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JD620 FOUL

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lurch

08-03-2000 17:41:16




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Have 620 that fouls spark plugs "BLACK". Have 90 over pistons, new rings, valves, seats, cam, intake, rebuilt carb. Runs GREAT for approx. 3-4 hours under load and then fouls out # 1 first. I can pull plug wire 1/4 inch off plug and run 3 more hours until plug dies.




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buckeye al

08-09-2000 15:48:14




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 Re: JD620 FOUL in reply to lurch, 08-03-2000 17:41:16  
I agree with JDGnut, G taylor & Old John T. For some reason you're running too rich. Lean it down & don't use Champion D16's unless it's a hard work tractor. Champion only recommends D16's for heavy service. For normal service they recommend D21's. I use the D23's for light service & parades. They last for years unless run too rich. Then they'll foul & they become driveway gravel.



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Mike Aylward

08-04-2000 05:57:41




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 Re: JD620 FOUL in reply to lurch, 08-03-2000 17:41:16  
Lurch, you have described the classic symptom of a Champion spark plug in a two-cylinder John Deere. If they will fire at all this is usually what they will end up doing. As JDGNut says, put in a pair of Autolites. You will be much happier, and so will your tractor. A 388 plug is two or three heat ranges hotter than a 386. The 386 is the plug I use all the time and a match for your D16, and either should work fine. If you are going to put your tractor to work anytime the cooler plug will be more satisfactory. If it will only see light work, the 388 will be your best choice. Hope this helps. Mike

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Mike Aylward

08-04-2000 05:57:23




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 Re: JD620 FOUL in reply to lurch, 08-03-2000 17:41:16  
Lurch, you have described the classic symptom of a Champion spark plug in a two-cylinder John Deere. If they will fire at all this is usually what they will end up doing. As JDGNut says, put in a pair of Autolites. You will be much happier, and so will your tractor. A 388 plug is two or three heat ranges hotter than a 386. The 386 is the plug I use all the time and a match for your D16, and either should work fine. If you are going to put your tractor to work anytime the cooler plug will be more satisfactory. If it will only see light work, the 388 will be your best choice. Hope this helps. Mike

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Paul from Michigan

08-03-2000 19:03:00




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 Re: JD620 FOUL in reply to lurch, 08-03-2000 17:41:16  
Sounds like you have met up with the unleaded gas plug fouling GOD. I have trouble with all of my two cylinders unless they are really working hard. This wasn't a problem until we had to use the unleaded gas. Maybe an electronic ignition like new cars would help. Meanwhile I clean a lot more plugs than I should. Good luck, Paul



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John T

08-03-2000 18:48:37




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 Re: JD620 FOUL in reply to lurch, 08-03-2000 17:41:16  
Assuming your new rings are properly seated it sounds from your description like your fouling from excess gas (black) instead of oil. That can be caused by over rich carb settings (or even an intake air restriction) or a plug running at too low a heat range. Try adjusting the carb a bit leaner or a plug with one or two hotter ranges. I can explain the extra plug gap trick if you need, but for now try leaner carb settings or hotter plugs and be sure the air cleaner is free. Ol John T in Indiana

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JDGnut

08-03-2000 19:38:17




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 Re: Re: JD620 FOUL in reply to John T, 08-03-2000 18:48:37  
Ol John T said try a hotter plug.. try a Autolite 388... most of the JD dealer have the Autolite plugs.. but most only have the 386.. the 388 is a hotter plug... they will be in a John Deere box..
JDGnut



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G Taylor lean is clean, we usualy run Champions just fine

08-04-2000 07:39:38




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 Re: Re: Re: JD620 FOUL in reply to JDGnut, 08-03-2000 19:38:17  
My 620 runs just fine with the main jet turned all the way in and idle screws open only 3/4 turn. Coolant temp is 180 F. Most people get into trouble with a parade tractor running without a thermostat or with the shutters wide open with OLD fuel and the carb set ultra rich for smooth running and easy starting without the choke. In fact they usualy brag they rairly need to use the choke. The combustion chamber can be so cold the gasoline vapour condenses on the metal like your breath on a cold window pane. One of the reasons why rings fail to seat or wear quickly and the oil is thinned with raw gasoline. Gasoline has the same shelf life at 70F as milk does at 35F. No wonder so many collector's tractors with a portion of the fuel several years old have trouble. Most guys set the carb idle scews for max speed and ultra smooth at idle rather than as lean as it will run without missing. I know what the book says but they didn't know a few things about emissions and combustion efficiency back then and the instructions were for working tractors not parade tractors. The main jet if set rich for max power all the oxygen in the combustion chamber is used by having a slight surplus of fuel. Gasoline exhaust should be a clear vapour without dark puffs. Max fuel economy and clean combustion with clean combustion chambers,clean oil and clean exhaust uses all the fuel in the combustion chamber by having a slight amount of oxygen left over after combustion.All this by being a litle lean. The exact same as setting the fuel mixture on the shop oxy-acetolyne torch.

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