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John Deere Tractors Discussion Forum
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JD A runs stronger on one cylinder

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b_board

04-05-2008 08:30:37




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I have a 51 A that I bought last year and have been working on ever since. At idle to mid range on the throttle you can pull # 2 wire off and hear no difference on how it runs. If you pull # 1 wire off, the motor slows down and sounds sluggish. I have rebuilt the mag, carb, new wires, new plugs, ajusted tappets, and compresion is about 120 psi on each cylinder. As far as plugs go I have tried ac delco C88L and champion D23. The tractor runs good under load no matter what rpm it is at.Is this common???

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bigblock

04-05-2008 18:07:26




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 Re: JD A runs stronger on one cylinder in reply to b_board, 04-05-2008 08:30:37  
My 730 is backasswards #2 is the main cylinder,but if I pull either plug wire off I can definetly tell a differance in the sound.#1 doesn't slow the engine down near as much as #2.



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buickanddeere

04-05-2008 09:47:42




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 Re: JD A runs stronger on one cylinder in reply to b_board, 04-05-2008 08:30:37  
Normal.

Throw the Champion plugs away and use Autolite 3116, AC Delco C88L or Denso 3020 and solid core wires.
Keep the coolant temp at 195 and lean out the idle until it almost stumbles on the good cylinder too.



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old

04-05-2008 09:39:03




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 Re: JD A runs stronger on one cylinder in reply to b_board, 04-05-2008 08:30:37  
Thats just the nature of the beast. When it is working hard it will fire like you think it should but when its idling and not working hard it will do that. Thats where the term popping johnny comes from



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John T

04-05-2008 09:13:34




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 Re: JD A runs stronger on one cylinder in reply to b_board, 04-05-2008 08:30:37  
All that (assuming all else like compression and ignition is equal) has to do with the fact its only a single barrell carb (and common port manifold) that feeds BOTH cylinders PLUS the 0 Degree (left) then 180 degrees later (right) cylinder firing. The residual vacuum and fuel in the manifold is present (theres a 540 degree coast cycle after 2 fires before 1 does remember)and the left No 1 cylinder gets as good charge of gas at idle as compared to the right cylinder.

Also ponder this; The Pop Pop Pop Pop you hear IS NOT the left then right cylinders firing, the noise (pops) you hear is the COMBINATION ADDITION of BOTH firings. If you heard each cylinder fire the noise would be POP POP - - - Pop Pop. Left fires,,,,, 180 later Right fires, 540 coast cycle, starts all over again. If you do the math and look at the human ear response curves, it all jumps out at ya. I think it was JR Hobbs or Duane Larson that also explained all this a few years back??

Make any sense at all lol ????? ????? ?

Thats my story n Ima stickin to it

John T

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Skyhawk Greg

04-08-2008 06:44:24




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 Re: JD A runs stronger on one cylinder in reply to John T, 04-05-2008 09:13:34  
Unless the human ear has changed since the late 70's, any sound that is received by the ear within 30 msec of the initial sound, tends to reinforce the initial sound. There is a grey area between 30 msec and 90 msec, and anything received 90 msec or more after the intitial sound, can usually be discerned as a second, distinct sound. Doing the math, the 30 msec time interval would correspond to the crank turning 180 degrees (distance between power strokes) at about 1000 rpm. The 90 msec time interval would correspond to about 1/3 of that, or 333 rpm. We know that several of the old two cylinder JD's run a bit more slowly than 333 rpm, but the reason for having difficulty hearing two distinct power strokes, at this point, has to do with the duration of the power stroke sound emission itself. In other words, the exhaust note from the first cylinder has to have decayed below the threshold of hearing more than 90 msec before the beginning of the second cylinder exhaust note in order for a person to hear two different exhaust notes. Greg

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b_board

04-05-2008 09:52:46




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 Re: JD A runs stronger on one cylinder in reply to John T, 04-05-2008 09:13:34  
This is an answer that I am glad to hear, to me it sounded like a valve sticking. The motor rpm does not change when I pull # 2 wire off, but I guess not knowing the fireing sequence was not helping me solve this problem. Thanks for your time.
B_BOARD



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THE SMOOTHED DEERES

04-05-2008 08:33:10




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 Re: JD A runs stronger on one cylinder in reply to b_board, 04-05-2008 08:30:37  
Read John T's post in the previous question posted . Number one always burns better .



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THE SMOOTHED DEERES

04-05-2008 08:41:11




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 Re: JD A runs stronger on one cylinder in reply to THE SMOOTHED DEERES, 04-05-2008 08:33:10  
There is a reason number 1 gets a better mixture at medium idle and down ,i beleive it's the carb ? Maybe John t will go into that (other story ) .



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