Dear Ole Mechanic;

I have a 1958 John Deere 730 tractor that I use in my orchard. Recently, I was disking around the peach trees to keep the weeds down, and the 730 worked hard all day without any problems.  However, as we neared the end of the day, the 730 started to lose power.  I closed the choke a little, as it seemed to be running lean, and it picked back up for a little while, but then it got worse and finally died.  I cleaned the sediment bowl, even though it really wasn’t all that dirty.  I can get it to fire once or twice when I try to restart it, but it won't keep running.  After I cleaned the sediment bowl, it refilled quickly, so the gas seems to be getting that far OK, I suspect  that somehow some junk got past the sediment bowl screen and is plugging up one of the small passageways in the carburetor. John Deere730 1

What do you think?

Deere Driver

Dear Deere Driver;

I agree with your thinking on this; although, there are a couple of other things that could cause the same problem.  Like you, the first thing I would check is the fuel delivery to the carburetor, and then I would take the carburetor apart and check for plugged passageways.  If you don’t find anything, then one of the other things to check will be the ignition coil.  Usually a coil going bad will start by giving a weak spark.  Closing the choke will make the air/gas mixture richer and easier for the weak spark to ignite.  Finally, the spark will get so weak that it won’t ignite anything.  With the ignition switch off, the coil will cool off some and may fire once or twice when a restart is tried.  It will quickly fail again as the coil heats up from the electricity going through it.

Another ignition part that can fail in a somewhat similar manner is the condenser for the ignition points.  If it starts to fail by shorting out electrically inside, then you will get the same weak spark at first and finally no spark.  Usually letting it cool down does not help, so you won't get it to fire during a restart. 

John Deere730 2If, after sitting for awhile, the tractor fires up and runs fine, I would suspect the coil.  If it fires up but doesn't run very long, I would check the carburetor first, but would keep the possibility of a failed coil or condenser in mind.

About the only other thing that could keep the 730 from running would be low compression, but if the tractor has been running well up to this point, that probably isn't the problem.

Good luck! I hope you get your tractor up and running soon!

Herr Professor Nuzanbolts