Car backfires when turned off

S

Shelbycsx

Senior Member
Was never like this before but every once in a while it will backfire when I shut it off. I noticed that it's really hot by the carb the exhaust manifold looks light in color and maybe too hot. Anyone know what I should check could it be the gaskets for the manifold.
 
The term after fire is a more accurate term for a combustion event through the exhaust but I assume this is what you meant anyway. After the ignition is cut off, the engine continues to draw fuel mixture in a cylinder or two before it it stops turning. Any mixture that is unburned is pushed right back out into the exhaust system where it can somtimes be lit off by a hot spot or a piece of carbon that comes loose in the cylinder during this time. Another possibility is that the ignition switch may have an intermittent internal problem that doesn't completely cut off the circuit when the switch is twisted off or pushed back in if it's an electro-lock. A leaky exhaust valve or valves can also propagate problems like this.

As mentioned by ronn, incorrectly set timing can cause the engine to run hotter than normal which promotes dieseling and possible after fire situations.
 
The motor is running too lean . Before you turn it off open the GAV a few turns that should stop the gas exploding in the muffler .

John in partly cloudy Suffolk County England .
 
Your engine is running too hot which can be caused by a lean mixture or retarded ignition as others have mentioned.

To stop the backfire without changing anything else, turn the fuel off and let the engine idle until it runs out of fuel and dies then turn the ignition off. You can turn the fuel off as you approach your destination. There is enough fuel in the carburetor for a few minutes of running.
 
There is a small window in which the fuel /air ratio is unstable and will more easily ignite . Making the mixture richer takes it out of this window . Engines do run hotter when the mixture is more lean than rich which does not seem logical . This how my engines behave I find if I turn the GAV open for a minute or two before shutting off no muffler explosions .

John in Suffolk County England .
 
Too high of an idle speed can make the problem worse. Easier shifting and other advntages by making sure the idle is slow. If it stalls you have other issues to address.
 
I was preforming a spark plug check, 55mph, turn key off, push the clutch in, backing off the gas………… moment’s later kaboom! the plug’s looked good but my shorts needed changing! Alot of people race there engine’s when shutting off, kaboom! Let idle for a few moments before turning off
 
It’s your timing. To retarded.

Don’t drive the car before you fix the issue. Your head gasket could be the next problem.
 
I'm far from an authority, but I have found that if the GAV is turned almost off the motor will back fire as I get off the gas and make a corner in town. I open the GAV a smidge and the problem disappears.
Good luck.
 
john charlton said:
The motor is running too lean . Before you turn it off open the GAV a few turns that should stop the gas exploding in the muffler .

John in partly cloudy Suffolk County England .
Click to expand...

Or give it more fuel to explode!! :eek: :eek:

john charlton said:
There is a small window in which the fuel /air ratio is unstable and will more easily ignite . Making the mixture richer takes it out of this window .

John in Suffolk County England .
Click to expand...

John, of course you are correct, my lame excuse at a joke...
 
Last edited:
You must log in or register to reply here.
Back
Top