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Tractor Talk Discussion Forum

Misfiring @ idle John Deere A

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Roy Miller

01-27-2005 13:05:01




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Hope someone out there can help. My John Deere A misfires at idle. We have changed the carburator, magneto, plug wires & plugs, done valves and checked rings and still have same problem. Anyone have any suggestions as what to check next?




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mbptractor

01-27-2005 17:40:57




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 Re: Misfiring @ idle John Deere A in reply to Roy Miller, 01-27-2005 13:05:01  
Roy you can work on it and put a lot of money in to it but you will not fix this problem. it is the nature of these 2 cyl. i guess thats what make them so unique.



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DRL

01-27-2005 17:03:26




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 Re: Misfiring @ idle John Deere A in reply to Roy Miller, 01-27-2005 13:05:01  
Roy,

This is the nature of the beast. With the single barrel carb and the firing order, all of those letter series two cylinders will miss, especially on the right hand cylinder. The John Deere two cylinder engine has a unique firing sequence. The #1 (left) cylinder fires, then at 180 degrees afterward, the #2 (right) cylinder fires. Then there is one and one half (540 degrees) revolutions of the crankshaft when neither fires. Then the sequence starts again. The left hand cylinder gets a fuller, richer charge of fuel vapor from the long 540 degree cycle whereas the right hand only has the 180 degree cycle to get it's charge. It will miss and pop at idle, (hence the nickname "Johnny Popper"), but put under load, both cylinders fire equally since the governor has opened the carb plus more vacuum pulling the fuel mixture through the carb and manifold. If you pull the plug wire off of the lefthand cylinder, the right hand cylinder will then start firing. Try it. If this doesn't help, post back and we'll go from there.

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Rockin' Farmer

01-27-2005 19:26:46




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 Re: Misfiring @ idle John Deere A in reply to DRL, 01-27-2005 17:03:26  
DRL

You are exactly right. Sort of gives them their charm.

Rockin' Farmer



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mattd

01-27-2005 14:05:43




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 Re: Misfiring @ idle John Deere A in reply to Roy Miller, 01-27-2005 13:05:01  
because of the timing and exhaust routing, it may sound like it is missing. i believe it fires at 540 and 180 degrees. and since cylinder 1 exhaust has a farther path to take, it may sound like its misfiring. but if you really think it is misfiring, take one spark plug wire off and see if it gets worse. if it does then that one is fine. then take the other off and if it doesnt make a difference then thats the dead cylinder.

matt

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RAB

01-27-2005 13:24:05




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 Re: Misfiring @ idle John Deere A in reply to Roy Miller, 01-27-2005 13:05:01  
Have a look to see if there is one or more cylinders missing.
RAB



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