----- 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
