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John Deere Tractors Discussion Forum
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Backfire at half throttle

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37 JD A

05-05-2007 12:03:56




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My 37 unstyled JD A starts and runs good at full throttle. But, when I throttle it down some, it backfires like crazy. Is this a timing issue or is it a carb. issue. I have just overhauled this tractor and the carb has been completely gone over. I am running on gasoline. Any insight to this problem would be appreciated. John




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Lee B

05-06-2007 03:48:43




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 Re: Backfire at half throttle in reply to 37 JD A, 05-05-2007 12:03:56  
That's a mixture problem, you are still a little bit too lean. I find it's almost impossible to get one set where it won't backfire and yet have it not puff a little black smoke at one of the spectrum or the other. Full load or little to no load, idle to full speed. At one place or another in between those extremes, it's awful hard to get one to NOT smoke just a little, just sometimes, just a puff or two.

And then just when you get real close to just right - the next tank of gas requires a whole new set of adjustments... Shutting the gas off and running the tractor until it runs out of gas really saves a lot of this fiddling with the mixture screws due to varnish and gum build up.

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bigblock

05-05-2007 21:57:25




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 Re: Backfire at half throttle in reply to 37 JD A, 05-05-2007 12:03:56  
I adjusted the idle mixture screws on my 730 and stopped the back fireing.



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donwisc

05-05-2007 19:19:39




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 Re: Backfire at half throttle in reply to 37 JD A, 05-05-2007 12:03:56  
Lots of info on this in the archives. One thing you can check without much trouble is disconnect the throttle arm at the carb and operate the carb manually. If it then runs properly it may be in the linkage adjustment. With the butterfly and Accelerator both in the full open position, the linkage rod should come up 1/2 hole short. If not readjust.

I just went thru the same exercise with a AC WD 45 and it cleared up backfiring and surging up and down. This same adjustment is shown in the JD manual if you have one.

Let us know what you find.

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