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I have a Hustler Z 52" zero turn mower. about 2 yrs. ago i noticed every now and then a back fire upon shutoff. it wasnt bad then so i just dealt with it. now 2 yrs later it backfires EVERY Time i shut off. I tried all the things i seen on the internet such as cutting off full throttle, half throttle, even choking full and half throttle, tried cooling down engine first that didnt work. let it run idle for 5 min that didnt work. someone said that it is still putting gas into the engine once its off, which when the gas hits the hot engine it causes an explosion and thats the backfire. it litterlaly shoots fire out of the exhaust canister when it blows. sometimes it sounds like a shotgun other times it sounds like a wind of fire, and you can actually see fire coming from exhaust muffler can.

PLEASE I AM DESPREATE FOR HELP AND I HAVE LOOKED EVERYWHERE

You probably need a new fuel shutoff solenoid on the carburetor.

You're probably hearing an 'afterfire' as fuel/air is pumped into the hot exhaust system as the engine is slowing down after turning off the ignition.

That's exactly what the fuel cutoff solenoid is supposed to prevent.

I picked up a Cub Cadet Tank LZ 60 inch used and it does the same thing. I got it cheap and it needed some work. Everything is great now except for this. It starts and runs just fine but boy watch out when you shut it off. BANG!!!

I think they had been running cheap gas with ethanol. My mower guy tells me to run alcohol free premium and that has made so much difference in starting and running, especially if my equipment isn't used for a week or more. I can tell this thing is running a lot better with just the good gas being run through it.

Sometimes it will wait 5-10 seconds before the gas fumes in the muffler cook off and goes BANG and sometimes it does it before the engine has completely stopped turning. Sometimes it is a sharp deafening crack and other times it is a muffled poof. My hunch is that there is something wrong with one of the safety interlocks but I am not sure.

Does this really harm anything or just make a loud bang? I mean flames will shoot out of the exhaust with a bright flash like the muzzle flash from a gun. The mower is now running great besides this issue.

Over time the explosions in the muffler will destroy the muffler.
Mufflers are designed to slow down & cool the exhaust gasses, not to contain an explosion.
The problem stems from the ignorant emission nazis who mandate emission levels for small engines that are way way way too lean.
This means that the exhaust is way , way , way , way too hot so the muffler is red hot internally for quite a long while.
The engine kill stops the sparks so you get a couple of revolutions where there is unburned fuel sent into the muffler.
Air also enters the muffler from the outlet because exhaust is no longer being pushed out.
When the oxygen : fuel ratio gets to between 15:1 and 20:1 you have an explosive mix sitting in the muffler, add a red lot piece of steel & " it goes Bang really loudly daddy" & hurts my ears.
The type &/or quality of the fuel makes no difference.
The only way to stop it happening is to cut the fuel off & let the engine starve off ( Costs $ 5 for a tap ) or replace the very expensive carb solenoid ( costs $50 to $ 100 ) every 10 years or so.

bertsmobile1 said:

Over time the explosions in the muffler will destroy the muffler.
Mufflers are designed to slow down & cool the exhaust gasses, not to contain an explosion.
The problem stems from the ignorant emission nazis who mandate emission levels for small engines that are way way way too lean.
This means that the exhaust is way , way , way , way too hot so the muffler is red hot internally for quite a long while.
The engine kill stops the sparks so you get a couple of revolutions where there is unburned fuel sent into the muffler.
Air also enters the muffler from the outlet because exhaust is no longer being pushed out.
When the oxygen : fuel ratio gets to between 15:1 and 20:1 you have an explosive mix sitting in the muffler, add a red lot piece of steel & " it goes Bang really loudly daddy" & hurts my ears.
The type &/or quality of the fuel makes no difference.
The only way to stop it happening is to cut the fuel off & let the engine starve off ( Costs $ 5 for a tap ) or replace the very expensive carb solenoid ( costs $50 to $ 100 ) every 10 years or so.

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So many things have fixed jets because of the EPA. You can usually buy the special tool for other types off eBay on ones that have the star/spline type adjustment. I have fought with this on other equipment. I bought some consumer grade 2 stroke stuff at Lowes and it was terrible. The jets were set so lean that it was impossible to start. Once started it took like 20 minutes to finally run ok. Once when I was trimming on a hot day, the thing ran away from me. Finally there was a pop and it rattled to a stop. I figured it had thrown a rod but the flywheel key were sheared. This was part of the flywheel which was $75 to replace so I set it out at the curb and was glad to see someone pick it up as a project, for parts, or for scrap metal. I guess it fired out of time when it ran away and tried to run backwards while the thing was just screaming in a runaway mode.

Yes, modern stuff just runs too lean if you ask me. I did try idling it down before turning the mower off today and only got a mild poof out of it. It wasn't like a shotgun. On the other hand, it stalled before it was fully running on the first start and let out a bang like no other. It was started from cold so not related to a hot muffler.