DeTomaso Mailing List: May 1997, Message #215
     



From: MikeLDrew@aol.com

Subject: Weber Redux

Date: Thu, 8 May 1997 04:32:40 -0400 (EDT)



Capt Mike Drew,

etc. etc. etc.



Hello all,



Here's one more note on Webers, not from Capt Sensible (which I'm clearly

not) nor from Capt Sensitive (which I'm not either, I just forgot to put a

smiley face on that one post, so here it is now: :>)  ), but rather from Jack

DeRyke in an article which ran in my 1994 PCNC newsletter (and which may yet

find its way into the POCA newsletter someday.)



And now, Jack:





I have harped on this theme before, but here we are again:  complex

mechanisms must be understood as systems,  rather than (to paraphrase an

aircraft saying), as "a collection of loosely-associated parts flying in

close formation"...Recently, I had occasion to speak with a gentleman who had

experienced that most terrifying of problems for exotic-car owners-an engine

fire!  These are particularly bad in mid- or rear-engined cars, 'cause you

may not notice it right away, which allows the blaze to really get going

big-time!



It involved a Pantera that had a nicely-done 48 IDA Weber conversion

installed.  The owner had massaged the decklid to clear the rear carbs, the

manifold was polished to perfection and he had even sprung for

dynomometer-testing to get the jetting sorted out.  Then, he hung a custom

aftermarket air cleaner on the engine and began putting miles on his

creation.  He'd done everything correctly, right up to that last move.  See,

quadruple Weber carb setups use intake manifolds that are known as

"individual-runner" types; that is, each cylinder has its own carburetor

barrel not connected to any of the other carb barrels.  When a piston

descends in the cylinder and the intake valve opens, a strong vacuum is

created which pulls air and gasoline down into the cylinder.  Then, the valve

closes, and the flowing air and fuel slam into the back side of the

now-closed valve.  This reverses the air and fuel direction back up the

intake pipe toward the carb.



These vacuum-driven air pulses are incredibly strong, but in a normal

"Detroit"-type intake manifold, there is a fairly large chamber just under

the carb which is known as a "plenum".  This chamber connects all the intake

passages together, which acts as a big damper on these pulses.

Individual-runner (I.R.) intake systems do not have plenums, so these strong

pulses of air/fuel go right back through the carb and out the air-horn on

top.  A peculiarity of carburetors is, they will feed gasoline regardless of

which way the air is flowing.  The result is a condition known as

"stand-off", where when tuning an I.R.-type fuel system with no air cleaner,

a visible cloud of gasoline vapor hangs just above the carburetor air horns.



"Okay, okay", you say, "So what?  I know all about fuel inversion and

'stand-off'.  What's the big deal?"  Just this:  the car owner had selected a

foam-type air cleaner that really looked nice, fit well, and efficiently

cleaned the incoming air.  And soaked up that stand-off gasoline like a

sponge (which it was, of course!)  Another well-known peculiarity of Weber

set-ups is, they tend to pop or spit back a bit, especially when the engine

is cold.  Let's be accurate here:  a spit-back is really a backfire through

the carbs.  And this time, the burst of (back) fire out the air horn touched

off the gas-soaked foam air cleaner, which then lit off all the combustibles

within a foot of the carb before the driver noticed the bonfire blazing

merrily behind him, the engine having started running at idle after the

momentary backfire.



Well, all ended well, sort of.  This particular car owner was one of the

minority of Pantera owners that carries a good fire extinguisher in the car,

and knew how to use it.  The fire was put out quickly, with only minimal

damage to the engine, paint and bodywork (not counting the damage to the

owner's heart and stomach lining!).  He was really lucky; Weber fires usually

result in the small auxiliary venturies melting since they are made of

pot-metal.  The molten metal runs down the intake and into the motor.  When

that piston comes back up, presto-you've got a smashed piston or a bent rod!

The pretty custom foam air cleaner?  It wound up far out in a vacant lot

alongside the scene of the fire, after things cooled off enough to allow it

to be removed!  A plain-vanilla paper air cleaner went on the Webers the next

weekend.  Paper air cleaners do not soak up blown-back gas, although it's

still present inside the air cleaner body.  Now when a "pop" occurs, there is

far less chance of an actual blaze starting (on that car, anyway!)



And lest you think that this is an isolated incident, recall the excitement

in the pits at Las Vegas a couple of years ago, when the Adlers' Whiplash

Group 5 Pantera decided to ignite its air cleaners!  Fortunately, spectators

alerted the Adlers to the problem, and they were able to get the fire

extinguished almost immediately, resulting in no damage to anything other

than the filter.



The second disaster happened to me (yes, Virginia, even Shadetree Mechanics

can screw up now and then!)  My problem revolved around the addition of a

fuel filter between the fuel pump and the carburetor, specifically one of

those small glass ones that let you see fuel flowing, which can be very handy

when troubleshooting.  These filters are made of a thick glass tube, two

chrome-plated brass ends with seals, a plastic filter inside and a threaded

steel rod which holds everything together.



Problem is, that rod isn't hollow but solid, so in order for fuel to be able

to flow around it on its way in and out, the ends of the rod are cut flat

about halfway through.  This severely reduces the ability of the rod to carry

any torque when the filter is assembled.  The first sign of a problem was

when my wife started our Pantera and backed it out of the garage on our way

to a club meeting, shortly after I had installed it.  Due to the arrangement

of our garage.  I do not own an automatic garage-door opener, so I was

waiting to close up when I noticed a very large pool of raw gas appear under

the car as Judy backed it out.



When I frantically motioned to Judy, she shut down the engine, and we pushed

the Pantera back into the garage by hand.  We drove to our meeting in our

baby Pantera (a.k.a. Pontiac Fiero), leaving my two sons to mop up the

spilled gas and close up the garage.  Later, I found the threaded brass end

of the brand-new fuel filter had stripped out, maybe during installation,

maybe as a manufacturer's defect, which allowed about half of the gas pumped

to the carb to spray out onto the running engine!  I shudder to think what

might have been on the freeway with a hot exhaust and the volume of has that

was leaking.  You did realize that, if you have a car fire that seems to be

burning pretty well, the California Highway Patrol (and most other

law-enforcement agencies, probably) will physically restrain you from

personally putting it out, even if you have a fire extinguisher in hand.



You will wait for the "professional fireman" to show up.  Their rationale is,

you might get hurt and sue the City, County, State and/or the CHP while "any

car can be replaced."  This ruling obviously was not dreamed up by a car

enthusiast!  Imagine being forced to watch your beloved Pantera possibly burn

to the ground from a "safe distance,"  while being held in place by an armed,

unsympathetic cop!  I believe there is more danger of a heart attack or

stroke from such a circumstance than injury from a burn or explosion of the

gas tank!  However, the California Legislature neglected to ask my opinion

when they handed down this little gem.



Bottom line:  don't install anything on your car having to do with gasoline

until you totally understand how it was built and what it's supposed to do.

Then, put it on and test the heck out of it before you drive away!  And

always, always carry a good fire extinguisher with you.  They're not just for

open-track racing!  I recommend at least a 2 1/2 lb or (ideally) a 5 lb Halon

type, ozone layer be damned!  I've cleaned up the damage done by those

corrosive powder-type extinguishers before; it exceeded the damage done by

the fire!  Halon extinguishers are hard to find in California; you might need

to shop out-of-state for one.  Mount the extinguisher so it's visible as you

enter the car, and make a habit of looking at its pressure gauge each time

you climb in the car, before you reach for the ignition switch.  The heart

you save might be valuable to you someday!



(Mike Speaks Again:  Having experienced three under-dash electrical fires and

one massive fireball-through-the-air-cleaner, I have a healthy respect for

the dangers of fire.  Besides carrying a Halon extinguisher wedged between

the seat and the center console, I always made a practice of unlocking my

rear deck lid before unlocking the door, and locking it again upon leaving

the car.  Why?  Well, imagine driving down the road and discovering smoke

pouring from your engine compartment.  You stop, jump out of the car with

extinguisher in hand, only to find that your deck lid is locked and you can't

get to the fire.  Now, you have to go back inside the car and fetch your

keys, then try to remember if the teeth face UP to unlock or DOWN to unlock

as you fiddle with the damn lock to get the lid open so you can start

fighting the fire.  By this time, the only thing left of your car might be

the trunk lock!  By keeping rigid habit patterns in this matter, I not only

ensure that I can get to the engine in the bare minimum time, I also ensure

that I never leave the car parked with the trunk unlocked.  Think about

it...)



(And Dennis, if you now start calling me Captain Rigid, I'm gonna clobber

ya!)  :>)



Mike