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Boom

massey kohler

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#1 noclue OFFLINE  

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Posted March 03, 2012 - 02:30 PM

i have a massey 14 with a rebuilt kohler k321 and when i shut it off it backfires! not when i turn the key off, but when the motor stops turning boom! any thoughts on why it does this let me know because i'm stumped.

#2 JDBrian OFFLINE  

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Posted March 03, 2012 - 02:47 PM

That sounds familiar. The 321 on my JD314 did that as well when I first got it. The timing was off due to the points being worn and out of adjustment. Once that was sorted out the backfiring and running on stopped. It would make you jump when you turned off the key and the engine would stop then Bang! Loud enough to scare you! The other problem that my engine had was that the head gasket was blown. I'd check the timing/points first. The points pushrod can be the source of problems as well. Some of them are plastic and can wear and stick. Good luck with it.
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#3 Amigatec OFFLINE  

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Posted March 03, 2012 - 02:56 PM

My Cub 129 has done this from day one. I rebuilt the motor and bought a new Carb and points and it still does it.

#4 HDWildBill ONLINE  

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Posted March 03, 2012 - 03:00 PM

I agree with Brian, check your timing/ points. Make sure everything looks good and has the proper settings. Next I would check for air leaks in the intake and exhaust.
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#5 DH1 ONLINE  

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Posted March 03, 2012 - 03:04 PM

Sometimes if you have a small hole in the muffler near the exhaust port it causes a boom when you turn the engine off.
I think ??? exhaust gasses leak out the hole then air is drawn in, pulses if you will, as the engine runs pulses flow through the muffler.
When you shut it off the exhaust has unburned fuel in it plus the air that's drawn in, acting with the heat of the muffler, when it's just right, BOOM.
I have no way to prove this.
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#6 HDWildBill ONLINE  

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Posted March 03, 2012 - 03:19 PM

Doug you are correct. I see this on motorcycles quite often. Someone will change out there stock muffler with an open or free flow one and then the bike will start popping on decel. What is happening is cool air is now allowed to be drawn in to the muffler and mixed with the hot gasses which not bumps up the AFR and then it pops.

#7 MH81 ONLINE  

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Posted March 03, 2012 - 03:21 PM

I agree with the points / timing / muffler, it sure would be worth it to check.

My GT5000 manual with the Kohler Command specifies running at idle for at least a minute before shutdown. If I don't, it makes one heck of a backfire.

Does yours do it if it's been idling for a little bit?
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#8 Gary400 OFFLINE  

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Posted March 03, 2012 - 04:22 PM

the JD L130 i use to have done it also and it had a kohler command . if i didnt let it idle for a few minutes it would sound like it was blowing the muffler off . some times i would be off the mower than it would do it .

#9 caseguy OFFLINE  

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Posted March 03, 2012 - 04:41 PM

My Kohler Magnum 14 has done it since I've owned it as well. It is less pronounced when I let it idle down first before turning it off. The 23 HP Briggs and Stratton on my zero turn does it also, also from the time it was new. It was explained to me that it is caused by the continued rotation of the engine after the ignition is shut off drawing air/fuel mixture into the cylinder and exiting through a hot exhaust valve and igniting either there or in the muffler. On some of the newer carbs, there is an "anti-afterfire solenoid" that shuts the fuel off the second that the ignition is cut thereby preventing this from happening. I recently worked on a friend's 2006 Kohler Command with the AAS installed and it does not backfire on shutdown.

#10 broken2 OFFLINE  

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Posted March 03, 2012 - 09:33 PM

Without knowing the particulars about you tractor or situation I can only mention a few things. It's always best to shut the tractor off at an idle so the engine dosen't continue to turnover as long and draw fuel/air into the cylinder. I always let it idle for a while to cool down before I shut it off, especialy if it is hot outside or if the engine has been working hard. I would also make sure that the cooling fins and engine shields are clear so it is cooling properly. A hot engine is more likley to deisel or backfire at shut down. Once the ignition is shut off there is no spark for the engine to fire, only stored heat and compression. A lean running engine will also run hot and can cause backfiring. If you go to a less restrictive exhaust, it will lean out your air/fuel mixture.

Edited by broken2, March 03, 2012 - 09:34 PM.


#11 IamSherwood OFFLINE  

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Posted March 04, 2012 - 01:26 AM

I have the same issue on one of my K341s. It's so loud, the dogs run away. They hate gun shots.
If I let it idle for 45 seconds or so, no backfire after shutdown. But, sometimes I forget, and I worry
about what damage might get done.

#12 JDBrian OFFLINE  

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Posted March 05, 2012 - 11:04 AM

The lean running thing is something I had as well now that I think of it. The head gasket was shot and leaking badly so I had lots of problems. The behavior was the same as described. Could be a combination of things. It's not helped on the JD's by the recommended idle speed which is 2200rpms.

#13 ducky OFFLINE  

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Posted March 05, 2012 - 11:43 AM

I am with Will. Leave it idle for a minute or two before turning the key off.

#14 mjodrey OFFLINE  

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Posted March 05, 2012 - 11:46 AM

I am with Will. Leave it idle for a minute or two before turning the key off.



Ditto! I also agree with this.

#15 TUDOR OFFLINE  

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Posted March 05, 2012 - 01:35 PM

I've always idled my engines to shut them off, but when I got my Husqvarna with a Briggs, the manual states:

"STOPPING

- Move throttle control (D) between half and full speed (fast) position.

NOTE: Failure to move throttle control between half and full speed (fast) position, before stopping, may cause engine to "backfire"."

They weren't kidding! Big boom at idle.

Lord, it's hard to change a 55 year old habit!!

Edited by TUDOR, March 05, 2012 - 01:44 PM.

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