backfire

[3mzcubbie]

happy fathers day to everyone,
my question is what causes a backfire and is this a serious problem ? after i cut for an hour or so and turn the engine off, after about 10 or15 seconds it will let out a single backfire. is this fixable or do i have to live with it?
matt

 

[Fordlords]

This is common and not harmful, just annoying. One way that is said to stop it is to shut the engine off while it's throttled up instead of idling down.

What happens is after you turn the key off, the engine still spins a few revolutions allowing gas to purge through the engine in to the muffler, where the heat is enough to ignite it causing the backfire. At throttle the mixture is leaner and won't tend to ignite in the muffler.

-Fordlords-

 

[TractorLarry]

Hehe. Welcome to the BCOM (Backfire Club Of America)

We all get this. It's one of those obnormal things that's normal.

I believe it's caused by raw fuel igniting in the exhaust when you shut the engine off. Since the spark is killed, and cannot burn the fuel normally, the fuel hits the hot exhaust instead, where it ignites.

There are several ways to improve this (there is no fix). Some work better than others for certain folks.

1. Allow the engine to idle for at least 3 minute prior to shut-down to allow the exhaust to cool.

2. Just before you shut the engine off, run the throttle up to 2/3, then kill the ignition.

I've done both and they both work.

-Larry

happy fathers day to everyone,
my question is what causes a backfire and is this a serious problem ? after i cut for an hour or so and turn the engine off, after about 10 or15 seconds it will let out a single backfire. is this fixable or do i have to live with it?
matt

 

[OhioGuy]

This also appears to be model specific, my 5252 doesn't backfire if I turn it off at or above half throttle.

The 1872 needs to be throttled all the way down.

Whatever you're currently doing, try the opposite approach

Good Luck!
Curt

 

[mrutkaus]

Wouldn't say not harmful, blew out side of muffler on 782 last week!!

If carb adjusted right, usually does NOT happen, IMHO in two cadets over 30 yrs.

Mike

 

[Fordlords]

Yowzers- I guess integrity of the muffler could make a difference if it's harmful or not. My 682 never did the backfire thing with the Kohler, nor does it do it with the Honda, I figured the only ones that did that were engines with their mufflers facing downwards.

-Fordlords-

 

[OhioGuy]

Just about every Cub I ever owned had two anomolies.
They all backfire now and then, some more than others and they almost all would be difficult to start if they were warmed up real well and then shut off for say, a beer break.

They would usually starte just fine after a three beer break and I never felt any strong desire to investigate further.

Curt

 

[JTKub]

For what ever reason, the 'after-fire' seems to be a feature on some of the larger Briggs Inteks and Kohler Commands. My Cheapy Walmart Yard Machines 17hp Briggs single did it if you s/d at idle, and my CC Kohler Command 20 will do it almost every time if s/d at idle once she's hot. I dunno if it's an exhaust system issue or an "EPA" carburetor issue. Both of my *bangers* had the fuel cutoff solenoid on the carb bowl. OTOH, our JD with the Kawasaki 17hp single never banged. Dunno what is up with that.

Joel

 

[Northstar]

Here is what Kohler has to say :
"Why does my engine backfire when I shut it off?

Your owners manual has proper shutdown procedures to avoid this occurrence. If your engine is equipped with a fuel shut-off solenoid, be certain to set the throttle between half and full throttle before turning the key switch "off."

They also recommend an octane rating of 87 or higher. I have found they don't backfire if you use a higher octane, if you want to spend the extra money.

 

[3mzcubbie]

thanks for all the input guys, my online manual said shut the engine down at half throttle. i ll try a few of your tips to see what works for me.
thanks,3mz.