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Yeah, you're
right about the cowl. Besides, the manifold was not what I thought it was -
turned out to be a "log ram". Different animal altogether.
I'll test the
cowl a little more scientifically this weekend but here's what it does: When the
engine is off the door is open. As soon as you start it, the door closes and
remains closed. Once in a great while the door will open a bit when I stand on
it in fourth gear at low speed (my guess is that it's creating a extra low drop
in manifold vacuum) but not always. When you stab the throttle once in a while
the door will move a wee bit but almost never opens - not even a 1/4 inch.
Basically, it's just not working. There is also an electrical component to the
entire assembly - I don't know what the function is, but perhaps it's something
as simple as a disconnected wire. Who knows...
Craig
Woe Woe Woe,don't you dare take the cowl
induction hood off.I don't have one but the ones I'v seen open when the engine
is turned off.This tells me its manifold vacuum.See if you have vacuum right
at the door on the hood when at idle.Does it open when unpluged at
door?No?mech.problem,Yes?vacuum problem or secondaries are not opening?But
don't loose the cool,unique and rare option.
----- Original Message -----
Sent: Thursday, September 05, 2002 1:15
PM
Subject: RE: [Chevelle-List] Vacuum
problem?
Dale,
I should have
mentioned that the cowl is closed all the time and won't open when you punch
it. However, a buddy of mine mentioned to me last night that he thought the
cowl induction ran off ported vacuum not manifold vacuum. I haven't looked
into it far enough yet to sort it out but I suppose that is possible,
too.
It may become
a moot point as I just found an old Edelbrock cross ram manifold for a BBC
that mounts a pair of 4 barrels! It may not run worth a crap but it sure
would LOOK cool! I may even sacrifice an operating cowl induction to mount
that puppy under the hood.
Craig
Craig,
I assumed the cowl vent was open
all the time and not shut all the time; although the poster didn't
specify which. May be a bad assumption on my part (?)
Being open all the time would be an indication of no
manifold vacuum at the valve to close it under normal driving conditions
or when at idle. I don't know the vacuum hose routing from the flapper
valve but the line may be pinched or the valve is bad. Since you
would normally have 14-18 inches of vacuum at idle, that should be more
than enough to close the flapper valve. I would assume it opens at
somewhere between 5 and 10 inches of vacuum when you nail
it.
Whether this has anything to do with the
carb secondaries I would doubt since they're operated at the carb via the
spring - unless the carb has recently been rebuilt and not put back
together properly but I think they're be a sucking sound you could
definitely hear. Unless you can feel when the secondaries open under
a load at WOT, I don't think you'll see them open just winging the engine
while you're watching it. And I sure hope you're not testing it like
two guys I read about that got stopped in a car with the hood off.
One guy was sitting in the engine compartment to verify the secondaries
were opening while the driver was hauling a$$ down the
road!
Dale,
that's what I've always thought but I think the cowl induction system
works manifold vacuum drops - as in when the throttle is punched wide
open. My understanding is that vacuum is what keeps the cowl closed -
that's why is snaps open when you turn off the motor. I am not a
mechanic and could be wrong about all this - but the logic of the system
seems to indicate this is how it should work.
Craig
E
I wouldn't think so it'd be possible
to generate too much vacuum. Both my cars (396 and 327) pull
about 17/18 at warm idle, 15/16 cruising at steady throttle and jumps
to 24/25 range when decelerating.
You problems sound like lack of
vacuum - bleeding off somewhere.
Dale McIntosh
ACES #1709/TC #92
Gold
67 SS/67
Elky
http://www.dalesplace.com
http://www.team67.com
http://www.midwestchevelles.com
Is it possible to generate
too much manifold vacuum and, if so, how does one diagnose the
problem and remedy??? My cowl induction has stopped working and my
vacuum secondaries appear to be malfunctioning. I'm wondering if the
problems are related...
CAE
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