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John Deere Tractors Discussion Forum
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620 running rough

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John VB

11-03-2006 20:29:18




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My 620 usually runs great, however, recently it hasn't been running well. It will start and seems to run rough with no power. If you try to drive this way it starts to die. After a couple of minutes (the time varies) you can hear it suddenly run normally. I pulled a spark plug and it is heavily coated with soft, black carbon. I think I may need a hotter plug. I believe I have Autolite 386s in there now. What would be the proper temp plug? It doesn't get run a lot and never hard. Plug wires, distributor, points, etc are all ok. Thanks.

John VB


Thanks.

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Glen in TX

11-04-2006 09:37:50




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 Re: 620 running rough in reply to John VB, 11-03-2006 20:29:18  
If 620 gas pull the intake off carb and see if it runs any better after you get ignition, plugs and wires right. If so suspect a plugged air cleaner or mud daubers nest or if you had it outside and water got in air cleaner and then made a sludge pie come loose inside it's probably plugged up too much. See too many air cleaners that never been cleaned or had any attention in 40-60 years and eventually they get plugged worse when moisture or bugs enter them. Sometimes we get outbreaks of those beetles here in June or July and those things crawl into everything including a air stack or intake of a engine sitting not running. Check the fuel flow to carburetor too and see if you got stuff floating in tank or if gas is maybe just too old and rancid.

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John VB

11-05-2006 05:37:59




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 Re: 620 running rough in reply to Glen in TX, 11-04-2006 09:37:50  
Thanks for the reply Glen. I put in the new points and plugs and the ignition side of things SHOULD be ok. Gas is fresh and never gets too old. It didn't start very well, but seemed to be running ok. I was driving it around and all of a sudden it started to stall. Running rough and no power. I limped back to the shed in first gear. Had to keep the choke out a little to keep it running. Seemed to be running on one cylinder. I need to pull a plug wire when running like that to confirm I guess. Have the plug covers so I will take them off for a while.

I tried to back it into the shed, but didn't have enough power to use reverse. All of a sudden, it started running well again.

Once in the shed, noticed there was gas dripping off the bottom of the carb bowl and dripping down both idle adjust screws. Don't know if that is a sign of what is causing my problems. Both spark plugs had gas on the threads. Should probably pull the carb. I,m sure it could use a new valve and seat anyway. Perhaps the float is fuel-logged. I will first check to see if the air supply is restricted. I need to get it going again before show-pushing season is here.

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Glen in TX

11-04-2006 10:14:21




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 Re: 620 running rough in reply to John VB, 11-05-2006 05:37:59  
Sounds like you found it there describing the carb with fuel running down and probably needs a needle seat kit or some trash stuck in it. Fresh plugs and carb kit sounds like.



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John VB

11-07-2006 17:39:05




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 Re: 620 running rough in reply to Glen in TX, 11-04-2006 10:14:21  
Any comparisons between the JD carb kits and the kits available from other places? I have a JD dealer two miles away and they are pretty good about getting stuff for me. I will have to get the two gaskets on both sides of the carb from them anyway so will probably just get it all there.



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Glen in TX

11-07-2006 22:30:33




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 Re: 620 running rough in reply to John VB, 11-07-2006 17:39:05  
JD is fine if you like the price. The OEM kits from Zenith won't have everything for a complete rebuild. Roberts Carb has some good gaskets and kits too.



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John VB

11-09-2006 05:44:30




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 Re: 620 running rough in reply to Glen in TX, 11-07-2006 22:30:33  
Glen,

Thanks for the carb repair kit link. I called JD and they want $160. I'm sure it is a very complete kit. Lots of $ though. I found the one below. Not sure how it compares to the Roberts kit as you can't see everything on their website. For only $20, it probably doesn't contain the same stuff.

Link

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Glen in TX

11-09-2006 10:25:02




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 Re: 620 running rough in reply to John VB, 11-09-2006 05:44:30  
Never bought their kits but have used some from Roberts that are good quality. I just use the OEM Zenith kits but those won't work for everyone as you got to have more NOS parts to go with them. Many places sell aftermarket ones that just don't have good gaskets in them. A complete kit should really include a new throttle butterfly plate as well as shaft and bushings because if shaft and bushings were worn bad the butterfly is worn some too at edges and will just hang up or not idle well so check those out close. You may also want to clean out passage ways and get some numbered drills to clean those and Roberts sells them. You see other drill kits online but many don't have all the right sizes you need.

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John T

11-04-2006 05:08:01




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 Re: 620 running rough in reply to John VB, 11-03-2006 20:29:18  
John, The Autolite 388 is a lil hotter but you may wanna try the 3116 which is a NON resistor plug instead. Make sure the wires are wire core NOT carbon core suppressor types and that the points are gapped correct and NOT gray oxide coated, but if so, non abrasively clean/buff/polish them with a dollar bill or shop cloth drug between them. It can also help if you can get the operating temp up to 180 and over and dont run the carb over rich and also make sure the air inlet piping and air cleaner bowl are clean n not clogged up and that the choke buterfly plate is fully opening n staying open. I never had near so much a problem of plugs fouling on those 2 barrel carbs and the distributor ignitions as on the old one barrel mag equiped tarctors.

John T

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John VB

11-04-2006 05:18:08




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 Re: 620 running rough in reply to John T, 11-04-2006 05:08:01  
Thanks John T. The points are new and gapped correctly. The plug wires are fairly new and wire core. The air cleaner should be ok, but I will check anyway. I think the choke is ok. Only other variable is whether it is running too rich. I am not getting black smoke except when quickly throttling up. How can you tell if you are running rich? It really runs well most of the time.

John VB



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John T

11-04-2006 06:43:09




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 Re: 620 running rough in reply to John VB, 11-04-2006 05:18:08  
Im NOT any expert on the 2 barrel carbs but basically if it only throws black smoke on throttle up and it does NOT show excess black smoke otherwise, I'd say its fine. My 620 used to blacken one plug time to time also and it wasnt over rich and the choke stayed full open as it should and I figured it was a tad low compression on that side but if you use it hard and get the temp up over 180 n keep it there the problem goes away, but thats hard if you only use it for light loads short times grrrrr rrr

Try 3116 plugs n check the air cleaner bowl n see what happens???

John T

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machinery-man

11-04-2006 02:53:46




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 Re: 620 running rough in reply to John VB, 11-03-2006 20:29:18  
go to electronic ignition and you"ll solve a lot of problems.



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John VB

11-09-2006 07:29:58




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 Re: 620 running rough in reply to machinery-man, 11-04-2006 02:53:46  
Machinery-man,

Which electronic ignition conversion kit do you recommend?



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