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?
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 .
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 suppose you might still be able to make it happen but it is probably
tougher on an EFI with all of the emission controls.
On Tue, 17 Mar 2015 10:43:01 -0400, email@example.com wrote:
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 did a google search for
"how to make a tailpipe flamethrower"
Here are several articles which explain how to install a flamethrower on
The first URL is the best of them.
There are many more articles!
Apparently some Hotrod parts stores sell a kit to do this, but they are
On Tue, 17 Mar 2015 21:48:47 -0400, Stormin Mormon
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.
On Tue, 17 Mar 2015 22:53:32 -0400, firstname.lastname@example.org wrote:
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.
On 3/17/2015 10:53 PM, email@example.com wrote:
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
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.
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.
Christopher A. Young
learn more about Jesus
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