<VV> Hard to Start...

[Tony Underwood]

At 08:18 hours 10/12/2006, Mike Stillwell wrote:

>  Hmmm, maybe we're on to something. I like to run them
>about 2 full turns out. If you get bored, try that set
>up (Secondaries all the way in, Primaries 2 turns
>out).


This allows the idle bleed air to come from the primaries only, IF 
you also backed off the idle speed adjust screw on the secondaries so 
they don't try to draw any more fuel than necessary from the 
idle/off-idle circuits.   Then, if you tighten the mixture screws to 
kill the bleed air on the secondaries, your primary carb mixture 
screws will function normally, as per "the book".

Been there done that a couple times.


> >   oddly enough Mike, I have noticed that the car
> > idles smoother
> >   when I turn the idle mix screw all the way in and
> > then just barely
> >   open ( @ 1/4 turn) on all four carbs !
> >



This is what happens when you run four carbs with idle 
circuits.    Doing it this way, you'll likely need to adjust all four 
for the best idle, which gets to be twitchy what with also having to 
juggle the idle speed screws on FOUR carbs instead of just two, along 
with their corresponding idle mixture screws... each of which then 
only requires half as much air through the mixture circuits because 
you have FOUR air bleeds instead of just two.

It's important to remember that the mixture screw is an AIR bleed, 
not a fuel feed.   Tighten it, richer idle mixture, (depending on 
throttle opening) loosen it, leaner mixture.  It's a combination 
adjustment... to a point.    If the throttle is completely closed, so 
that no air passes through the carb venturi, the air bleed 
effectively becomes pretty much moot.

To get to what "the book" states, you'd have to completely close (as 
in back off and/or remove the idle adjust screws) the throttles on 
the secondary carbs and tighten the air bleed screws all the way down 
so as to shut the secondary air bleeds off entirely.   Then, ignore 
the secondary carbs, adjust only the primary mixture screws for 
smoothest idle and the primary idle adjust screws for the correct 
idle speed.   The small amount of fuel which will find its way 
through the secondary carbs from the idle circuits will be 
insignificant when it's done up this way, and the idle mixture screws 
on the primaries can compensate for it.    You should be able to get 
a smooth idle and a steady idle speed this way.


These are the issues you'll get when you run primary carbs as secondaries.



tony..