Doug,
RE:
> Brian, -when you said: " When you run the idle speed screw in past where is
> is designed to be, you start using intermediate speed fuel for idling. If
> you ease into the throttle it goes lean for a moment (no intermediate speed
> fuel) and pops. " I THINK you meant idle MIXTURE screw didn't you ? That
> would make sense to me anyway
What I'm talking about is what Tom said:
The transition from idle to main jet operation requires some overlap of
the systems.
And:
I have found that, if the fuel level is correct and you still
have a problem, drilling the idle tubes just a bit will cure the problem.
The transition from idle to main jet is the job of the intermediate fuel
circuit.
This is how I understand that it works (list, keep me honest here)
At idle speed the fuel enters the air stream through the the idle fuel
passage at or just below the edge of the butterfly valve. The amount of
fuel is controlled by the hole in the idle tube, which has little effect
because of the small amount of flow, and idle mixture adjustment screw.
As the butterfly valve starts to open, holes which are just above
the idle port are exposed to manifold vacuum and fuel starts to flow
into the air stream compensating for the additional air flow.
(At idle, none of these holes should be exposed to vacuum.)
As the first hole is exposed to vacuum and fuel starts to flow, the
restriction/hole/jet in the idle tubes (thanks Tom) begin to control
fuel flow/mixture.
By the way, I wouldn't touch the float level until after the idle problem
is cured.
Assuming the current idle SPEED SCREW setting has the butterfly exposing
one or more of the transition/intermediate ports, what you need to do is
bleed more air past the butterfly so that it can be closed back to it's
design position.
This gets us to:
> Then you stated: " You can close the butterfly and still get enough air by
> drilling a new/larger hole in the butterfly. "
>
> - Any idea for me how BIG a hole would do it ?
This is really the black art part of this Doug. I hope someone on the list
can give you some better ideas than mine, but this is what I would do:
Assumption: There is already a hole in the butterfly...
1) Very careful measure the "Before" position of the Butterfly (feeler gages?).
2) Drill a 1/8" hole in the plate and test it.
Note: The idea here is to allow the hole(s) to be soldered shut if you go too
far.
3) Examine & measure the new position of the butterfly.
4) If more air is needed to close the butterfly to where it should be, add a
second 1/8" hole and test.
If more air is still needed, I would calculate the area of the OEM hole,
add .025, the area of two 1/8" holes, and drill out the OEM hole to this new
area and repeat the test.
If you go too big on the OEM hole, you can solder one or both 1/8' holes shut.
While you are doing this Doug, keep track of how far out the idle mixture
screw is and make sure you can always use it to go too rich. I use a propane
torch, to richen the mixture, when I'm not sure where I'm at.
If you cannot make it too rich with the idle mixture screw or it is way too
far out you will need to drill out the idle tubes until you regain control
of the idle mixture.
If you have the instruction sheet from an overhaul kit it may give you
the initial starting point for butterfly opening.
That's all I can type for now Doug.
Call me and I'll try to do a better job of explaining, (530) 647-0694.
If my wife answers tell her you're a Bonneville racer.
Bryan Savage
PS to list: I don't know where "Land Speed Racer" after my name came from,
I'm just a spectator these days.
PS #2 to List: Howard is getting better slowly. His engine man pulled out
so he's looking for a motor. He will be a Bonneville for a few
days this year. At least for the 2 Club party.
He's not on the list now, but I'd appreciate it if some of
you folks would send him a note and say Hi.
Howard Nafzger nafzger@vtc.net
Thanks to all...
Bryan
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