Technical aspects of automobiles

Archive for August, 2009

Mazda MX-6 engine/tranny

I have a 1988 Mazda MX-6 DX (2.2 litre 12-valve EFI engine) with
automatic transmission and air conditioning.

When the car is started in the morning the engine does not idle
properly. About 5 seconds after the car is started, the RPM begins
to fall. When it reaches about 1500 RPM I hear the engine rev and
the RPM jumps up to about 2000 RPM. The RPM then starts falling
again and as soon as it gets to about 1500 RPM it jumps up again to
2000 RPM. This goes on and on until I finally put the car into gear.

Sometimes this unexpected jump in RPM occurs while I’m driving.
Several times while cruising along at a steady speed,
the RPM would suddenly jump up by about 1000 RPM and
it feels like the car has down-shifted.

Does anyone know what the problem could be?

 Phillip Hum                      ** My views do not necessarily **
 Bell-Northern Research           ** reflect the views of BNR.   **
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Re: Integra Front End Howl

 > From: ch…@xrtll.uucp (Chris Baisly)
 > Date: 15 Aug 90 23:58:16 GMT
 > Message-ID: <1990Aug15.235816.26…@xrtll.uucp>
 > Newsgroups:
 > I have notice in the past few days that my 1987 Integra
 > front end howls when I have the steering wheel at one lock
 > or the other (ie full turn).  This occurs in parking lots
 > and such when tight maneouvering is required.
 > I’m not sure if it is a new noise, but I have just started
 > noticing.  It wouldn’t surpise me if it is a normal sound
 > the CV joints make, at least I hope it is.
 > The car has manual steering, and the howl is proportional
 > to speed, so it isn’t a power assist or related problem

sounds like a worn outer cv joint…
good luck


        Steve Kaess at The Black Cat’s Shack (Fidonet 1:109/401)
        Internet:  Steve.Ka…    
        UUCP:      …!uunet!blkcat!417.0!Steve.Kaess

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Re: Disc brakes vs. Brake Drums

>>So that is my question, why are disc brakes
>>used on today’s cars?  Is it because it is easier to work on?  Do they work
>>better?  Why because they clamp/squeeze the rotor?

> Because they cool better.  The friction surface on a drum brake is
> inside, away from the air flow.  On a disc brake it is directly
> exposed to air flow.

  I think it goes deeper than that. Suppose you had the choice between
  drums or discs to stop you in an emergency in they were at the same
  low temperature, which would you use ? Discs I guess. Now if drums
  or discs were at the same temp. then why are the discs better ? In the
  wet the discs will get wet whereas the drums won’t (the friction
  surface I mean). The surface area (apparently) for drums is higher.

  I think the real answer lies in the way the pistons clamp the pads
  onto the discs as against the way this is done in the case of shoes.
  The force available to push the friction material against the brake
  disc is higher than in shoes.

  The ability to stop the car lies in the amount of kinetic energy that
  can be dissapated as heat (or, as in the case of Taxi cabs-sound !)
  before the tyre looses grip on the road source, i.e. the wheel
  `locks up’. So the larger the pad/disc surface area the better.

  On my TVR I’ve fitted some ducting to blow cold air onto the discs
  and I had no fade problems during a road rally th other night. Another
  improvement (the discs are 11 inches in diameter) is to fit four pot
  calipers to even out the push on the disc. The discs can be slotted
  to remove surface sheen and the highest luxury is to run ventilated
  discs with two lots of four pot alloy calipers per disc !!

              John Upham, (Chemical Physics Ph.D)

              University of Sussex, Brighton, UK.



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Re: dual exhaust

In article <3…@rsiatl.UUCP> j…@rsiatl.UUCP (John G. DeArmond) writes:

>r…@prism.gatech.EDU (Richard Catrambone) writes:
>>What are the benefits of installing a dual exhaust
>Dual exhausts don’t buy you anything per se.  Actually in some
>cases, I prefer one large tube.  What does buy you something is
>anything you can do to lower backpressure in the exhaust.  

If the system has low back-pressure, then it is more resonant, and hence
has a tendency to peak on the negative pulse extraction effect at
certain rpm. This peak can be flattened out by diluting it with another
resonant mode by adding a so-called "balance" pipe connecting the two
halves of the dual. Also reduces the back-pressure a bit too. Less used
in racing because racers want to exploit well-placed peaks in response,
less interested in flat flexible power curves.

Chris Malcolm    c…   031 667 1011 x2550
Department of Artificial Intelligence, Edinburgh University
5 Forrest Hill, Edinburgh, EH1 2QL, UK

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Re: tesing for water in gasoline

bes… (Brent H. Besler) writes:

>Well a simple test would be as follows:
>Put some some of the gasoline in a test tube.  Add some ethyl(denatured)
>alcohol.  Mark the level between the two layers.  Shake it up.  If the
>alcohol layer(bottom) increases in volume there is water in the gas.  The
>alcohol extracts the water from the gas layer.  There are test kits that
>probably put a dye that is souble in only the alcohol/water layer to make
>it easier to see.

That works pretty well.  Another old racer’s test is to mix the gas
about half and half with racing grade methanol and then add some
oil (40:1 or so will do).  If there is significant water present,
the oil will separate out from the methanol and make the mixture

I kinda wonder from the description of the symptoms given by the original
poster if maybe they might have contaminated the gasoline with either
diesel oil or kerosene?


John De Armond, WD4OQC  | We can no more blame our loss of freedom on congress
Radiation Systems, Inc. | than we can prostitution on pimps.  Both simply
Atlanta, Ga             | provide broker services for their customers.
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Re: Running high RPMs

ER…@pucc.Princeton.EDU (Eric T. Bergman) writes:

>I have a 1990 Acura Integra.  While it’s not a Mustang, Camarro or a
>Supra   |^)  I like to run it hard sometimes, about 6000 RPMs.  It red-lines
>at 6500 and I never rev it that high. Q: How bad is it/Is it bad to run
>the motor that hard, (it already has 3000 miles on it) ?

About the only thing bad about doing high revs is that  you’ll  probably  be
burning fuel prodigously without any real increase in hp.  This  is  usually
because your maximum power/torque is reached (with  your  engine)  somewhere
around 4500-6000 rpm. As it is, there aren’t any real dangers  from  revving
your motor hard, about the only danger I can see is the stock valve springs.
The standard valve springs may not be stiff enough to  prevent  valve-bounce
at high revs. If a valve  bounces against a piston at high  revs  you  might
end up with a vapourized piston and a hole in the cylinder block.

Normally with a new engine/car, the owners manual gives you a recommendation
about how many kms you should do before you start becoming generous with the
throttle. Stick to their recommendations, but don’t have the engine at  just
a narrow band of revs – vary that over the first few thousand kms. From what
you’ve already mentioned, it sounds as though you’ve run the  engine  in  by
now, so there shouldn’t be any problem with revving high now.

If I’ve forgotten a few things then someone else will probably fill  you  in
on whatever. Happy hooning…!

——— Snail Mail ————– Phone (Aust.) ———– InterNet ——–
Tony Basaranowicz, TA2,         | BH: (03) 660 3204 | t…
Dept. of Comp. Sci.,            |                   | t…
Royal Melbourne Institute       |                   |
   of Technology,               |                   |
124 Latrobe Street, Melbourne,  |                   |
3001, Victoria, Australia.      |                   |

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Re: Exhaust system design literature

gr…@hqda-ai.UUCP (Peter Grant) writes:
> In article <106…@philabs.Philips.Com>, g… (Gert Brunin
> > I am interested in reading a little bit more about exhaust system design
> > theory and practice starting from the exhaust manifold (or header) to the

> Me too!  Please post answer instead of E-mail.  I’ll bet there are at least a
> few other netters also interested in the answer to this query.

> Thanks.

You could try getting ahold of the HP Books, "Performance with Economy"
and "How to Build Horsepower, Vol 1", both by David Vizard.  Excellent
books, both.


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WEBER 40DCOE Series 151 technical spec needed


I am looking for some technical information on the Weber 40DCOE series 151
dual side-draught carbs.  Specifically, I am looking for the technical
specification of the fuel float height, both full open and closed.  I suspect
that the closed position is somewhere around 13 mm and full open is around
25 mm.  The series 151 carb is not listed in the Haynes manual.  Also, the
floats I have are black plastic and have a ’20′ on them (I assume this means
that their weight is 20 grams).  They are NOT the round brass/steel/whatever
floats that the Haynes manual lists (with a ridge around the center that you
are supposed to ignore when setting the float height).  Can anyone help?

Now, to clear up some things about my original 2 posts:

1. The carbs are fitted with K&N air cleaners, which is why (I suspect) that
the Haynes jet settings are too large – they are probably intended to be used
with air horns.  The presence of an air cleaner would create more of a vacuum
inside the carb and thus draw more fuel (in proportions to the amount of air
being taken in).

2. The series 151 carbs have set screws in the side of the bore of each barrel
that hold the choke tube and aux venturi tube in place (each has its own set
screw).  There isn’t any need (or room) to cut off some air horns and place
them in front of the aux venturi to hold it in place.

3. The ‘dripping gas from the progression circuit holes’ has been resolved.
The float levels appear to be too high (thus the reason for this post – I don’t
know what they really should be!).  I discovered also that the center carb
(which was leaking the worst) had a damaged float check valve, causing the
effective float level to be about .065 inches higher than it should be (sorry,
I don’t own a metric caliper gauge).  I set all of the float levels to about
016 inches lower than what they were, and the dripping problem went away.
The float level (fully closed) is now at .516 inches (13.1 mm).  This appears
to be on the hairy edge of having the ‘drips’, but I don’t know how close.

Any help out there from someone with the correct technical reference manual
on the series 151 40DCOE Weber carbs?  Thanks!

 John Gibbons           Allen-Bradley Company         Highland Heights, Ohio

           "Welcome My Son, Welcome To The Machine" – Pink Floyd

  I can be reached at:
       {uunet|pyramid|decvax|cwjcc} !!astro.decnet!gibbonsj
  or some variation of { ? } gibbonsj%astro.dec…
  internet: gibbonsj%iccgcc.dec…
  If all else fails -> voice: (216) 646-3611

           Of all the things I’ve lost, I miss my mind the most…

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'86 CAMRY COLD START problem

I am experiencing a cold start problem with a 1986 CAMRY. This was
discussed about a month ago, but I did not see the final postings due
to news delivery problems. I suspect the cold start injector is
partially clogged due to lower volumes of gas, but I am open to other
suggestions. Any help will be appreciated.

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'86 CAMRY TECHNICS cassette player problem

The cassette player in my 1986 CAMRY has started ‘autoswitching’ from
sided to side and will not stop switching. The cassette is a factory
installed Technics radio/cassette player/equalizer. Has anyone seen
this problem, or know of a shop that could repair the cassette?

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