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Default Can an old timer explain car backfires?

When I was growing up car backfires were common. As a kid I had friends who could make it happen at will.

Now that the carburetor is long gone, most younger folk have never heard one. Fuel injection eliminated this, I think; could be wrong.

I never understood exactly what happens. Usually a car would backfire when under heavy load, and the gas suddenly let up. So my guess is the carburetor had a full charge with nowhere to go. But what ignited it?

Or, possibly the lack of air made an overly rich mixture escape the exhaust valves, and the explosion was in the manifold?
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On Tuesday, March 17, 2015 at 7:11:55 AM UTC-5, TimR wrote:
When I was growing up car backfires were common. As a kid I had friends who could make it happen at will.

Now that the carburetor is long gone, most younger folk have never heard one. Fuel injection eliminated this, I think; could be wrong.

I never understood exactly what happens. Usually a car would backfire when under heavy load, and the gas suddenly let up. So my guess is the carburetor had a full charge with nowhere to go. But what ignited it?

Or, possibly the lack of air made an overly rich mixture escape the exhaust valves, and the explosion was in the manifold?


http://en.wikipedia.org/wiki/Back-fire
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"TimR" wrote in message
...
When I was growing up car backfires were common. As a kid I had friends
who could make it happen at will.

Now that the carburetor is long gone, most younger folk have never heard
one. Fuel injection eliminated this, I think; could be wrong.

I never understood exactly what happens. Usually a car would backfire
when under heavy load, and the gas suddenly let up. So my guess is the
carburetor had a full charge with nowhere to go. But what ignited it?

Or, possibly the lack of air made an overly rich mixture escape the
exhaust valves, and the explosion was in the manifold?




Still happens to me when I eat beans.

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On 3/17/2015 6:20 AM, bob_villa wrote:
On Tuesday, March 17, 2015 at 7:11:55 AM UTC-5, TimR wrote:
When I was growing up car backfires were common. As a kid I had friends who could make it happen at will.

Now that the carburetor is long gone, most younger folk have never heard one. Fuel injection eliminated this, I think; could be wrong.

I never understood exactly what happens. Usually a car would backfire when under heavy load, and the gas suddenly let up. So my guess is the carburetor had a full charge with nowhere to go. But what ignited it?

Or, possibly the lack of air made an overly rich mixture escape the exhaust valves, and the explosion was in the manifold?


http://en.wikipedia.org/wiki/Back-fire


That article was pretty pedantic. What they refer to as backfire is more
popularly called 'carb farts' in the Harley world. Between a primitive
induction system, a wasted spark ignition, and EPA mandated leanness,
pre-FI bikes would tend to blow back through the carburetor. That could
be interesting if you were running without an air filter.

What the OP and most people refer to as a backfire is what the article
calls an afterfire. There were a couple of hills going into town. I'd
cut the ignition on my '51 Chevy and pull the choke as I rolled down in
gear to make sure people knew I was coming.



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On Tue, 17 Mar 2015 05:11:47 -0700 (PDT), TimR
wrote:

When I was growing up car backfires were common. As a kid I had friends who could make it happen at will.

Now that the carburetor is long gone, most younger folk have never heard one. Fuel injection eliminated this, I think; could be wrong.

I never understood exactly what happens. Usually a car would backfire when under heavy load, and the gas suddenly let up. So my guess is the carburetor had a full charge with nowhere to go. But what ignited it?

Or, possibly the lack of air made an overly rich mixture escape the exhaust valves, and the explosion was in the manifold?


Timing caused it. If the distributor was installed off by a tooth or
three. Timing could also slip if the nut loosened a tad.

Carbs caused it. Adjust dual four barrel carbs or three-deuces. Have
to get the cabs in tune. Flooded and it would catch fire so have a
shop rag handy to toss of the carb.

You could push in the clutch in, turn off the ignition, release the
clutch, turn on the ignition and cause a back fire. I was told it
could pop off the top of a piston but I never saw or heard of it
happening


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On Tue, 17 Mar 2015 14:29:38 -0600, wrote:


A fairly common practice among "gear heads" back in the 50's and 60's
was to connect a spark plug right near the tip of the tailpipe.


Horse ****.
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On 03/17/2015 12:41 PM, Oren wrote:
On Tue, 17 Mar 2015 14:29:38 -0600, wrote:


A fairly common practice among "gear heads" back in the 50's and 60's
was to connect a spark plug right near the tip of the tailpipe.


Horse ****.


It usually will if the backfire is loud enough.
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On Tue, 17 Mar 2015 10:43:01 -0400, wrote:


You have 2 kinds of things that might be called backfire. It can pop
back through the carburetor and that might actually indicate a bad
intake valve or you can have a muffler explosion and that is usually a
cessation or failure of ignition (how your buddy made it happen,
flipping the key off and on)
Raw gas builds up in the exhaust and the next time a valve opens on a
burning cylinder, kaboom.
It can split a muffler open.


I did that once when I was young. It just blew the muffler wide open.
Needless to say, that was the LAST time I did it!

A fairly common practice among "gear heads" back in the 50's and 60's
was to connect a spark plug right near the tip of the tailpipe. Somehow
they would use a part often called a "vibrator", which was used in old
vacuum tube car radios to convert DC to AC. That was fed to a capacitor
and a spare ignition coil, which then provided a spark in the spark plug
at the tail pipe outlet. The cars back then, had no catalytic
converters and allowed raw heated gas to exit the exhaust system. That
spark plug ignited those raw gasses and would blow a fairly large flame
out of the tailpipe. It looked "COOL". It was pretty harmless, unless
someone got too close and set their pants or dress on fire!

I suppose you might still be able to make it happen but it is probably
tougher on an EFI with all of the emission controls.


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On Tue, 17 Mar 2015 13:16:21 -0700, Bret Maverick
wrote:

A fairly common practice among "gear heads" back in the 50's and 60's
was to connect a spark plug right near the tip of the tailpipe.


Horse ****.


It usually will if the backfire is loud enough.


Where do you people come from?
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On Tue, 17 Mar 2015 12:41:23 -0700, Oren wrote:

On Tue, 17 Mar 2015 14:29:38 -0600, wrote:


A fairly common practice among "gear heads" back in the 50's and 60's
was to connect a spark plug right near the tip of the tailpipe.


Horse ****.


Hell, they're still doing it. Where you been? In prison?


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On Tue, 17 Mar 2015 15:55:44 -0500, Vic Smith
wrote:

A fairly common practice among "gear heads" back in the 50's and 60's
was to connect a spark plug right near the tip of the tailpipe.


Horse ****.


Hell, they're still doing it. Where you been? In prison?


You two guys sound like hippies.. I did retire as a Penologist though.
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Col. Edmund Burke wrote:
"TimR" wrote in message
...
When I was growing up car backfires were common. As a kid I had
friends who could make it happen at will.

Now that the carburetor is long gone, most younger folk have never
heard one. Fuel injection eliminated this, I think; could be wrong.

I never understood exactly what happens. Usually a car would backfire
when under heavy load, and the gas suddenly let up. So my guess is
the carburetor had a full charge with nowhere to go. But what ignited
it?

Or, possibly the lack of air made an overly rich mixture escape the
exhaust valves, and the explosion was in the manifold?




Still happens to me when I eat beans.


Just hope that doesn't cause a shart...(A combination of a fart and a ****.)

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.
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On Tue, 17 Mar 2015 17:18:40 -0400, Jeff Wisnia
wrote:



Col. Edmund Burke wrote:
"TimR" wrote in message
...
When I was growing up car backfires were common. As a kid I had
friends who could make it happen at will.

Now that the carburetor is long gone, most younger folk have never
heard one. Fuel injection eliminated this, I think; could be wrong.

I never understood exactly what happens. Usually a car would backfire
when under heavy load, and the gas suddenly let up. So my guess is
the carburetor had a full charge with nowhere to go. But what ignited
it?

Or, possibly the lack of air made an overly rich mixture escape the
exhaust valves, and the explosion was in the manifold?




Still happens to me when I eat beans.


Just hope that doesn't cause a shart...(A combination of a fart and a ****.)

Jeff

I thought that was called "having a fit".
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On Tue, 17 Mar 2015 09:39:20 -0700, Oren wrote:

On Tue, 17 Mar 2015 05:11:47 -0700 (PDT), TimR
wrote:

When I was growing up car backfires were common. As a kid I had friends who could make it happen at will.

Now that the carburetor is long gone, most younger folk have never heard one. Fuel injection eliminated this, I think; could be wrong.

I never understood exactly what happens. Usually a car would backfire when under heavy load, and the gas suddenly let up. So my guess is the carburetor had a full charge with nowhere to go. But what ignited it?

Or, possibly the lack of air made an overly rich mixture escape the exhaust valves, and the explosion was in the manifold?


Timing caused it. If the distributor was installed off by a tooth or
three. Timing could also slip if the nut loosened a tad.

Carbs caused it. Adjust dual four barrel carbs or three-deuces. Have
to get the cabs in tune. Flooded and it would catch fire so have a
shop rag handy to toss of the carb.

You could push in the clutch in, turn off the ignition, release the
clutch, turn on the ignition and cause a back fire. I was told it
could pop off the top of a piston but I never saw or heard of it
happening

Well, as a mechanic I can say definitely it could NOT damage a piston
- as the "explosion" was not in the engine.
Bad ignition was responsible for more exhaust bachfires than bad
carburetion. My Dad's '69 GMC pickup had a bad habit of slitting the
muffler every 6-8000 miles unless you changed the points first. Ends
up the factory had not installed the ground wire between the points
plate and the distributor housing, so the points burned badly - and
intermittent spark would allow the muffler to load up with gas when
the spark was off, and then light when it came back on.

An exhaust leak could also cause exhaustr backfire on decel or
over-run as the exhaust was rich with gas from the high vacuum, and
added air into a hot pipe would light it off, giving
bang-bang-bang-BANG!!! coming down a hill.

One day with 22 tons of farm equipment on the float behind the 292
GMC, I came down a long gentle hill to a narrow bridge across a creek
where guys were working on the road.. They were in no hurry to get out
of the way as I came towards them, so I shut off the ignition for a
second or two, then turned it back on. They jumped out of the way
real quick!!!. (had a drawn steel "cherry bomb" muffler on it that
withstood backfires quite well - after blowing a few Thrush cans off
of it.
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rbowman wrote:
On 3/17/2015 6:20 AM, bob_villa wrote:
On Tuesday, March 17, 2015 at 7:11:55 AM UTC-5, TimR wrote:
When I was growing up car backfires were common. As a kid I had
friends who could make it happen at will. Now that the carburetor is
long gone, most younger folk have never
heard one. Fuel injection eliminated this, I think; could be
wrong. I never understood exactly what happens. Usually a car would
backfire when under heavy load, and the gas suddenly let up. So my
guess is the carburetor had a full charge with nowhere to go. But
what ignited it? Or, possibly the lack of air made an overly rich
mixture escape the
exhaust valves, and the explosion was in the manifold?


http://en.wikipedia.org/wiki/Back-fire


That article was pretty pedantic. What they refer to as backfire is
more popularly called 'carb farts' in the Harley world. Between a
primitive induction system, a wasted spark ignition, and EPA mandated
leanness, pre-FI bikes would tend to blow back through the
carburetor. That could be interesting if you were running without an
air filter.
What the OP and most people refer to as a backfire is what the article
calls an afterfire. There were a couple of hills going into town. I'd
cut the ignition on my '51 Chevy and pull the choke as I rolled down
in gear to make sure people knew I was coming.


We had a Mazda RX3 , if you let off the throttle coming down a hill , it
would come out with a VERY loud backfire . Something to do with one of the
two sets of points being off just a hair IIRC .
Anyway , we were coming down a not-too-steep hill into Brigham City Utah ,
and the traffic light at the bottom of the hill was out ... and there was a
Highway Patrol trooper directing traffic ... and I let off on the throttle
just right ... and that damn car blew just as we passed the trooper . When I
looked in my mirror , he was on the ground with his gun drawn and looking
for who shot at him . I still chuckle when I think about that . That
particular trooper was a real asshole or I wouldn't have done it .

--
Snag




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Oren wrote:
On Tue, 17 Mar 2015 15:55:44 -0500, Vic Smith
wrote:

A fairly common practice among "gear heads" back in the 50's and
60's was to connect a spark plug right near the tip of the
tailpipe.

Horse ****.


Hell, they're still doing it. Where you been? In prison?


You two guys sound like hippies.. I did retire as a Penologist though.


We're sorry .

What wasn't said was that there was also a way to deliver a mist of fuel
just ahead of that spark plug . Made a most awesome flamethrower . Didn't do
it , but I did see it .

--
Snag


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TimR wrote:
When I was growing up car backfires were common. As a kid I had
friends who could make it happen at will.

Now that the carburetor is long gone, most younger folk have never
heard one. Fuel injection eliminated this, I think; could be wrong.

I never understood exactly what happens. Usually a car would
backfire when under heavy load, and the gas suddenly let up. So my
guess is the carburetor had a full charge with nowhere to go. But
what ignited it?

Or, possibly the lack of air made an overly rich mixture escape the
exhaust valves, and the explosion was in the manifold?


My '94 caravan started backfiring several months ago. Replacing the ignition
wires solved the problem.


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TimR wrote:
When I was growing up car backfires were common. As a kid I had friends
who could make it happen at will.

Now that the carburetor is long gone, most younger folk have never heard
one. Fuel injection eliminated this, I think; could be wrong.

I never understood exactly what happens. Usually a car would backfire
when under heavy load, and the gas suddenly let up. So my guess is the
carburetor had a full charge with nowhere to go. But what ignited it?

Or, possibly the lack of air made an overly rich mixture escape the
exhaust valves, and the explosion was in the manifold?


I think muffler backfire can be from too rich. Carb or intake backfire, too
lean. I had backfire in a datsun. I had to readjust airflow meter.

Greg


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On Tue, 17 Mar 2015 22:53:32 -0400, wrote:

Well, whether it was technically pulsed DC or AC coming out of the
vibrator, what came out of the transformer was AC, as it required
rectification to turn it back to DC. AC or pulsed DC from the vibrator
is just semantics.


An automotive coil is just a transformer that raises 12v to a very high
voltage. But all transformers require AC to make them work. But you
are correct, it's pulsed DC, but to the transformer, it's the same as
AC. The points in older engines simply pulsed the DC. The newer
electronic ignitions do a similar thing, but they may be more like
actual AC (I'm not sure).

Now a days, one could use an electronic ignition module, like one from a
small mower engine, or one made for cars (which would be overkill). For
this use, it really dont much matter what makes the pulse as long as
there *IS* a pulse to trigger the coil. A set of points could be used
to, but there would need to be soem sort of cam external to the engine.
So, an electronic module or a one of those old radio vibrators is/was a
much easier method to excite the coil.

Someone mentioned in this thread about injecting a spray of gas into the
pipe to make a bigger flame. Yes, I heard of that too, but I did not
mention it because I have no clue how that was accomplished. In fact
I'd like to find out how. Not that I want to do it, but I like to know
stuff like that. However, to take a wild guess, I'm thinking in terms
of the nozzle inside an oil furnace. Something like that welded into
the tailpipe, would send a spray of fuel, bu there would need to be a
pump of some sort. But attaching a pump of some sort, to the engine's
fan belt, or a pump running off a 12V motor (such as a heater blower
motor), would probably work fine. (Just a guess).

To make a "flamethrower" from the exhaust pipe, would probably require
injecting fuel into the pipe now-a-days, because newer car engines with
catalytic converters are intended to NOT release any raw fuel. But I
bet my old late 1940's Farmall tractor would work just fine. I can
smell the unburned gas when it's running. But I recall smelling that
same odor from the tailpipe on the old cars that I drove in the late
60's and early 70's. (which were 50's and 60's cars with carburetors and
no air pollution devices).

Now-a-days, a person would probably be arrested and ticketed for doing
something like that on a vehicle driven on public roads, but I could see
doing it at a truck or tractor pull, or just doing it for fun on an old
farm vehicle or anything that is not used on public roads.



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On 3/17/2015 6:42 PM, Terry Coombs wrote:
We had a Mazda RX3 , if you let off the throttle coming down a hill , it
would come out with a VERY loud backfire . Something to do with one of the
two sets of points being off just a hair IIRC .
Anyway , we were coming down a not-too-steep hill into Brigham City Utah ,
and the traffic light at the bottom of the hill was out ... and there was a
Highway Patrol trooper directing traffic ... and I let off on the throttle
just right ... and that damn car blew just as we passed the trooper . When I
looked in my mirror , he was on the ground with his gun drawn and looking
for who shot at him . I still chuckle when I think about that . That
particular trooper was a real asshole or I wouldn't have done it .


While I can't totally approve of treating LEO like
this, I will admit to smiling as I was reading.

-
..
Christopher A. Young
learn more about Jesus
.. www.lds.org
..
..
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On 3/17/2015 10:53 PM, wrote:
On Tue, 17 Mar 2015 21:48:47 -0400, Stormin Mormon

It's been a lot of years, but I recall a vibrator
created pulsating DC, which could be put through a
transformer. Not AC.

-
.
Christopher A. Young
learn more about Jesus
.
www.lds.org
.
.

Well, whether it was technically pulsed DC or AC coming out of the
vibrator, what came out of the transformer was AC, as it required
rectification to turn it back to DC. AC or pulsed DC from the vibrator
is just semantics.

But then Stormy knows that.


I could not find a web page that described the old
type vibrators (not the kind that give women momentary
high blood pressure and screaming and moaning). But
what I remember is they caused a rapid interruption in
the DC, by open and close a switch / contacts. As such
they put out pulasting DC, which ended up being
pulsating DC on the other side of the transformer.

OTOH, this was a couple decades ago I learned of these.

AC goes through the transformer just fine, but DC does
not. Which is why the vibrator is needed. But, then,
Clare knows that.

-
..
Christopher A. Young
learn more about Jesus
.. www.lds.org
..
..
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http://i1181.photobucket.com/albums/...psd6634c71.gif

also, a new opportunity for Stormy: http://i1181.photobucket.com/albums/...00babfbd.jp g
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On Tue, 17 Mar 2015 15:55:44 -0500, Vic Smith
wrote:

On Tue, 17 Mar 2015 12:41:23 -0700, Oren wrote:

On Tue, 17 Mar 2015 14:29:38 -0600, wrote:


A fairly common practice among "gear heads" back in the 50's and 60's
was to connect a spark plug right near the tip of the tailpipe.


Horse ****.


Hell, they're still doing it. Where you been? In prison?



I did a google search for
"how to make a tailpipe flamethrower"

Here are several articles which explain how to install a flamethrower on
your tailpipe.
The first URL is the best of them.

http://www.astrosafarivans.com/bb2/v...&t=497&start=0

http://www.jalopyjournal.com/forum/t...hrower.728822/

http://www.instructables.com/answers...ust-flame-kit/

VIDEO
https://www.youtube.com/watch?v=ExgtYK5rpi0


There are many more articles!

Apparently some Hotrod parts stores sell a kit to do this, but they are
costly.



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"Jeff Wisnia" wrote in message
...


Col. Edmund Burke wrote:
"TimR" wrote in message
...
When I was growing up car backfires were common. As a kid I had
friends who could make it happen at will.

Now that the carburetor is long gone, most younger folk have never
heard one. Fuel injection eliminated this, I think; could be wrong.

I never understood exactly what happens. Usually a car would backfire
when under heavy load, and the gas suddenly let up. So my guess is
the carburetor had a full charge with nowhere to go. But what ignited
it?

Or, possibly the lack of air made an overly rich mixture escape the
exhaust valves, and the explosion was in the manifold?




Still happens to me when I eat beans.


Just hope that doesn't cause a shart...(A combination of a fart and a
****.)

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.



LOL

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"Stormin Mormon" wrote in message
news

I could not find a web page that described the old
type vibrators (not the kind that give women momentary
high blood pressure and screaming and moaning). But
what I remember is they caused a rapid interruption in
the DC, by open and close a switch / contacts. As such
they put out pulasting DC, which ended up being
pulsating DC on the other side of the transformer.


On the output side of the transformere it was AC. That is why a rectifier
tube or diode was used. The 0Z4 was a common tube used in the old car
radios. There were some syncronous vibrators that had a set of points on
the secondary and another on the primary. This eliminated the need for the
rectifier and only the capacitors were needed to smooth out the pulsing DC.


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On 3/18/2015 10:05 AM, Ralph Mowery wrote:
"Stormin Mormon" wrote in message
news

I could not find a web page that described the old
type vibrators (not the kind that give women momentary
high blood pressure and screaming and moaning). But
what I remember is they caused a rapid interruption in
the DC, by open and close a switch / contacts. As such
they put out pulasting DC, which ended up being
pulsating DC on the other side of the transformer.


On the output side of the transformere it was AC. That is why a rectifier
tube or diode was used. The 0Z4 was a common tube used in the old car
radios. There were some syncronous vibrators that had a set of points on
the secondary and another on the primary. This eliminated the need for the
rectifier and only the capacitors were needed to smooth out the pulsing DC.


(reply from a friend of mine)
it's the same as the spark plug circuit on the ignition.

It's not AC, it's pulsed DC.

http://hyperphysics.phy-astr.gsu.edu.../ignition.html


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"Stormin Mormon" wrote in message
...
On 3/18/2015 10:05 AM, Ralph Mowery wrote:
(reply from a friend of mine)
it's the same as the spark plug circuit on the ignition.

It's not AC, it's pulsed DC.

http://hyperphysics.phy-astr.gsu.edu.../ignition.html



Using a viberator is differant than the opening and closing of the points of
an engine. By the way that diagram is not correct. "The condenser goes
across the points. It is there to prevent arcing. It does this by slowing
down the colapsing of the magnetic field which produces the other half of
the AC waveform.


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Default Can an old timer explain car backfires?

On 3/18/2015 12:16 PM, Stormin Mormon wrote:

It's not AC, it's pulsed DC.

http://hyperphysics.phy-astr.gsu.edu.../ignition.html


(from another friend)


The original purpose of the Vibrator was in the power supply of early
car radios. The Vibrator would make pulsed DC to drive the transformer
to make the B+ (Typically 300 Volts) and C voltage (Typically around 45
Volts) to run the old High Voltage tubes.

When I was Young and Dumb, I had a 1972 Impala 454 SS with dual exhaust.
I made me a Vibrator powering a pair of Ignition Coils driving a pair of
Spark Plugs I mounted in the exhaust tips. When I flipped the switch, it
would throw flames about 3 or 4 Feet long out of the back.

This trick works best on Pre-1974 EPA cars then the newer ones.


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On 3/18/2015 12:32 PM, Ralph Mowery wrote:

http://hyperphysics.phy-astr.gsu.edu.../ignition.html



Using a viberator is differant than the opening and closing of the points of
an engine. By the way that diagram is not correct. "The condenser goes
across the points. It is there to prevent arcing. It does this by slowing
down the colapsing of the magnetic field which produces the other half of
the AC waveform.


Just had a more serious look at that diagram. The points
ign I've worked on, B+ goes to ballast resistor, to coil.
Points switch the - side of the coil, with condensor going
from points to ground. So, I also question the accuracy
of that diagram.

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Default Can an old timer explain car backfires?

On Tue, 17 Mar 2015 17:56:47 -0400, wrote:

On Tue, 17 Mar 2015 09:39:20 -0700, Oren wrote:

On Tue, 17 Mar 2015 05:11:47 -0700 (PDT), TimR
wrote:

When I was growing up car backfires were common. As a kid I had friends who could make it happen at will.

Now that the carburetor is long gone, most younger folk have never heard one. Fuel injection eliminated this, I think; could be wrong.

I never understood exactly what happens. Usually a car would backfire when under heavy load, and the gas suddenly let up. So my guess is the carburetor had a full charge with nowhere to go. But what ignited it?

Or, possibly the lack of air made an overly rich mixture escape the exhaust valves, and the explosion was in the manifold?


Timing caused it. If the distributor was installed off by a tooth or
three. Timing could also slip if the nut loosened a tad.

Carbs caused it. Adjust dual four barrel carbs or three-deuces. Have
to get the cabs in tune. Flooded and it would catch fire so have a
shop rag handy to toss of the carb.

You could push in the clutch in, turn off the ignition, release the
clutch, turn on the ignition and cause a back fire. I was told it
could pop off the top of a piston but I never saw or heard of it
happening

Well, as a mechanic I can say definitely it could NOT damage a piston
- as the "explosion" was not in the engine.
Bad ignition was responsible for more exhaust bachfires than bad
carburetion. My Dad's '69 GMC pickup had a bad habit of slitting the
muffler every 6-8000 miles unless you changed the points first. Ends
up the factory had not installed the ground wire between the points
plate and the distributor housing, so the points burned badly - and
intermittent spark would allow the muffler to load up with gas when
the spark was off, and then light when it came back on.

An exhaust leak could also cause exhaustr backfire on decel or
over-run as the exhaust was rich with gas from the high vacuum, and
added air into a hot pipe would light it off, giving
bang-bang-bang-BANG!!! coming down a hill.

One day with 22 tons of farm equipment on the float behind the 292
GMC, I came down a long gentle hill to a narrow bridge across a creek
where guys were working on the road.. They were in no hurry to get out
of the way as I came towards them, so I shut off the ignition for a
second or two, then turned it back on. They jumped out of the way
real quick!!!. (had a drawn steel "cherry bomb" muffler on it that
withstood backfires quite well - after blowing a few Thrush cans off
of it.


It was easy to make a Model A Ford backfire. Soak a little gas on a
rag, slip muffler back a tad, backfire and light the rag. Fire up your
cigarette

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On Tue, 17 Mar 2015 17:45:39 -0500, "Terry Coombs"
wrote:

What wasn't said was that there was also a way to deliver a mist of fuel
just ahead of that spark plug . Made a most awesome flamethrower . Didn't do
it , but I did see it .


Ah. I see what you mean.

Pilots mist something on an engine exhaust to make smoke in the sky.

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On Tue, 17 Mar 2015 18:11:20 -0700, "Bob F"
wrote:

My '94 caravan started backfiring several months ago. Replacing the ignition
wires solved the problem.


Had an old Chevy with bad plug wires - cracked and brittle. During a
heavy rain, wet wire - that Chevy made a racket misfiring. Under the
hood was a light show.

Yeah. New wires help.
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