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John Deere Tractors Discussion Forum
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620 duplex carb idle needle adjust

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John VB

12-04-2006 20:21:36




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I got my carb back from Roberts. I stripped it and sent it to them for cleaning. Put it all back together and installed it. Seems to run really well. I adjusted all of the linkages per the carb manual. I then tried to adjust the idle needles. I initially had them out 1-1/2 turns. I shorted out the #1 (left) plug wire and was adjusting the #2 (right) idle needle. It made no difference in engine rpm whether I turned it in or out. Always ran at about 360 rpm. Just kept right on putting along. Finally gave up and hooked the plug back up. I then adjusted #2 until the tractor sounded the best. Also picked up a few rpms. Am I missing something? Is this a critical adjustment? I assume it is done so the cylinders are not fighting each other at idle. Thanks.

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Mike M

12-05-2006 04:30:50




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 Re: 620 duplex carb idle needle adjust in reply to John VB, 12-04-2006 20:21:36  
I think the basic idea is to get them running the same rpm so they don't fight each other. One side will usually only go so fast, so you turn the needle in to slow down the faster cyl. to the speed of the slower one. Make sure it is warmed up and I slip a piece of weldeing wire under the wire terminals and use a jumper wire lead with clips on the end to short out one side then the other. This way loose spark isn't flying around which can also hurt the coil and other parts.

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machinery-man

12-05-2006 04:04:43




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 Re: 620 duplex carb idle needle adjust in reply to John VB, 12-04-2006 20:21:36  
I"ve never thought much of the recommended adjustment method...generally just backed off about 1 1/2 turns and if tractor ran okay left alone. I would say if you get them a too lean you will have cold starting and acceleration problems.



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