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Tractor Talk Discussion Forum

Tractor backfires after turned off

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al bane

08-02-2005 06:37:04




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I have a Farmall 300 tractor that runs with a slight miss and after you use it for a while and turn it off , in about 5-10 seconds, it backfires and sounds about like a 410 shotgun. what could be the cause--al bane




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Pa. Don

08-12-2005 03:28:38




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 Re: Tractor backfires after turned off in reply to al bane, 08-02-2005 06:37:04  
I had the same problem with my 300. One day I decided to change it to a mag ignition. Set the timing by the book and when I started it up, that was the first time since I bought it that it sounded like a farmall. It always had sort of a blatting sound to it.(Sorry but that's the best way I know to describe the sound) The backfiring stopped to. I was always 'ready' to send it down the road, but since I put a mag on it you'd have a hard time getting me to part with it.

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Bret4207

08-02-2005 15:57:14




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 Re: Tractor backfires after turned off in reply to al bane, 08-02-2005 06:37:04  
We call that an "Uncle Buck". See the movie and you'll know why. Jeeze I miss John Candy.



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Joe (Wa)

08-02-2005 14:44:21




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 Re: Tractor backfires after turned off in reply to al bane, 08-02-2005 06:37:04  
The term is afterfire. The problem is generally fuel/air mixture either too lean or too rich. Either condition causes a slow burn rate. Combustion is still in progress when the exhaust valve opens. The burning fuel/air mixture is dumped into the exhaust manifold and is immediately snuffed out for lack of oxygen to support combustion. As the engine is running, most of the unburned mixture continues up the stack and vaporizes off.

When you shutdown the engine, some of the unburned mixture remains in the manifold and is well above ignition temperature but lacks sufficient oxygen. The exhaust gas is displaced by cooler, heavier, oxygen rich air. When enough incoming fresh air is present to support combustion it pops off.

Joe

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Don L C

08-02-2005 12:47:51




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 Re: Tractor backfires after turned off in reply to al bane, 08-02-2005 06:37:04  
Mostlikley an edge of carbon was glowing red hot and ignated the fuel mixture in that cylinder after shut down....the exhaust valve just happen to be open.....my 2cents Don S.W.ohio



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al bane

08-02-2005 11:57:39




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 Re: Tractor backfires after turned off in reply to al bane, 08-02-2005 06:37:04  
I do let the engine idle for a while before I turn the switch off and it still does that--al bane



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hay

08-02-2005 09:37:15




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 Re: Tractor backfires after turned off in reply to al bane, 08-02-2005 06:37:04  
check the engine timing. if it is off even a slight bit in some older engines, that can cause missing and backfiring. also pull the spark plugs and check for heavy carbon buildup and or a carbon chip on the plug electrode.



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RustyFarmall

08-02-2005 09:32:26




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 Re: Tractor backfires after turned off in reply to al bane, 08-02-2005 06:37:04  
The easiest way to cure that problem is to let the tractor sit and idle for a couple of minutes and allow the engine to cool down before you shut it off. I really don"t think you have a carburetor problem, even if the carb was set too rich you would have other, more noticeable problems. Allowing the engine to cool down before you shut it off is a good idea on any tractor, I have witnessed engines that backfired after shut down, and actually ruptured the muffler.

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RustyFarmall

08-02-2005 09:56:59




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 Re: Tractor backfires after turned off in reply to RustyFarmall, 08-02-2005 09:32:26  
Also, that slight miss could be caused by a bad engine valve, possibly an intake valve, which would also contribute to the backfiring. The valve lash may just need adjusting.



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al bane

08-02-2005 08:51:19




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 Re: Tractor backfires after turned off in reply to al bane, 08-02-2005 06:37:04  
does thos mean that the float should be higher or lower in the carb-



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old

08-02-2005 09:27:18




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 Re: Tractor backfires after turned off in reply to al bane, 08-02-2005 08:51:19  
Its not a float problem but a setting problem. You need to turn the main jet in a 1/2 to 1 turn. Start it up and adjust the main jet till you here the engine slow down and then go back out til it smooths out again and give that a try. You may have to play with it some to get it just right.



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old

08-02-2005 08:20:05




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 Re: Tractor backfires after turned off in reply to al bane, 08-02-2005 06:37:04  
sounds like you may have the carb set a little to rich which would cause it to back fire when you shut it off. Being set to rich would also cause it to miss a little also



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Mark - IN.

08-02-2005 16:12:16




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 Re: Tractor backfires after turned off in reply to old, 08-02-2005 08:20:05  
Mmm Hmm. With no further info, sounds like the best guess of "been there, done that" experience. Pull and check them plugs, am guessing are black with soot. Just a first guess.

Mark



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dhermesc

08-02-2005 08:53:00




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 Re: Tractor backfires after turned off in reply to old, 08-02-2005 08:20:05  
Agreed. My 350 was doing the same thing after the carb was rebuilt. Once in the while when it gets worked HARD it will still backfire at shut don - lot of carbon in that old engine.



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Illinois Boy

08-02-2005 11:18:41




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 Re: Tractor backfires after turned off in reply to dhermesc, 08-02-2005 08:53:00  
If it wasn't for the carbon, my engine probably wouldn't have any cylinder walls...



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