Need advice on JD 520 tractor

David from Kansas

Well-known Member
Acquired this tractor a few months ago. Hard starting, even with good battery. Finally no start, period. Put all new electrical components on it; dist cap, points, condenser, rotor, all new solid core wires, new spark plugs. Changed out the gas in the tank. Still no start. Not even an occasional fire. Pulled it, started on one cylinder but wouldn't stay running. Had carb professionally rebuilt. Still no start, wouldn't even fire. While checking for spark at plugs, noticed (got me! that's why I noticed) spark jumping from spark plug wire to spark plug cover, which was grounded on the tractor. So....problem found. Taped up the wire and boot, but still no start. While cranking, was trying at various throttle settings and while the throttle lever was completely to the rear, at extreme slow idle, it started firing so gave it a tiny bit of throttle and it took off. Been able to get it started after that with the throttle completely in the slow idle position. Will not start if the throttle is advanced even a tiny bit. Runs great and seems to have good power. What the heck!!!!
 
My '60' is much the same engine. They all start a little differently (don't know why - atmospheric conditions - time ? ) My drill is (and always has been, even before new rings and relined cyl.,head rebuild, new ignition etc). IS; 1/4 throttle, full choke and about 2 rhumpas- going. This thing took the same process when it was only running on 1 Cyl. ! HTH
 
I haven't rebuilt any of the 20 series tractors, but my model a and my g will do the same thing if I don't shut the fuel off the g espically. Had both carbs rebuilt but it seems that if they sit for a little bit and I maybe wrong but fuel will find its way into the engine with a perfectly set up carb with no issues and flood it out which can cause sputtering starts or no starts unless you crank and crank and crank, until either the fuel gets burned out of the cylinders or is pushed into the crank case which is bad. essentially all you are doing is choking the engine with the throttle all the way back and not letting any air and fuel into the cylinders. If your tractor has petcocks try opening those after the tractor has been sitting and see if it blows fuel out if it does then you may have found your problem. I am by no means an expert but know enough to get me into trouble...
 
When it is cool out, I haver to choke it for a couple of revolutions and then it will start to fire. Sometimes have to let the choke about half out after it starts, for a minute or two until it warms up just a tad. No petcocks so can't do that test, however I'm competent it doesn't flood while sitting as there is no excessive smoke, etc., when it starts. The automatic fuel shut-off seems to be working as fuel can be seen flowing into the sediment bowl while cranking.
 
Mine always started reliably with throttle 1/2 and full choke until it fired, then choke all the way in. I damaged the carb and had it rebuilt by a JD-knowledgeable man who used Roberts kits, tools and methods. Put it back on and started miserably, sometimes using all of the (very cheap) battery. Throttle tried all over, choke same, no joy. Then one day I accidentally left the throttle fully closed and it boomed right off. Huh?? It ran so slow it barely raised the oil pressure, but after 2-3 minutes it would take gentle throttle and from there ran normally (a chancy term for 2 cyl JD). I had exactly your condition. I've learned to live with it and can start it with it open a little bit when the weather's 90* or above. When it's cold weather I still need full choke until the first sign of wanting to start then full in. Hope yours stays reliable, if goofy, too!
 
Well those old two lungers can be quirky, and since they were built by hand no two start or run the same, and depending on what things have been done to the engine and what part of the country you are in can make a difference too, as long as you have all of the things that make it go pop pop and it isn't running like garbage I would just say its the way your particular tractor starts and runs. My model a took forever to start here in Arizona but once I got it too Wisconsin it only takes 2 to 3 pulls to get it started (saved my arms once it got back there)and to me it ran smoother on a engine that was put back to stock with NOS cast iron all fuel pistons.
 
On John Deeres, most people claim when cold, slight throttle, full choke. They will turn over once or twice and then fire. As soon as it fires open choke. You might have to feather the choke when it starts. That is exactly how my 52 A is. Strangely enough, my 520 starts great without choking. Have you tried without choke?
 
I think your looking at the wrong issues. I think you have a vacuum leak in the intake manifold. Could be cracked or bad gaskets but I would lean towards cracked.
 
Thought of that early on but didn't see any evidence of cracks. Gasket leakage could be another issue. How is best to check for leak? Didn't mention it in earlier posts, but this tractor idles extremely well. Better than any I have ever owned. It will accelerate from a slow idle without stumbling. Also considered carb adjustment. I did open the two idle screws 1/2 turn but it didn't make any noticeable difference. Maybe I should keep opening them a little at a time to see if it affects starting.
 
(quoted from post at 17:57:15 08/23/18) On John Deeres, most people claim when cold, slight throttle, full choke. They will turn over once or twice and then fire. As soon as it fires open choke. You might have to feather the choke when it starts. That is exactly how my 52 A is. Strangely enough, my 520 starts great without choking. Have you tried without choke?
xactly how my 520 starts too with no choke. No throttle either always fires right off.
 
The reason they start better with the throttle closed is because the air is drawn through a smaller opening in the carburetor throat. This causes the air to travel at a higher velocity which in turn better atomizes the fuel so it is more volatile and ignites easier. Today's automotive gasoline is made to be atomized with a fuel injector instead of a carburetor so it is less volatile than gas from 50 years ago.
 
Usually with a leaking gasket you need it running at idle. Then spray brake cleaning fluid around the manifold. IF the engine speeds up you now you have a leak.

IRC those manifolds can crack internally. I can remember right of the top of my head it this one has the exhaust as an integral part or if the JD 520 has the two separate ones that are stacked. If it is the two piece one that is stacked, then it can't crack internally and cross over into the exhaust side.

Too early in the morning for all the brain cells to be working. LOL
 

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