, but the piston hits full
> movement way before I've got full airflow through it.
That sounds to me like you should be looking for a -8 carb!
> I also want to
> keep the mixture as lean as practical at low loads as it seems to make
> a 20-30% in fuel economy.
Which was the thought behind a more tapered needle ... you can make it
richer at higher flow rates while keeping it lean at lower flows.
> I suspect that in my zeal to understand everything that is
> happening, I might also be a bit more vocal about discussing it. I
> also have enough vanity to think that enough people are interested.
I am ... guess now is the time for others to say they'd like to see this
discussion taken elsewhere.
> I know that there are other folks besides you and I with supercharged
> british Iron. Would there be enough interest to set up a mailing list
> (probably a yahoo group) for others that share our
> afflic^H^H^H^H^Hinterest?
At least for discussing carbs and needles, the Team.Net Judson list might
not be a bad place. Several folks over there seem to be having mixture
problems as well.
Randall
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