Old dogs do learn new things!!! LOL

JD Seller

Well-known Member
I have worked on many JD 3000 and 4000 series gas tractors. I posted back in April about the problems and things I have tried on them to "fix" them so they run correctly. Never really having much luck.

Against my own better judgment I bought a JD 4020 gas. It has a wide front end, JD canopy, and a real nice Allied quick tach loader. Truthfully I planned to just take the wide front, and loader off an put them on a diesel JD 4020 I have. The trouble is this tractor runs like a Swiss watch at idle or a little above. After that it is belch and stumble while having zero power to even pull itself let alone use it for anything requiring HP. So we have been using the gas tractor just around the shop with the loader. Wednesday I need a loader at another location. I drove it over. What a trip!!! LOL Had to drive at 1200 RPM in 6th gear to get there.

So Friday I decided to tear into the JD gas 4020 and find out what is wrong. Well the spark plugs where black as coal. They had less than 10 hours on them. So I installed new spark plugs and that helped a little bit but not much. So I took the carburetor off and brought it home. I went to take it apart to clean and found out it was an almost "new" Robert's rebuilt carburetor. Every thing was new, clean and seemed to be OK.

So I grabbed my JD 4000 series service manual and did some "light" reading last night. I read the entire section on the Zenith carburetor. I learned a few things.

1) The idle adjustment screw is actually adjusting air flow not fuel flow. So in actually increases the fuel drawn as it restricts the air flow which increased the velocity which makes it pull more gas through the idle circuit.

2) The accelerator pump pistons are adjustable. The lower one has three notches on the rod. The closest notch to the top is FULL flow and low fuel economy. Meaning the most fuel shot in during acceleration. The lowest slot is for lower fuel flow during acceleration and Highest fuel economy.

I did not know either of these things. I always assumed that in on the idle adjust screw meant less fuel. Plus I did not know that you has adjustments on the accelerator pistons.

So I reinstalled the carburetor with a new air filter just to be sure that there was not a restriction on the air intake side. I started with the idle set at 1 1/2 turns out and the load jet at 2 1/4 turns like the manual says to do. The tractor started right up. I let it warm up and then adjusted the idle leaner as I still has too rich of a fuel mixture at idle which was black smoking a little bit. I ended up at 4 full turns out on the idles screw. I then adjusted the load screw. I ended up at just a little over 1 3/4 turns. The tractor runs pretty good. It will take load and accelerate like it should. There is little dark exhaust too.

I went an bush hogged ten acres of pretty big horse weeds down. The tractor pulled great. It will be interesting to see if it will last. If it runs better I might leave the loader on the gas tractor as I will be mainly using it around the shop and house. It will not get high usage.
 
On my 1950 IHC tractor I found that part of the carb info was in the owner's manual, part in the I&T manual, part in the service manuals, .... I put it all together and found how to adjust my carb. Point being, you have to read all these different manuals to get a complete picture.
 
Glad you got her figure out JD, at least for now? Hopefully it will stay that way for you. I'm a diesel guy, so it just comes naturally to me to have never been impressed by any of the bigger gas tractors of any make.
 
Russ I knew the plugs were just a symptom not the root of the problem. It was frustrating knowing you have an over fuel issue but can't get it solved. I am not sure it is now. It will take time to see if it does.
 
You are the first person ever to get a 4020 gas to run decent. You could become a very rich man just traveling the country working your magic.
 
Flying Belgian: It is running well for nowwwww. LOL I would not bet that it will even start and run tomorrow let alone in a weeks time. I fought a JD gas tractor on my feeder wagon for years. Finally surrendered and replaced it with a diesel.
 
Mike JD switched the gas and diesels to paper filters in 1966 at 119,000 and up. This one is a 68 model. Nothing rare about it other than it had a real good loader on it.
 
Dont know much about the post,,,but have to ask if its ok,,,how many tractors do you and your sons have?,,,Just a friendly question,,Nosey,,,but friendly,,,,lol
 

I am really surprised, given all that you know, that you didn't know about the low speed screw. But I guess that since you know so much more than me about so many things, that I need to cut you some slack, LOL.
 
(quoted from post at 04:11:38 06/26/16) Dont know much about the post,,,but have to ask if its ok,,,how many tractors do you and your sons have?,,,Just a friendly question,,Nosey,,,but friendly,,,,lol

Larry, I guess we won't hear from JD for a few days now while he goes all around the different farms counting them.
 
Worked for years on dirt bikes, ATV's, lawn mowers and such. Nothing more frustrating than knowing something SHOULD run right, ISN'T running right, and you can't seem to figure out why.
 
Larry You can count them: LOL Remember this is myself and four sons plus my wife owning them. So it is not that many per person.
2- JD 8330s
JD 4960
JD 8410
2- JD 4455
2- JD 4450
3- JD 4440
JD 4040
4-JD 4020
JD 5210
Oliver 1655 (Uncle's Tractor)
IH 1466 (Grand Father's tractor)
Ford 981 (Non running)
39 JD "A" ( Wife's Father's tractor)
47 JD "G"
JD 40,50,60
JD 530
JD 620
Case VAC

I used to have more JD two cylinders but about ten years ago I got rid of all of them but ones that have sentimental value. I have not shown any tractors at a show in over 11 years. Several reasons: Kids grown and no time are the biggest ones. Also the JD Correction Police got so bad that at the last show I about decked a fool arguing with my wife about her Father's tractor. On the ride home we both agreed that that would NEVER happen again. So we sold the majority of the JD two cylinders and now only have a few non family people that see the tractors. My youngest son is showing some interest in some parades but that will be his deal. I am done, just do not have the time, interest or the energy anymore to fool with shows and parades.
 
Showcrop: Truthfully it was personal arrogance that is part of the reason on the low speed screw. I thought that these things are so simple why read the manual completely. I usually had just skimmed the book looking for the spec and such I needed not really reading ALL the details on carburetor section. The Power shift section I read completely every now and then when ever I fool with one.

Also I am willing to bet that this JD GAS tractor is not permanently "fixed". I just have little faith in JD waterloo gas tractors. The bigger the more issues they had/have. The Dubuque and Mannheim gas tractors seems to run better. Heck even the JD 2010 usually ran OK from a fuel stand point.
 
NY 986 Your correct. LOL It is over at my one son's and I have not seen it in a while. I forgot about it. It and the one JD 4020 where bought new by my Grand father. There also are several tractors that could be repaired or used as parts tractors. I did not list them.
 

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