8N Sputtering after Heating Up

I have a 52 8n that is 6 volt with side mounted distributor. Runs great when started up, but after about 30 minutes of running it will start to run really rough. If I pull on the choke a little, it will smooth out somewhat. Once it cools back down for 30 minutes or so, it will fire right back up. I have seen elsewhere on the forum that this could be an issue with the coil? I recently replaced the plugs (Autolite A437), points, condensor, rotor, and cap.

These tractors are pretty simple machines; it’s usually pretty easy to get them running with some basic troubleshooting steps. You can:

1. Replace every part you can until it starts or you run out of money.

2. List every possible cause of the problem and then randomly pick your favorite to check. It could be your coil. Or your ignition switch. Or about 10 other things.


3. Like diagnosing any other equipment failure, take a step-by-step approach, working from the most likely to the least likely, one system at a time.



I’ve tried all three approaches. The third one always worked for me.



I might not be able to tell you why your tractor isn’t running, but I can tell you how to figure it out for yourself.


You could have a spark issue.


You could have a fuel issue.


Don’t guess. Troubleshoot. See tip # 13 at the link below.


You need to answer 2 questions before you do anything else:


With the bolt in the carb bowl removed and the gas on, will the fuel flow fill a pint jar in less than 2 minutes?


Next, get out your adjustable gap spark checker * , open the gap to 1/4", hook it up, turn the key on and crank the engine. Does the spark jump 1/4"? Post back with the answers.


And do not buy a new part for the tractor until you can answer this question: how do I know the part on the tractor is defective?

Once you narrow the problem to spark or fuel, post back and tell us what you found (and how you found it) and you will get plenty of help to get your tractor running.



* Don't own an adjustable gap spark checker? Buy one! Not a test light! Until then, take an old plug, open the gap 1/4" ground it to the head & look for spark. It’s not the color of the spark that counts; it’s the distance it jumps.

https://www.autozone.com/test-scan-and-specialty-tools/ignition-tester/oemtools-adjustable-ignition-spark-tester/10257_0_0?cmpid=PLA:US:EN:AD:NL:1000000:TLS:71700000043798748&gclid=Cj0KCQiAovfvBRCRARIsADEmbRKBdAvAmtFfOvYiYXR7T6NYiW57uyv5-dEKjVT_h2KogQNUUMsRixYaAlU3EALw_wcB&gclsrc=aw.ds
75 Tips

I've got good spark at 1/4" gap on spark plug tester.
Removing screw from the bottom of the carburetor and I've got a good flow of gas.

I have not checked spark after engine heats up (when the problem seems to start).

It means little to know wha the spark looks like when it is running good! Check it when it starts to act up. If spark is bad when hot, you might try jumping around ignition switch. notice I said jumping around it, not replacing, at least until you prove it is bad. good luck

Just wanted to close the loop on this thread. Checked the spark before the issue started and it was great at 1/4” gap. Checked again after problem started and it was still great. From there, I went back to the manual and adjusted the main idle screw and that solved the problem. Not sure why it started running rough, but glad the problem was easy to fix.