JD 420 Missing Badly and Running Rough

I have an old JD 420 2 cylinder that has started missing badly and running rough. Last spring I had similar issues and I thought it was electronic related. I replaced the spark plugs, wires, condenser and points, nothing helped. I ended up taking out the fitting in the bottom of the gas tank and it was plugged with junk. Once that was cleaned out, it ran great the rest of the summer. So far this year it was running great until this week when I hooked up the disk to run over the garden. It ran good for a couple of turns and then it started missing and would barely pull its self. Last night I drained the gas tank and removed the fitting in the bottom of the tank again. I also removed the carburetor. I took everything apart and cleaned with gas and carb cleaner. I put it back together and filled the tank with new gas. It started right up, but I have the same issue. I?m not much of a mechanic, so any advice would be helpful. Thanks

I would look at the mag-distributer cap . Sounds like cracked cap .

You might consider changing out the condenser.

A bad/faulty condenser can make the tractor act as if it is running out of gas.

You might also remove the oil cup from the bottom of the air cleaner.

Start the tractor and notice any changes.

If the tractor appears to run better, then clean out the oil cup and add fresh oil.

Also make sure to clean out the air cleaner.

Hope this helps.

Did you take the elbow off the carb and clean the screen?

My MT did this to me and it was a bad condenser. I have had bad condensers out of the package before too. I used to keep two on hand.

Those are noted for worn distributer shaft bushings

Thanks everyone for the replies.

hotflashjr, I changed the condenser last year when I was having issues. I'll add that to my list of things to try. M-man, I'm not sure what the elbow is. I did take off the sediment bowl and sprayed carb cleaner thru the screen that set above the bowl. JamesH, I cleaned the oil cup and changed the oil a couple of weeks ago when I serviced everything for the spring. Donmyeil, the distributor cap is the one thing I didn't change last year. I'll add that to the list of things to try as well. Thanks again.

Does it runs better with the choke partially closed? If yes, it's running lean.

The elbow is a square looking brass fitting that the gas line attaches to on the carb. Remove the gas line from the carb and you can unscrew the elbow. Lots of times the screen in there is rotten.

hotflash, after reading your earlier post, I went to the parts catalog and found it. I'll take that off and clean it out. Thanks.

Champion Spark Plugs? If so throw them out and get a pair of real ones (AC, for example)

Same problem on my M, turned out to be a bad condenser. The condenser went bad after only a few hours of operation after installing a new one.

I agree with trying another condenser. I had a bad one last year right out of the box from John Deere. Junk from China

In the old days we replaced the condensers whenever we changed the points. They were probably still good. The ones today are garbage and if you get a good one, hang on to it. I have had a high number of new ones be bad out of the box or fail very soon. They are all imported and they are not a high usage item any more in ignition systems and only used on old tractors and antique cars, etc.
CPeter

lots of replies here but did not notice that Alcyone suggested taking the drain out of the bottom of the carb and checking for as steady flow of gas. let it flow for a while to see the volume that is coming through the system not just what was in the carb.

Also had an ignition switch go south on my 420. That can be checked by taking the wire supplying power to the coil off and substituting a jumper from the lug on the starter to the coil.

Thanks everyone for taking the time to offer your thoughts and suggestions. I took the carb off tonight and brought it to the shop. I did take out the elbow and checked the screen. It looked clean, but I'll do a better job of cleaning it tomorrow. I have a carb rebuild kit that I got last year to replace a broken throttle shaft. I only used the shaft, but will use the rest of the kit and rebuild the carb tomorrow. I'll pick up another condenser and try that as well. I did run the tractor a while tonight and I tried pulling out the coke but that had no effect. I'll keep tying the suggestions. Thanks again for all the help.

Check the fly-weights in the distributor and make sure they are free to fly and not gummed up. If you remove the dist mark it before and retime with a light after reinstall.

I received so much great advice here and also last spring (same tractor similar issue), I thought I'd give you an update. I cleaned the carb again this week and put it on this morning. I also took out the plugs and cleaned them, I didn't have new ones and I had put these in last spring. I checked the points and re-set them and checked the dist.cap for cracks. I checked to see if the distributor bushing seemed ok and they did to me. I didn't have another condenser, but I had changed it last spring. I started it up and took off. It ran pretty good, though not as well as you might like. After about 5 minutes it began missing so bad I didn't think I'd get back to the barn. When I got back to the barn, the only thing left to try was to replace the condenser that I put in last spring with the old one, which I still had. I put the old condenser back in and it ran like a new John Deere 420. I ran around the farm for 15 minutes and hooked to the disk and disk the garden. Ran perfect the whole time. I know a bunch of you said to check the condenser, so thank you!! Thanks for all of the other good advice that I received as well. First chance I get, I'm gonna pick up two new condensers to keep in the tool box. Thanks again everyone.